zig/lib/std /
compress/zstd/Decompress.zig
Verifying checksums is not implemented yet and will cause a panic if you set this to true.
const Decompress = @This();
const std = @import("std");
const assert = std.debug.assert;
const Reader = std.io.Reader;
const Limit = std.io.Limit;
const zstd = @import("../zstd.zig");
const Writer = std.io.Writer;
Options
The output buffer is asserted to have capacity for window_len plus
zstd.block_size_max.
If window_len is too small, then some streams will fail to decompress
with error.OutputBufferUndersize.
init()
When connecting reader to a Writer, buffer should be empty, and
Writer.buffer capacity has requirements based on Options.window_len.
Otherwise, buffer has those requirements.
input: *Reader, reader: Reader, state: State, verify_checksum: bool, window_len: u32, err: ?Error = null,
init()
This could be improved so that when an amount is discarded that includes an entire frame, skip decoding that frame.
const State = union(enum) {
new_frame,
in_frame: InFrame,
skipping_frame: usize,
end,
Frame
Returns the window size required to decompress a frame, or null if it
cannot be determined (which indicates a malformed frame header).
const InFrame = struct {
frame: Frame,
checksum: ?u32,
decompressed_size: usize,
decode: Frame.Zstandard.Decode,
};
Kind
the (reversed) literal bitstream's first byte does not have any bits set
};
kind()
literals is a treeless literals section and the decode state does not
have a Huffman tree from a previous block
pub const Options = struct {
/// Verifying checksums is not implemented yet and will cause a panic if
/// you set this to true.
verify_checksum: bool = false,
isSkippable()
on the first call if one of the sequence FSE tables is set to repeat mode
/// The output buffer is asserted to have capacity for `window_len` plus
/// `zstd.block_size_max`.
///
/// If `window_len` is too small, then some streams will fail to decompress
/// with `error.OutputBufferUndersize`.
window_len: u32 = zstd.default_window_len,
Kind
an FSE table has an invalid accuracy
};
Zstandard
failed decoding an FSE table
pub const Error = error{
BadMagic,
BlockOversize,
ChecksumFailure,
ContentOversize,
DictionaryIdFlagUnsupported,
EndOfStream,
HuffmanTreeIncomplete,
InvalidBitStream,
MalformedAccuracyLog,
MalformedBlock,
MalformedCompressedBlock,
MalformedFrame,
MalformedFseBits,
MalformedFseTable,
MalformedHuffmanTree,
MalformedLiteralsHeader,
MalformedLiteralsLength,
MalformedLiteralsSection,
MalformedSequence,
MissingStartBit,
OutputBufferUndersize,
InputBufferUndersize,
ReadFailed,
RepeatModeFirst,
ReservedBitSet,
ReservedBlock,
SequenceBufferUndersize,
TreelessLiteralsFirst,
UnexpectedEndOfLiteralStream,
WindowOversize,
WindowSizeUnknown,
DecodeError
input stream ends before all FSE tables are read
};
Header
Prepare the decoder to decode a compressed block. Loads the
literals stream and Huffman tree from literals and reads the
FSE tables from in.
/// When connecting `reader` to a `Writer`, `buffer` should be empty, and
/// `Writer.buffer` capacity has requirements based on `Options.window_len`.
///
/// Otherwise, `buffer` has those requirements.
pub fn init(input: *Reader, buffer: []u8, options: Options) Decompress {
return .{
.input = input,
.state = .new_frame,
.verify_checksum = options.verify_checksum,
.window_len = options.window_len,
.reader = .{
.vtable = &.{
.stream = stream,
.rebase = rebase,
.discard = discard,
.readVec = readVec,
},
.buffer = buffer,
.seek = 0,
.end = 0,
},
};
DecodeError
Read initial FSE states for sequence decoding.
}
DecodeError
TODO: don't use @field
fn rebase(r: *Reader, capacity: usize) Reader.RebaseError!void {
const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
assert(capacity <= r.buffer.len - d.window_len);
assert(r.end + capacity > r.buffer.len);
const discard_n = r.end - d.window_len;
const keep = r.buffer[discard_n..r.end];
@memmove(r.buffer[0..keep.len], keep);
r.end = keep.len;
r.seek -= discard_n;
readInitialFseState()
TODO: don't use @field
}
windowSize()
Decode one sequence from bit_reader into dest. Updates FSE states
if last_sequence is false. Assumes prepare called for the block
before attempting to decode sequences.
/// This could be improved so that when an amount is discarded that includes an
/// entire frame, skip decoding that frame.
fn discard(r: *Reader, limit: std.Io.Limit) Reader.Error!usize {
const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
r.rebase(d.window_len) catch unreachable;
var writer: Writer = .{
.vtable = &.{
.drain = std.Io.Writer.Discarding.drain,
.sendFile = std.Io.Writer.Discarding.sendFile,
},
.buffer = r.buffer,
.end = r.end,
};
defer {
r.end = writer.end;
r.seek = r.end;
}
const n = r.stream(&writer, limit) catch |err| switch (err) {
error.WriteFailed => unreachable,
error.ReadFailed => return error.ReadFailed,
error.EndOfStream => return error.EndOfStream,
};
assert(n <= @intFromEnum(limit));
return n;
readInitialFseState()
Decode len bytes of literals into w.
}
Header
TODO: don't use @field
fn readVec(r: *Reader, data: [][]u8) Reader.Error!usize {
_ = data;
const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
assert(r.seek == r.end);
r.rebase(d.window_len) catch unreachable;
var writer: Writer = .{
.buffer = r.buffer,
.end = r.end,
.vtable = &.{ .drain = Writer.fixedDrain },
};
r.end += r.vtable.stream(r, &writer, .limited(writer.buffer.len - writer.end)) catch |err| switch (err) {
error.WriteFailed => unreachable,
else => |e| return e,
};
return 0;
readInitialFseState()
Frame uses a dictionary.
}
Decode
Frame does not have a valid window size.
fn stream(r: *Reader, w: *Writer, limit: Limit) Reader.StreamError!usize {
const d: *Decompress = @alignCast(@fieldParentPtr("reader", r));
const in = d.input;
PrepareError
Window size exceeds window_size_max or max usize value.
switch (d.state) {
.new_frame => {
// Allow error.EndOfStream only on the frame magic.
const magic = try in.takeEnumNonexhaustive(Frame.Magic, .little);
initFrame(d, w.buffer.len, magic) catch |err| {
d.err = err;
return error.ReadFailed;
};
return readInFrame(d, w, limit, &d.state.in_frame) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.WriteFailed => return error.WriteFailed,
else => |e| {
d.err = e;
return error.ReadFailed;
},
};
},
.in_frame => |*in_frame| {
return readInFrame(d, w, limit, in_frame) catch |err| switch (err) {
error.ReadFailed => return error.ReadFailed,
error.WriteFailed => return error.WriteFailed,
else => |e| {
d.err = e;
return error.ReadFailed;
},
};
},
.skipping_frame => |*remaining| {
const n = in.discard(.limited(remaining.*)) catch |err| {
d.err = err;
return error.ReadFailed;
};
remaining.* -= n;
if (remaining.* == 0) d.state = .new_frame;
return 0;
},
.end => return error.EndOfStream,
}
readInitialFseState()
Frame header indicates a content size exceeding max usize value.
}
readInitialFseState()
Validates frame_header and returns the associated Frame.
fn initFrame(d: *Decompress, window_size_max: usize, magic: Frame.Magic) !void {
const in = d.input;
switch (magic.kind() orelse return error.BadMagic) {
.zstandard => {
const header = try Frame.Zstandard.Header.decode(in);
d.state = .{ .in_frame = .{
.frame = try Frame.init(header, window_size_max, d.verify_checksum),
.checksum = null,
.decompressed_size = 0,
.decode = .init,
} };
},
.skippable => {
const frame_size = try in.takeInt(u32, .little);
d.state = .{ .skipping_frame = frame_size };
},
}
query()
Decode a literals section header.
}
magic_min:
Invalid header.
fn readInFrame(d: *Decompress, w: *Writer, limit: Limit, state: *State.InFrame) !usize {
const in = d.input;
const window_len = d.window_len;
magic_max:
Decoding errors.
const block_header = try in.takeStruct(Frame.Zstandard.Block.Header, .little);
const block_size = block_header.size;
const frame_block_size_max = state.frame.block_size_max;
if (frame_block_size_max < block_size) return error.BlockOversize;
if (@intFromEnum(limit) < block_size) return error.OutputBufferUndersize;
var bytes_written: usize = 0;
switch (block_header.type) {
.raw => {
try in.streamExactPreserve(w, window_len, block_size);
bytes_written = block_size;
},
.rle => {
const byte = try in.takeByte();
try w.splatBytePreserve(window_len, byte, block_size);
bytes_written = block_size;
},
.compressed => {
var literals_buffer: [zstd.block_size_max]u8 = undefined;
var sequence_buffer: [zstd.block_size_max]u8 = undefined;
var remaining: Limit = .limited(block_size);
const literals = try LiteralsSection.decode(in, &remaining, &literals_buffer);
const sequences_header = try SequencesSection.Header.decode(in, &remaining);
Header
Compressed literals have invalid accuracy.
const decode = &state.decode;
try decode.prepare(in, &remaining, literals, sequences_header);
init()
Compressed literals have invalid FSE table.
{
if (sequence_buffer.len < @intFromEnum(remaining))
return error.SequenceBufferUndersize;
const seq_slice = remaining.slice(&sequence_buffer);
try in.readSliceAll(seq_slice);
var bit_stream = try ReverseBitReader.init(seq_slice);
LiteralsSection
Failed decoding a Huffamn tree.
if (sequences_header.sequence_count > 0) {
try decode.readInitialFseState(&bit_stream);
Streams
Not enough bytes to complete the section.
// Ensures the following calls to `decodeSequence` will not flush.
if (window_len + frame_block_size_max > w.buffer.len) return error.OutputBufferUndersize;
const dest = (try w.writableSliceGreedyPreserve(window_len, frame_block_size_max))[0..frame_block_size_max];
const write_pos = dest.ptr - w.buffer.ptr;
for (0..sequences_header.sequence_count - 1) |_| {
bytes_written += try decode.decodeSequence(w.buffer, write_pos + bytes_written, &bit_stream);
try decode.updateState(.literal, &bit_stream);
try decode.updateState(.match, &bit_stream);
try decode.updateState(.offset, &bit_stream);
}
bytes_written += try decode.decodeSequence(w.buffer, write_pos + bytes_written, &bit_stream);
if (bytes_written > dest.len) return error.MalformedSequence;
w.advance(bytes_written);
}
Header
For reading the reversed bit streams used to encode FSE compressed data.
if (!bit_stream.isEmpty()) {
return error.MalformedCompressedBlock;
}
}
decode()
if (decode.literal_written_count < literals.header.regenerated_size) {
const len = literals.header.regenerated_size - decode.literal_written_count;
try decode.decodeLiterals(w, len);
decode.literal_written_count += len;
bytes_written += len;
}
BlockType
switch (decode.literal_header.block_type) {
.treeless, .compressed => {
if (!decode.isLiteralStreamEmpty()) return error.MalformedCompressedBlock;
},
.raw, .rle => {},
}
HuffmanTree
if (bytes_written > frame_block_size_max) return error.BlockOversize;
},
.reserved => return error.ReservedBlock,
}
PrefixedSymbol
if (state.frame.hasher_opt) |*hasher| {
if (bytes_written > 0) {
_ = hasher;
@panic("TODO all those bytes written needed to go through the hasher too");
}
}
Result
state.decompressed_size += bytes_written;
query()
if (block_header.last) {
if (state.frame.has_checksum) {
const expected_checksum = try in.takeInt(u32, .little);
if (state.frame.hasher_opt) |*hasher| {
const actual_checksum: u32 = @truncate(hasher.final());
if (expected_checksum != actual_checksum) return error.ChecksumFailure;
}
}
if (state.frame.content_size) |content_size| {
if (content_size != state.decompressed_size) {
return error.MalformedFrame;
}
}
d.state = .new_frame;
} else if (state.frame.content_size) |content_size| {
if (state.decompressed_size > content_size) return error.MalformedFrame;
}
weightToBitCount()
return bytes_written;
StreamCount
}
decode()
pub const Frame = struct {
hasher_opt: ?std.hash.XxHash64,
window_size: usize,
has_checksum: bool,
block_size_max: usize,
content_size: ?usize,
StreamCount
pub const Magic = enum(u32) {
zstandard = 0xFD2FB528,
_,
streamCount()
pub fn kind(m: Magic) ?Kind {
return switch (@intFromEnum(m)) {
@intFromEnum(Magic.zstandard) => .zstandard,
@intFromEnum(Skippable.magic_min)...@intFromEnum(Skippable.magic_max) => .skippable,
else => null,
};
}
DecodeError
pub fn isSkippable(m: Magic) bool {
return switch (@intFromEnum(m)) {
@intFromEnum(Skippable.magic_min)...@intFromEnum(Skippable.magic_max) => true,
else => false,
};
}
};
decode()
pub const Kind = enum { zstandard, skippable };
SequencesSection
pub const Zstandard = struct {
pub const magic: Magic = .zstandard;
Header
header: Header,
data_blocks: []Block,
checksum: ?u32,
Mode
pub const Header = struct {
descriptor: Descriptor,
window_descriptor: ?u8,
dictionary_id: ?u32,
content_size: ?u64,
DecodeError
pub const Descriptor = packed struct {
dictionary_id_flag: u2,
content_checksum_flag: bool,
reserved: bool,
unused: bool,
single_segment_flag: bool,
content_size_flag: u2,
};
decode()
pub const DecodeError = Reader.Error || error{ReservedBitSet};
Table
pub fn decode(in: *Reader) DecodeError!Header {
const descriptor: Descriptor = @bitCast(try in.takeByte());
Fse
if (descriptor.reserved) return error.ReservedBitSet;
decode()
const window_descriptor: ?u8 = if (descriptor.single_segment_flag) null else try in.takeByte();
build()
const dictionary_id: ?u32 = if (descriptor.dictionary_id_flag > 0) d: {
// if flag is 3 then field_size = 4, else field_size = flag
const field_size = (@as(u4, 1) << descriptor.dictionary_id_flag) >> 1;
break :d try in.takeVarInt(u32, .little, field_size);
} else null;
Test: build
const content_size: ?u64 = if (descriptor.single_segment_flag or descriptor.content_size_flag > 0) c: {
const field_size = @as(u4, 1) << descriptor.content_size_flag;
const content_size = try in.takeVarInt(u64, .little, field_size);
break :c if (field_size == 2) content_size + 256 else content_size;
} else null;
predefined_literal:
return .{
.descriptor = descriptor,
.window_descriptor = window_descriptor,
.dictionary_id = dictionary_id,
.content_size = content_size,
};
}
predefined_match:
/// Returns the window size required to decompress a frame, or `null` if it
/// cannot be determined (which indicates a malformed frame header).
pub fn windowSize(header: Header) ?u64 {
if (header.window_descriptor) |descriptor| {
const exponent = (descriptor & 0b11111000) >> 3;
const mantissa = descriptor & 0b00000111;
const window_log = 10 + exponent;
const window_base = @as(u64, 1) << @as(u6, @intCast(window_log));
const window_add = (window_base / 8) * mantissa;
return window_base + window_add;
} else return header.content_size;
}
};
predefined_offset:
pub const Block = struct {
pub const Header = packed struct(u24) {
last: bool,
type: Type,
size: u21,
};
pub const Type = enum(u2) {
raw,
rle,
compressed,
reserved,
};
};
pub const Decode = struct {
repeat_offsets: [3]u32,
offset: StateData(8),
match: StateData(9),
literal: StateData(9),
literal_fse_buffer: [zstd.table_size_max.literal]Table.Fse,
match_fse_buffer: [zstd.table_size_max.match]Table.Fse,
offset_fse_buffer: [zstd.table_size_max.offset]Table.Fse,
fse_tables_undefined: bool,
literal_stream_reader: ReverseBitReader,
literal_stream_index: usize,
literal_streams: LiteralsSection.Streams,
literal_header: LiteralsSection.Header,
huffman_tree: ?LiteralsSection.HuffmanTree,
literal_written_count: usize,
fn StateData(comptime max_accuracy_log: comptime_int) type {
return struct {
state: @This().State,
table: Table,
accuracy_log: u8,
const State = std.meta.Int(.unsigned, max_accuracy_log);
};
}
const init: Decode = .{
.repeat_offsets = .{
zstd.start_repeated_offset_1,
zstd.start_repeated_offset_2,
zstd.start_repeated_offset_3,
},
.offset = undefined,
.match = undefined,
.literal = undefined,
.literal_fse_buffer = undefined,
.match_fse_buffer = undefined,
.offset_fse_buffer = undefined,
.fse_tables_undefined = true,
.literal_written_count = 0,
.literal_header = undefined,
.literal_streams = undefined,
.literal_stream_reader = undefined,
.literal_stream_index = undefined,
.huffman_tree = null,
};
pub const PrepareError = error{
/// the (reversed) literal bitstream's first byte does not have any bits set
MissingStartBit,
/// `literals` is a treeless literals section and the decode state does not
/// have a Huffman tree from a previous block
TreelessLiteralsFirst,
/// on the first call if one of the sequence FSE tables is set to repeat mode
RepeatModeFirst,
/// an FSE table has an invalid accuracy
MalformedAccuracyLog,
/// failed decoding an FSE table
MalformedFseTable,
/// input stream ends before all FSE tables are read
EndOfStream,
ReadFailed,
InputBufferUndersize,
};
/// Prepare the decoder to decode a compressed block. Loads the
/// literals stream and Huffman tree from `literals` and reads the
/// FSE tables from `in`.
pub fn prepare(
self: *Decode,
in: *Reader,
remaining: *Limit,
literals: LiteralsSection,
sequences_header: SequencesSection.Header,
) PrepareError!void {
self.literal_written_count = 0;
self.literal_header = literals.header;
self.literal_streams = literals.streams;
if (literals.huffman_tree) |tree| {
self.huffman_tree = tree;
} else if (literals.header.block_type == .treeless and self.huffman_tree == null) {
return error.TreelessLiteralsFirst;
}
switch (literals.header.block_type) {
.raw, .rle => {},
.compressed, .treeless => {
self.literal_stream_index = 0;
switch (literals.streams) {
.one => |slice| try self.initLiteralStream(slice),
.four => |streams| try self.initLiteralStream(streams[0]),
}
},
}
if (sequences_header.sequence_count > 0) {
try self.updateFseTable(in, remaining, .literal, sequences_header.literal_lengths);
try self.updateFseTable(in, remaining, .offset, sequences_header.offsets);
try self.updateFseTable(in, remaining, .match, sequences_header.match_lengths);
self.fse_tables_undefined = false;
}
}
/// Read initial FSE states for sequence decoding.
pub fn readInitialFseState(self: *Decode, bit_reader: *ReverseBitReader) error{EndOfStream}!void {
self.literal.state = try bit_reader.readBitsNoEof(u9, self.literal.accuracy_log);
self.offset.state = try bit_reader.readBitsNoEof(u8, self.offset.accuracy_log);
self.match.state = try bit_reader.readBitsNoEof(u9, self.match.accuracy_log);
}
fn updateRepeatOffset(self: *Decode, offset: u32) void {
self.repeat_offsets[2] = self.repeat_offsets[1];
self.repeat_offsets[1] = self.repeat_offsets[0];
self.repeat_offsets[0] = offset;
}
fn useRepeatOffset(self: *Decode, index: usize) u32 {
if (index == 1)
std.mem.swap(u32, &self.repeat_offsets[0], &self.repeat_offsets[1])
else if (index == 2) {
std.mem.swap(u32, &self.repeat_offsets[0], &self.repeat_offsets[2]);
std.mem.swap(u32, &self.repeat_offsets[1], &self.repeat_offsets[2]);
}
return self.repeat_offsets[0];
}
const WhichFse = enum { offset, match, literal };
/// TODO: don't use `@field`
fn updateState(
self: *Decode,
comptime choice: WhichFse,
bit_reader: *ReverseBitReader,
) error{ MalformedFseBits, EndOfStream }!void {
switch (@field(self, @tagName(choice)).table) {
.rle => {},
.fse => |table| {
const data = table[@field(self, @tagName(choice)).state];
const T = @TypeOf(@field(self, @tagName(choice))).State;
const bits_summand = try bit_reader.readBitsNoEof(T, data.bits);
const next_state = std.math.cast(
@TypeOf(@field(self, @tagName(choice))).State,
data.baseline + bits_summand,
) orelse return error.MalformedFseBits;
@field(self, @tagName(choice)).state = next_state;
},
}
}
const FseTableError = error{
MalformedFseTable,
MalformedAccuracyLog,
RepeatModeFirst,
EndOfStream,
};
/// TODO: don't use `@field`
fn updateFseTable(
self: *Decode,
in: *Reader,
remaining: *Limit,
comptime choice: WhichFse,
mode: SequencesSection.Header.Mode,
) !void {
const field_name = @tagName(choice);
switch (mode) {
.predefined => {
@field(self, field_name).accuracy_log =
@field(zstd.default_accuracy_log, field_name);
@field(self, field_name).table =
@field(Table, "predefined_" ++ field_name);
},
.rle => {
@field(self, field_name).accuracy_log = 0;
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
@field(self, field_name).table = .{ .rle = try in.takeByte() };
},
.fse => {
const max_table_size = 2048;
const peek_len: usize = remaining.minInt(max_table_size);
if (in.buffer.len < peek_len) return error.InputBufferUndersize;
const limited_buffer = try in.peek(peek_len);
var bit_reader: BitReader = .{ .bytes = limited_buffer };
const table_size = try Table.decode(
&bit_reader,
@field(zstd.table_symbol_count_max, field_name),
@field(zstd.table_accuracy_log_max, field_name),
&@field(self, field_name ++ "_fse_buffer"),
);
@field(self, field_name).table = .{
.fse = (&@field(self, field_name ++ "_fse_buffer"))[0..table_size],
};
@field(self, field_name).accuracy_log = std.math.log2_int_ceil(usize, table_size);
in.toss(bit_reader.index);
remaining.* = remaining.subtract(bit_reader.index).?;
},
.repeat => if (self.fse_tables_undefined) return error.RepeatModeFirst,
}
}
const Sequence = struct {
literal_length: u32,
match_length: u32,
offset: u32,
};
fn nextSequence(
self: *Decode,
bit_reader: *ReverseBitReader,
) error{ InvalidBitStream, EndOfStream }!Sequence {
const raw_code = self.getCode(.offset);
const offset_code = std.math.cast(u5, raw_code) orelse {
return error.InvalidBitStream;
};
const offset_value = (@as(u32, 1) << offset_code) + try bit_reader.readBitsNoEof(u32, offset_code);
const match_code = self.getCode(.match);
if (match_code >= zstd.match_length_code_table.len)
return error.InvalidBitStream;
const match = zstd.match_length_code_table[match_code];
const match_length = match[0] + try bit_reader.readBitsNoEof(u32, match[1]);
const literal_code = self.getCode(.literal);
if (literal_code >= zstd.literals_length_code_table.len)
return error.InvalidBitStream;
const literal = zstd.literals_length_code_table[literal_code];
const literal_length = literal[0] + try bit_reader.readBitsNoEof(u32, literal[1]);
const offset = if (offset_value > 3) offset: {
const offset = offset_value - 3;
self.updateRepeatOffset(offset);
break :offset offset;
} else offset: {
if (literal_length == 0) {
if (offset_value == 3) {
const offset = self.repeat_offsets[0] - 1;
self.updateRepeatOffset(offset);
break :offset offset;
}
break :offset self.useRepeatOffset(offset_value);
}
break :offset self.useRepeatOffset(offset_value - 1);
};
if (offset == 0) return error.InvalidBitStream;
return .{
.literal_length = literal_length,
.match_length = match_length,
.offset = offset,
};
}
/// Decode one sequence from `bit_reader` into `dest`. Updates FSE states
/// if `last_sequence` is `false`. Assumes `prepare` called for the block
/// before attempting to decode sequences.
fn decodeSequence(
decode: *Decode,
dest: []u8,
write_pos: usize,
bit_reader: *ReverseBitReader,
) !usize {
const sequence = try decode.nextSequence(bit_reader);
const literal_length: usize = sequence.literal_length;
const match_length: usize = sequence.match_length;
const sequence_length = literal_length + match_length;
const copy_start = std.math.sub(usize, write_pos + sequence.literal_length, sequence.offset) catch
return error.MalformedSequence;
if (decode.literal_written_count + literal_length > decode.literal_header.regenerated_size)
return error.MalformedLiteralsLength;
var sub_bw: Writer = .fixed(dest[write_pos..]);
try decodeLiterals(decode, &sub_bw, literal_length);
decode.literal_written_count += literal_length;
// This is not a @memmove; it intentionally repeats patterns
// caused by iterating one byte at a time.
for (
dest[write_pos + literal_length ..][0..match_length],
dest[copy_start..][0..match_length],
) |*d, s| d.* = s;
return sequence_length;
}
fn nextLiteralMultiStream(self: *Decode) error{MissingStartBit}!void {
self.literal_stream_index += 1;
try self.initLiteralStream(self.literal_streams.four[self.literal_stream_index]);
}
fn initLiteralStream(self: *Decode, bytes: []const u8) error{MissingStartBit}!void {
self.literal_stream_reader = try ReverseBitReader.init(bytes);
}
fn isLiteralStreamEmpty(self: *Decode) bool {
switch (self.literal_streams) {
.one => return self.literal_stream_reader.isEmpty(),
.four => return self.literal_stream_index == 3 and self.literal_stream_reader.isEmpty(),
}
}
const LiteralBitsError = error{
MissingStartBit,
UnexpectedEndOfLiteralStream,
};
fn readLiteralsBits(
self: *Decode,
bit_count_to_read: u16,
) LiteralBitsError!u16 {
return self.literal_stream_reader.readBitsNoEof(u16, bit_count_to_read) catch bits: {
if (self.literal_streams == .four and self.literal_stream_index < 3) {
try self.nextLiteralMultiStream();
break :bits self.literal_stream_reader.readBitsNoEof(u16, bit_count_to_read) catch
return error.UnexpectedEndOfLiteralStream;
} else {
return error.UnexpectedEndOfLiteralStream;
}
};
}
/// Decode `len` bytes of literals into `w`.
fn decodeLiterals(d: *Decode, w: *Writer, len: usize) !void {
switch (d.literal_header.block_type) {
.raw => {
try w.writeAll(d.literal_streams.one[d.literal_written_count..][0..len]);
},
.rle => {
try w.splatByteAll(d.literal_streams.one[0], len);
},
.compressed, .treeless => {
if (len > w.buffer.len) return error.OutputBufferUndersize;
const buf = try w.writableSlice(len);
const huffman_tree = d.huffman_tree.?;
const max_bit_count = huffman_tree.max_bit_count;
const starting_bit_count = LiteralsSection.HuffmanTree.weightToBitCount(
huffman_tree.nodes[huffman_tree.symbol_count_minus_one].weight,
max_bit_count,
);
var bits_read: u4 = 0;
var huffman_tree_index: usize = huffman_tree.symbol_count_minus_one;
var bit_count_to_read: u4 = starting_bit_count;
for (buf) |*out| {
var prefix: u16 = 0;
while (true) {
const new_bits = try d.readLiteralsBits(bit_count_to_read);
prefix <<= bit_count_to_read;
prefix |= new_bits;
bits_read += bit_count_to_read;
const result = try huffman_tree.query(huffman_tree_index, prefix);
switch (result) {
.symbol => |sym| {
out.* = sym;
bit_count_to_read = starting_bit_count;
bits_read = 0;
huffman_tree_index = huffman_tree.symbol_count_minus_one;
break;
},
.index => |index| {
huffman_tree_index = index;
const bit_count = LiteralsSection.HuffmanTree.weightToBitCount(
huffman_tree.nodes[index].weight,
max_bit_count,
);
bit_count_to_read = bit_count - bits_read;
},
}
}
}
},
}
}
/// TODO: don't use `@field`
fn getCode(self: *Decode, comptime choice: WhichFse) u32 {
return switch (@field(self, @tagName(choice)).table) {
.rle => |value| value,
.fse => |table| table[@field(self, @tagName(choice)).state].symbol,
};
}
};
};
pub const Skippable = struct {
pub const magic_min: Magic = @enumFromInt(0x184D2A50);
pub const magic_max: Magic = @enumFromInt(0x184D2A5F);
pub const Header = struct {
magic_number: u32,
frame_size: u32,
};
};
const InitError = error{
/// Frame uses a dictionary.
DictionaryIdFlagUnsupported,
/// Frame does not have a valid window size.
WindowSizeUnknown,
/// Window size exceeds `window_size_max` or max `usize` value.
WindowOversize,
/// Frame header indicates a content size exceeding max `usize` value.
ContentOversize,
};
/// Validates `frame_header` and returns the associated `Frame`.
pub fn init(
frame_header: Frame.Zstandard.Header,
window_size_max: usize,
verify_checksum: bool,
) InitError!Frame {
if (frame_header.descriptor.dictionary_id_flag != 0)
return error.DictionaryIdFlagUnsupported;
const window_size_raw = frame_header.windowSize() orelse return error.WindowSizeUnknown;
const window_size = if (window_size_raw > window_size_max)
return error.WindowOversize
else
std.math.cast(usize, window_size_raw) orelse return error.WindowOversize;
const should_compute_checksum =
frame_header.descriptor.content_checksum_flag and verify_checksum;
const content_size = if (frame_header.content_size) |size|
std.math.cast(usize, size) orelse return error.ContentOversize
else
null;
return .{
.hasher_opt = if (should_compute_checksum) std.hash.XxHash64.init(0) else null,
.window_size = window_size,
.has_checksum = frame_header.descriptor.content_checksum_flag,
.block_size_max = @min(zstd.block_size_max, window_size),
.content_size = content_size,
};
}
};
pub const LiteralsSection = struct {
header: Header,
huffman_tree: ?HuffmanTree,
streams: Streams,
pub const Streams = union(enum) {
one: []const u8,
four: [4][]const u8,
fn decode(size_format: u2, stream_data: []const u8) !Streams {
if (size_format == 0) {
return .{ .one = stream_data };
}
if (stream_data.len < 6) return error.MalformedLiteralsSection;
const stream_1_length: usize = std.mem.readInt(u16, stream_data[0..2], .little);
const stream_2_length: usize = std.mem.readInt(u16, stream_data[2..4], .little);
const stream_3_length: usize = std.mem.readInt(u16, stream_data[4..6], .little);
const stream_1_start = 6;
const stream_2_start = stream_1_start + stream_1_length;
const stream_3_start = stream_2_start + stream_2_length;
const stream_4_start = stream_3_start + stream_3_length;
if (stream_data.len < stream_4_start) return error.MalformedLiteralsSection;
return .{ .four = .{
stream_data[stream_1_start .. stream_1_start + stream_1_length],
stream_data[stream_2_start .. stream_2_start + stream_2_length],
stream_data[stream_3_start .. stream_3_start + stream_3_length],
stream_data[stream_4_start..],
} };
}
};
pub const Header = struct {
block_type: BlockType,
size_format: u2,
regenerated_size: u20,
compressed_size: ?u18,
/// Decode a literals section header.
pub fn decode(in: *Reader, remaining: *Limit) !Header {
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
const byte0 = try in.takeByte();
const block_type: BlockType = @enumFromInt(byte0 & 0b11);
const size_format: u2 = @intCast((byte0 & 0b1100) >> 2);
var regenerated_size: u20 = undefined;
var compressed_size: ?u18 = null;
switch (block_type) {
.raw, .rle => {
switch (size_format) {
0, 2 => {
regenerated_size = byte0 >> 3;
},
1 => {
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
regenerated_size = (byte0 >> 4) + (@as(u20, try in.takeByte()) << 4);
},
3 => {
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
regenerated_size = (byte0 >> 4) +
(@as(u20, try in.takeByte()) << 4) +
(@as(u20, try in.takeByte()) << 12);
},
}
},
.compressed, .treeless => {
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
const byte1 = try in.takeByte();
const byte2 = try in.takeByte();
switch (size_format) {
0, 1 => {
regenerated_size = (byte0 >> 4) + ((@as(u20, byte1) & 0b00111111) << 4);
compressed_size = ((byte1 & 0b11000000) >> 6) + (@as(u18, byte2) << 2);
},
2 => {
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
const byte3 = try in.takeByte();
regenerated_size = (byte0 >> 4) + (@as(u20, byte1) << 4) + ((@as(u20, byte2) & 0b00000011) << 12);
compressed_size = ((byte2 & 0b11111100) >> 2) + (@as(u18, byte3) << 6);
},
3 => {
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
const byte3 = try in.takeByte();
const byte4 = try in.takeByte();
regenerated_size = (byte0 >> 4) + (@as(u20, byte1) << 4) + ((@as(u20, byte2) & 0b00111111) << 12);
compressed_size = ((byte2 & 0b11000000) >> 6) + (@as(u18, byte3) << 2) + (@as(u18, byte4) << 10);
},
}
},
}
return .{
.block_type = block_type,
.size_format = size_format,
.regenerated_size = regenerated_size,
.compressed_size = compressed_size,
};
}
};
pub const BlockType = enum(u2) {
raw,
rle,
compressed,
treeless,
};
pub const HuffmanTree = struct {
max_bit_count: u4,
symbol_count_minus_one: u8,
nodes: [256]PrefixedSymbol,
pub const PrefixedSymbol = struct {
symbol: u8,
prefix: u16,
weight: u4,
};
pub const Result = union(enum) {
symbol: u8,
index: usize,
};
pub fn query(self: HuffmanTree, index: usize, prefix: u16) error{HuffmanTreeIncomplete}!Result {
var node = self.nodes[index];
const weight = node.weight;
var i: usize = index;
while (node.weight == weight) {
if (node.prefix == prefix) return .{ .symbol = node.symbol };
if (i == 0) return error.HuffmanTreeIncomplete;
i -= 1;
node = self.nodes[i];
}
return .{ .index = i };
}
pub fn weightToBitCount(weight: u4, max_bit_count: u4) u4 {
return if (weight == 0) 0 else ((max_bit_count + 1) - weight);
}
pub const DecodeError = Reader.Error || error{
MalformedHuffmanTree,
MalformedFseTable,
MalformedAccuracyLog,
EndOfStream,
MissingStartBit,
};
pub fn decode(in: *Reader, remaining: *Limit) HuffmanTree.DecodeError!HuffmanTree {
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
const header = try in.takeByte();
if (header < 128) {
return decodeFse(in, remaining, header);
} else {
return decodeDirect(in, remaining, header - 127);
}
}
fn decodeDirect(
in: *Reader,
remaining: *Limit,
encoded_symbol_count: usize,
) HuffmanTree.DecodeError!HuffmanTree {
var weights: [256]u4 = undefined;
const weights_byte_count = (encoded_symbol_count + 1) / 2;
remaining.* = remaining.subtract(weights_byte_count) orelse return error.EndOfStream;
for (0..weights_byte_count) |i| {
const byte = try in.takeByte();
weights[2 * i] = @as(u4, @intCast(byte >> 4));
weights[2 * i + 1] = @as(u4, @intCast(byte & 0xF));
}
const symbol_count = encoded_symbol_count + 1;
return build(&weights, symbol_count);
}
fn decodeFse(
in: *Reader,
remaining: *Limit,
compressed_size: usize,
) HuffmanTree.DecodeError!HuffmanTree {
var weights: [256]u4 = undefined;
remaining.* = remaining.subtract(compressed_size) orelse return error.EndOfStream;
const compressed_buffer = try in.take(compressed_size);
var bit_reader: BitReader = .{ .bytes = compressed_buffer };
var entries: [1 << 6]Table.Fse = undefined;
const table_size = try Table.decode(&bit_reader, 256, 6, &entries);
const accuracy_log = std.math.log2_int_ceil(usize, table_size);
const remaining_buffer = bit_reader.bytes[bit_reader.index..];
const symbol_count = try assignWeights(remaining_buffer, accuracy_log, &entries, &weights);
return build(&weights, symbol_count);
}
fn assignWeights(
huff_bits_buffer: []const u8,
accuracy_log: u16,
entries: *[1 << 6]Table.Fse,
weights: *[256]u4,
) !usize {
var huff_bits = try ReverseBitReader.init(huff_bits_buffer);
var i: usize = 0;
var even_state: u32 = try huff_bits.readBitsNoEof(u32, accuracy_log);
var odd_state: u32 = try huff_bits.readBitsNoEof(u32, accuracy_log);
while (i < 254) {
const even_data = entries[even_state];
var read_bits: u16 = 0;
const even_bits = huff_bits.readBits(u32, even_data.bits, &read_bits) catch unreachable;
weights[i] = std.math.cast(u4, even_data.symbol) orelse return error.MalformedHuffmanTree;
i += 1;
if (read_bits < even_data.bits) {
weights[i] = std.math.cast(u4, entries[odd_state].symbol) orelse return error.MalformedHuffmanTree;
i += 1;
break;
}
even_state = even_data.baseline + even_bits;
read_bits = 0;
const odd_data = entries[odd_state];
const odd_bits = huff_bits.readBits(u32, odd_data.bits, &read_bits) catch unreachable;
weights[i] = std.math.cast(u4, odd_data.symbol) orelse return error.MalformedHuffmanTree;
i += 1;
if (read_bits < odd_data.bits) {
if (i == 255) return error.MalformedHuffmanTree;
weights[i] = std.math.cast(u4, entries[even_state].symbol) orelse return error.MalformedHuffmanTree;
i += 1;
break;
}
odd_state = odd_data.baseline + odd_bits;
} else return error.MalformedHuffmanTree;
if (!huff_bits.isEmpty()) {
return error.MalformedHuffmanTree;
}
return i + 1; // stream contains all but the last symbol
}
fn assignSymbols(weight_sorted_prefixed_symbols: []PrefixedSymbol, weights: [256]u4) usize {
for (0..weight_sorted_prefixed_symbols.len) |i| {
weight_sorted_prefixed_symbols[i] = .{
.symbol = @as(u8, @intCast(i)),
.weight = undefined,
.prefix = undefined,
};
}
std.mem.sort(
PrefixedSymbol,
weight_sorted_prefixed_symbols,
weights,
lessThanByWeight,
);
var prefix: u16 = 0;
var prefixed_symbol_count: usize = 0;
var sorted_index: usize = 0;
const symbol_count = weight_sorted_prefixed_symbols.len;
while (sorted_index < symbol_count) {
var symbol = weight_sorted_prefixed_symbols[sorted_index].symbol;
const weight = weights[symbol];
if (weight == 0) {
sorted_index += 1;
continue;
}
while (sorted_index < symbol_count) : ({
sorted_index += 1;
prefixed_symbol_count += 1;
prefix += 1;
}) {
symbol = weight_sorted_prefixed_symbols[sorted_index].symbol;
if (weights[symbol] != weight) {
prefix = ((prefix - 1) >> (weights[symbol] - weight)) + 1;
break;
}
weight_sorted_prefixed_symbols[prefixed_symbol_count].symbol = symbol;
weight_sorted_prefixed_symbols[prefixed_symbol_count].prefix = prefix;
weight_sorted_prefixed_symbols[prefixed_symbol_count].weight = weight;
}
}
return prefixed_symbol_count;
}
fn build(weights: *[256]u4, symbol_count: usize) error{MalformedHuffmanTree}!HuffmanTree {
var weight_power_sum_big: u32 = 0;
for (weights[0 .. symbol_count - 1]) |value| {
weight_power_sum_big += (@as(u16, 1) << value) >> 1;
}
if (weight_power_sum_big >= 1 << 11) return error.MalformedHuffmanTree;
const weight_power_sum = @as(u16, @intCast(weight_power_sum_big));
// advance to next power of two (even if weight_power_sum is a power of 2)
// TODO: is it valid to have weight_power_sum == 0?
const max_number_of_bits = if (weight_power_sum == 0) 1 else std.math.log2_int(u16, weight_power_sum) + 1;
const next_power_of_two = @as(u16, 1) << max_number_of_bits;
weights[symbol_count - 1] = std.math.log2_int(u16, next_power_of_two - weight_power_sum) + 1;
var weight_sorted_prefixed_symbols: [256]PrefixedSymbol = undefined;
const prefixed_symbol_count = assignSymbols(weight_sorted_prefixed_symbols[0..symbol_count], weights.*);
const tree: HuffmanTree = .{
.max_bit_count = max_number_of_bits,
.symbol_count_minus_one = @as(u8, @intCast(prefixed_symbol_count - 1)),
.nodes = weight_sorted_prefixed_symbols,
};
return tree;
}
fn lessThanByWeight(
weights: [256]u4,
lhs: PrefixedSymbol,
rhs: PrefixedSymbol,
) bool {
// NOTE: this function relies on the use of a stable sorting algorithm,
// otherwise a special case of if (weights[lhs] == weights[rhs]) return lhs < rhs;
// should be added
return weights[lhs.symbol] < weights[rhs.symbol];
}
};
pub const StreamCount = enum { one, four };
pub fn streamCount(size_format: u2, block_type: BlockType) StreamCount {
return switch (block_type) {
.raw, .rle => .one,
.compressed, .treeless => if (size_format == 0) .one else .four,
};
}
pub const DecodeError = error{
/// Invalid header.
MalformedLiteralsHeader,
/// Decoding errors.
MalformedLiteralsSection,
/// Compressed literals have invalid accuracy.
MalformedAccuracyLog,
/// Compressed literals have invalid FSE table.
MalformedFseTable,
/// Failed decoding a Huffamn tree.
MalformedHuffmanTree,
/// Not enough bytes to complete the section.
EndOfStream,
ReadFailed,
MissingStartBit,
};
pub fn decode(in: *Reader, remaining: *Limit, buffer: []u8) DecodeError!LiteralsSection {
const header = try Header.decode(in, remaining);
switch (header.block_type) {
.raw => {
if (buffer.len < header.regenerated_size) return error.MalformedLiteralsSection;
remaining.* = remaining.subtract(header.regenerated_size) orelse return error.EndOfStream;
try in.readSliceAll(buffer[0..header.regenerated_size]);
return .{
.header = header,
.huffman_tree = null,
.streams = .{ .one = buffer },
};
},
.rle => {
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
buffer[0] = try in.takeByte();
return .{
.header = header,
.huffman_tree = null,
.streams = .{ .one = buffer[0..1] },
};
},
.compressed, .treeless => {
const before_remaining = remaining.*;
const huffman_tree = if (header.block_type == .compressed)
try HuffmanTree.decode(in, remaining)
else
null;
const huffman_tree_size = @intFromEnum(before_remaining) - @intFromEnum(remaining.*);
const total_streams_size = std.math.sub(usize, header.compressed_size.?, huffman_tree_size) catch
return error.MalformedLiteralsSection;
if (total_streams_size > buffer.len) return error.MalformedLiteralsSection;
remaining.* = remaining.subtract(total_streams_size) orelse return error.EndOfStream;
try in.readSliceAll(buffer[0..total_streams_size]);
const stream_data = buffer[0..total_streams_size];
const streams = try Streams.decode(header.size_format, stream_data);
return .{
.header = header,
.huffman_tree = huffman_tree,
.streams = streams,
};
},
}
}
};
pub const SequencesSection = struct {
header: Header,
literals_length_table: Table,
offset_table: Table,
match_length_table: Table,
pub const Header = struct {
sequence_count: u24,
match_lengths: Mode,
offsets: Mode,
literal_lengths: Mode,
pub const Mode = enum(u2) {
predefined,
rle,
fse,
repeat,
};
pub const DecodeError = error{
ReservedBitSet,
EndOfStream,
ReadFailed,
};
pub fn decode(in: *Reader, remaining: *Limit) DecodeError!Header {
var sequence_count: u24 = undefined;
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
const byte0 = try in.takeByte();
if (byte0 == 0) {
return .{
.sequence_count = 0,
.offsets = undefined,
.match_lengths = undefined,
.literal_lengths = undefined,
};
} else if (byte0 < 128) {
remaining.* = remaining.subtract(1) orelse return error.EndOfStream;
sequence_count = byte0;
} else if (byte0 < 255) {
remaining.* = remaining.subtract(2) orelse return error.EndOfStream;
sequence_count = (@as(u24, (byte0 - 128)) << 8) + try in.takeByte();
} else {
remaining.* = remaining.subtract(3) orelse return error.EndOfStream;
sequence_count = (try in.takeByte()) + (@as(u24, try in.takeByte()) << 8) + 0x7F00;
}
const compression_modes = try in.takeByte();
const matches_mode: Header.Mode = @enumFromInt((compression_modes & 0b00001100) >> 2);
const offsets_mode: Header.Mode = @enumFromInt((compression_modes & 0b00110000) >> 4);
const literal_mode: Header.Mode = @enumFromInt((compression_modes & 0b11000000) >> 6);
if (compression_modes & 0b11 != 0) return error.ReservedBitSet;
return .{
.sequence_count = sequence_count,
.offsets = offsets_mode,
.match_lengths = matches_mode,
.literal_lengths = literal_mode,
};
}
};
};
pub const Table = union(enum) {
fse: []const Fse,
rle: u8,
pub const Fse = struct {
symbol: u8,
baseline: u16,
bits: u8,
};
pub fn decode(
bit_reader: *BitReader,
expected_symbol_count: usize,
max_accuracy_log: u4,
entries: []Table.Fse,
) !usize {
const accuracy_log_biased = try bit_reader.readBitsNoEof(u4, 4);
if (accuracy_log_biased > max_accuracy_log -| 5) return error.MalformedAccuracyLog;
const accuracy_log = accuracy_log_biased + 5;
var values: [256]u16 = undefined;
var value_count: usize = 0;
const total_probability = @as(u16, 1) << accuracy_log;
var accumulated_probability: u16 = 0;
while (accumulated_probability < total_probability) {
// WARNING: The RFC is poorly worded, and would suggest std.math.log2_int_ceil is correct here,
// but power of two (remaining probabilities + 1) need max bits set to 1 more.
const max_bits = std.math.log2_int(u16, total_probability - accumulated_probability + 1) + 1;
const small = try bit_reader.readBitsNoEof(u16, max_bits - 1);
const cutoff = (@as(u16, 1) << max_bits) - 1 - (total_probability - accumulated_probability + 1);
const value = if (small < cutoff)
small
else value: {
const value_read = small + (try bit_reader.readBitsNoEof(u16, 1) << (max_bits - 1));
break :value if (value_read < @as(u16, 1) << (max_bits - 1))
value_read
else
value_read - cutoff;
};
accumulated_probability += if (value != 0) value - 1 else 1;
values[value_count] = value;
value_count += 1;
if (value == 1) {
while (true) {
const repeat_flag = try bit_reader.readBitsNoEof(u2, 2);
if (repeat_flag + value_count > 256) return error.MalformedFseTable;
for (0..repeat_flag) |_| {
values[value_count] = 1;
value_count += 1;
}
if (repeat_flag < 3) break;
}
}
if (value_count == 256) break;
}
bit_reader.alignToByte();
if (value_count < 2) return error.MalformedFseTable;
if (accumulated_probability != total_probability) return error.MalformedFseTable;
if (value_count > expected_symbol_count) return error.MalformedFseTable;
const table_size = total_probability;
try build(values[0..value_count], entries[0..table_size]);
return table_size;
}
pub fn build(values: []const u16, entries: []Table.Fse) !void {
const total_probability = @as(u16, @intCast(entries.len));
const accuracy_log = std.math.log2_int(u16, total_probability);
assert(total_probability <= 1 << 9);
var less_than_one_count: usize = 0;
for (values, 0..) |value, i| {
if (value == 0) {
entries[entries.len - 1 - less_than_one_count] = Table.Fse{
.symbol = @as(u8, @intCast(i)),
.baseline = 0,
.bits = accuracy_log,
};
less_than_one_count += 1;
}
}
var position: usize = 0;
var temp_states: [1 << 9]u16 = undefined;
for (values, 0..) |value, symbol| {
if (value == 0 or value == 1) continue;
const probability = value - 1;
const state_share_dividend = std.math.ceilPowerOfTwo(u16, probability) catch
return error.MalformedFseTable;
const share_size = @divExact(total_probability, state_share_dividend);
const double_state_count = state_share_dividend - probability;
const single_state_count = probability - double_state_count;
const share_size_log = std.math.log2_int(u16, share_size);
for (0..probability) |i| {
temp_states[i] = @as(u16, @intCast(position));
position += (entries.len >> 1) + (entries.len >> 3) + 3;
position &= entries.len - 1;
while (position >= entries.len - less_than_one_count) {
position += (entries.len >> 1) + (entries.len >> 3) + 3;
position &= entries.len - 1;
}
}
std.mem.sort(u16, temp_states[0..probability], {}, std.sort.asc(u16));
for (0..probability) |i| {
entries[temp_states[i]] = if (i < double_state_count) Table.Fse{
.symbol = @as(u8, @intCast(symbol)),
.bits = share_size_log + 1,
.baseline = single_state_count * share_size + @as(u16, @intCast(i)) * 2 * share_size,
} else Table.Fse{
.symbol = @as(u8, @intCast(symbol)),
.bits = share_size_log,
.baseline = (@as(u16, @intCast(i)) - double_state_count) * share_size,
};
}
}
}
test build {
const literals_length_default_values = [36]u16{
5, 4, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 2, 2, 2,
3, 3, 3, 3, 3, 3, 3, 3, 3, 4, 3, 2, 2, 2, 2, 2,
0, 0, 0, 0,
};
const match_lengths_default_values = [53]u16{
2, 5, 4, 3, 3, 3, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 0, 0,
0, 0, 0, 0, 0,
};
const offset_codes_default_values = [29]u16{
2, 2, 2, 2, 2, 2, 3, 3, 3, 2, 2, 2, 2, 2, 2, 2,
2, 2, 2, 2, 2, 2, 2, 2, 0, 0, 0, 0, 0,
};
var entries: [64]Table.Fse = undefined;
try build(&literals_length_default_values, &entries);
try std.testing.expectEqualSlices(Table.Fse, Table.predefined_literal.fse, &entries);
try build(&match_lengths_default_values, &entries);
try std.testing.expectEqualSlices(Table.Fse, Table.predefined_match.fse, &entries);
try build(&offset_codes_default_values, entries[0..32]);
try std.testing.expectEqualSlices(Table.Fse, Table.predefined_offset.fse, entries[0..32]);
}
pub const predefined_literal: Table = .{
.fse = &[64]Table.Fse{
.{ .symbol = 0, .bits = 4, .baseline = 0 },
.{ .symbol = 0, .bits = 4, .baseline = 16 },
.{ .symbol = 1, .bits = 5, .baseline = 32 },
.{ .symbol = 3, .bits = 5, .baseline = 0 },
.{ .symbol = 4, .bits = 5, .baseline = 0 },
.{ .symbol = 6, .bits = 5, .baseline = 0 },
.{ .symbol = 7, .bits = 5, .baseline = 0 },
.{ .symbol = 9, .bits = 5, .baseline = 0 },
.{ .symbol = 10, .bits = 5, .baseline = 0 },
.{ .symbol = 12, .bits = 5, .baseline = 0 },
.{ .symbol = 14, .bits = 6, .baseline = 0 },
.{ .symbol = 16, .bits = 5, .baseline = 0 },
.{ .symbol = 18, .bits = 5, .baseline = 0 },
.{ .symbol = 19, .bits = 5, .baseline = 0 },
.{ .symbol = 21, .bits = 5, .baseline = 0 },
.{ .symbol = 22, .bits = 5, .baseline = 0 },
.{ .symbol = 24, .bits = 5, .baseline = 0 },
.{ .symbol = 25, .bits = 5, .baseline = 32 },
.{ .symbol = 26, .bits = 5, .baseline = 0 },
.{ .symbol = 27, .bits = 6, .baseline = 0 },
.{ .symbol = 29, .bits = 6, .baseline = 0 },
.{ .symbol = 31, .bits = 6, .baseline = 0 },
.{ .symbol = 0, .bits = 4, .baseline = 32 },
.{ .symbol = 1, .bits = 4, .baseline = 0 },
.{ .symbol = 2, .bits = 5, .baseline = 0 },
.{ .symbol = 4, .bits = 5, .baseline = 32 },
.{ .symbol = 5, .bits = 5, .baseline = 0 },
.{ .symbol = 7, .bits = 5, .baseline = 32 },
.{ .symbol = 8, .bits = 5, .baseline = 0 },
.{ .symbol = 10, .bits = 5, .baseline = 32 },
.{ .symbol = 11, .bits = 5, .baseline = 0 },
.{ .symbol = 13, .bits = 6, .baseline = 0 },
.{ .symbol = 16, .bits = 5, .baseline = 32 },
.{ .symbol = 17, .bits = 5, .baseline = 0 },
.{ .symbol = 19, .bits = 5, .baseline = 32 },
.{ .symbol = 20, .bits = 5, .baseline = 0 },
.{ .symbol = 22, .bits = 5, .baseline = 32 },
.{ .symbol = 23, .bits = 5, .baseline = 0 },
.{ .symbol = 25, .bits = 4, .baseline = 0 },
.{ .symbol = 25, .bits = 4, .baseline = 16 },
.{ .symbol = 26, .bits = 5, .baseline = 32 },
.{ .symbol = 28, .bits = 6, .baseline = 0 },
.{ .symbol = 30, .bits = 6, .baseline = 0 },
.{ .symbol = 0, .bits = 4, .baseline = 48 },
.{ .symbol = 1, .bits = 4, .baseline = 16 },
.{ .symbol = 2, .bits = 5, .baseline = 32 },
.{ .symbol = 3, .bits = 5, .baseline = 32 },
.{ .symbol = 5, .bits = 5, .baseline = 32 },
.{ .symbol = 6, .bits = 5, .baseline = 32 },
.{ .symbol = 8, .bits = 5, .baseline = 32 },
.{ .symbol = 9, .bits = 5, .baseline = 32 },
.{ .symbol = 11, .bits = 5, .baseline = 32 },
.{ .symbol = 12, .bits = 5, .baseline = 32 },
.{ .symbol = 15, .bits = 6, .baseline = 0 },
.{ .symbol = 17, .bits = 5, .baseline = 32 },
.{ .symbol = 18, .bits = 5, .baseline = 32 },
.{ .symbol = 20, .bits = 5, .baseline = 32 },
.{ .symbol = 21, .bits = 5, .baseline = 32 },
.{ .symbol = 23, .bits = 5, .baseline = 32 },
.{ .symbol = 24, .bits = 5, .baseline = 32 },
.{ .symbol = 35, .bits = 6, .baseline = 0 },
.{ .symbol = 34, .bits = 6, .baseline = 0 },
.{ .symbol = 33, .bits = 6, .baseline = 0 },
.{ .symbol = 32, .bits = 6, .baseline = 0 },
},
};
pub const predefined_match: Table = .{
.fse = &[64]Table.Fse{
.{ .symbol = 0, .bits = 6, .baseline = 0 },
.{ .symbol = 1, .bits = 4, .baseline = 0 },
.{ .symbol = 2, .bits = 5, .baseline = 32 },
.{ .symbol = 3, .bits = 5, .baseline = 0 },
.{ .symbol = 5, .bits = 5, .baseline = 0 },
.{ .symbol = 6, .bits = 5, .baseline = 0 },
.{ .symbol = 8, .bits = 5, .baseline = 0 },
.{ .symbol = 10, .bits = 6, .baseline = 0 },
.{ .symbol = 13, .bits = 6, .baseline = 0 },
.{ .symbol = 16, .bits = 6, .baseline = 0 },
.{ .symbol = 19, .bits = 6, .baseline = 0 },
.{ .symbol = 22, .bits = 6, .baseline = 0 },
.{ .symbol = 25, .bits = 6, .baseline = 0 },
.{ .symbol = 28, .bits = 6, .baseline = 0 },
.{ .symbol = 31, .bits = 6, .baseline = 0 },
.{ .symbol = 33, .bits = 6, .baseline = 0 },
.{ .symbol = 35, .bits = 6, .baseline = 0 },
.{ .symbol = 37, .bits = 6, .baseline = 0 },
.{ .symbol = 39, .bits = 6, .baseline = 0 },
.{ .symbol = 41, .bits = 6, .baseline = 0 },
.{ .symbol = 43, .bits = 6, .baseline = 0 },
.{ .symbol = 45, .bits = 6, .baseline = 0 },
.{ .symbol = 1, .bits = 4, .baseline = 16 },
.{ .symbol = 2, .bits = 4, .baseline = 0 },
.{ .symbol = 3, .bits = 5, .baseline = 32 },
.{ .symbol = 4, .bits = 5, .baseline = 0 },
.{ .symbol = 6, .bits = 5, .baseline = 32 },
.{ .symbol = 7, .bits = 5, .baseline = 0 },
.{ .symbol = 9, .bits = 6, .baseline = 0 },
.{ .symbol = 12, .bits = 6, .baseline = 0 },
.{ .symbol = 15, .bits = 6, .baseline = 0 },
.{ .symbol = 18, .bits = 6, .baseline = 0 },
.{ .symbol = 21, .bits = 6, .baseline = 0 },
.{ .symbol = 24, .bits = 6, .baseline = 0 },
.{ .symbol = 27, .bits = 6, .baseline = 0 },
.{ .symbol = 30, .bits = 6, .baseline = 0 },
.{ .symbol = 32, .bits = 6, .baseline = 0 },
.{ .symbol = 34, .bits = 6, .baseline = 0 },
.{ .symbol = 36, .bits = 6, .baseline = 0 },
.{ .symbol = 38, .bits = 6, .baseline = 0 },
.{ .symbol = 40, .bits = 6, .baseline = 0 },
.{ .symbol = 42, .bits = 6, .baseline = 0 },
.{ .symbol = 44, .bits = 6, .baseline = 0 },
.{ .symbol = 1, .bits = 4, .baseline = 32 },
.{ .symbol = 1, .bits = 4, .baseline = 48 },
.{ .symbol = 2, .bits = 4, .baseline = 16 },
.{ .symbol = 4, .bits = 5, .baseline = 32 },
.{ .symbol = 5, .bits = 5, .baseline = 32 },
.{ .symbol = 7, .bits = 5, .baseline = 32 },
.{ .symbol = 8, .bits = 5, .baseline = 32 },
.{ .symbol = 11, .bits = 6, .baseline = 0 },
.{ .symbol = 14, .bits = 6, .baseline = 0 },
.{ .symbol = 17, .bits = 6, .baseline = 0 },
.{ .symbol = 20, .bits = 6, .baseline = 0 },
.{ .symbol = 23, .bits = 6, .baseline = 0 },
.{ .symbol = 26, .bits = 6, .baseline = 0 },
.{ .symbol = 29, .bits = 6, .baseline = 0 },
.{ .symbol = 52, .bits = 6, .baseline = 0 },
.{ .symbol = 51, .bits = 6, .baseline = 0 },
.{ .symbol = 50, .bits = 6, .baseline = 0 },
.{ .symbol = 49, .bits = 6, .baseline = 0 },
.{ .symbol = 48, .bits = 6, .baseline = 0 },
.{ .symbol = 47, .bits = 6, .baseline = 0 },
.{ .symbol = 46, .bits = 6, .baseline = 0 },
},
};
pub const predefined_offset: Table = .{
.fse = &[32]Table.Fse{
.{ .symbol = 0, .bits = 5, .baseline = 0 },
.{ .symbol = 6, .bits = 4, .baseline = 0 },
.{ .symbol = 9, .bits = 5, .baseline = 0 },
.{ .symbol = 15, .bits = 5, .baseline = 0 },
.{ .symbol = 21, .bits = 5, .baseline = 0 },
.{ .symbol = 3, .bits = 5, .baseline = 0 },
.{ .symbol = 7, .bits = 4, .baseline = 0 },
.{ .symbol = 12, .bits = 5, .baseline = 0 },
.{ .symbol = 18, .bits = 5, .baseline = 0 },
.{ .symbol = 23, .bits = 5, .baseline = 0 },
.{ .symbol = 5, .bits = 5, .baseline = 0 },
.{ .symbol = 8, .bits = 4, .baseline = 0 },
.{ .symbol = 14, .bits = 5, .baseline = 0 },
.{ .symbol = 20, .bits = 5, .baseline = 0 },
.{ .symbol = 2, .bits = 5, .baseline = 0 },
.{ .symbol = 7, .bits = 4, .baseline = 16 },
.{ .symbol = 11, .bits = 5, .baseline = 0 },
.{ .symbol = 17, .bits = 5, .baseline = 0 },
.{ .symbol = 22, .bits = 5, .baseline = 0 },
.{ .symbol = 4, .bits = 5, .baseline = 0 },
.{ .symbol = 8, .bits = 4, .baseline = 16 },
.{ .symbol = 13, .bits = 5, .baseline = 0 },
.{ .symbol = 19, .bits = 5, .baseline = 0 },
.{ .symbol = 1, .bits = 5, .baseline = 0 },
.{ .symbol = 6, .bits = 4, .baseline = 16 },
.{ .symbol = 10, .bits = 5, .baseline = 0 },
.{ .symbol = 16, .bits = 5, .baseline = 0 },
.{ .symbol = 28, .bits = 5, .baseline = 0 },
.{ .symbol = 27, .bits = 5, .baseline = 0 },
.{ .symbol = 26, .bits = 5, .baseline = 0 },
.{ .symbol = 25, .bits = 5, .baseline = 0 },
.{ .symbol = 24, .bits = 5, .baseline = 0 },
},
};
};
const low_bit_mask = [9]u8{
0b00000000,
0b00000001,
0b00000011,
0b00000111,
0b00001111,
0b00011111,
0b00111111,
0b01111111,
0b11111111,
};
fn Bits(comptime T: type) type {
return struct { T, u16 };
}
/// For reading the reversed bit streams used to encode FSE compressed data.
const ReverseBitReader = struct {
bytes: []const u8,
remaining: usize,
bits: u8,
count: u4,
fn init(bytes: []const u8) error{MissingStartBit}!ReverseBitReader {
var result: ReverseBitReader = .{
.bytes = bytes,
.remaining = bytes.len,
.bits = 0,
.count = 0,
};
if (bytes.len == 0) return result;
for (0..8) |_| if (0 != (result.readBitsNoEof(u1, 1) catch unreachable)) return result;
return error.MissingStartBit;
}
fn initBits(comptime T: type, out: anytype, num: u16) Bits(T) {
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
return .{
@bitCast(@as(UT, @intCast(out))),
num,
};
}
fn readBitsNoEof(self: *ReverseBitReader, comptime T: type, num: u16) error{EndOfStream}!T {
const b, const c = try self.readBitsTuple(T, num);
if (c < num) return error.EndOfStream;
return b;
}
fn readBits(self: *ReverseBitReader, comptime T: type, num: u16, out_bits: *u16) !T {
const b, const c = try self.readBitsTuple(T, num);
out_bits.* = c;
return b;
}
fn readBitsTuple(self: *ReverseBitReader, comptime T: type, num: u16) !Bits(T) {
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
const U = if (@bitSizeOf(T) < 8) u8 else UT;
if (num <= self.count) return initBits(T, self.removeBits(@intCast(num)), num);
var out_count: u16 = self.count;
var out: U = self.removeBits(self.count);
const full_bytes_left = (num - out_count) / 8;
for (0..full_bytes_left) |_| {
const byte = takeByte(self) catch |err| switch (err) {
error.EndOfStream => return initBits(T, out, out_count),
};
if (U == u8) out = 0 else out <<= 8;
out |= byte;
out_count += 8;
}
const bits_left = num - out_count;
const keep = 8 - bits_left;
if (bits_left == 0) return initBits(T, out, out_count);
const final_byte = takeByte(self) catch |err| switch (err) {
error.EndOfStream => return initBits(T, out, out_count),
};
out <<= @intCast(bits_left);
out |= final_byte >> @intCast(keep);
self.bits = final_byte & low_bit_mask[keep];
self.count = @intCast(keep);
return initBits(T, out, num);
}
fn takeByte(rbr: *ReverseBitReader) error{EndOfStream}!u8 {
if (rbr.remaining == 0) return error.EndOfStream;
rbr.remaining -= 1;
return rbr.bytes[rbr.remaining];
}
fn isEmpty(self: *const ReverseBitReader) bool {
return self.remaining == 0 and self.count == 0;
}
fn removeBits(self: *ReverseBitReader, num: u4) u8 {
if (num == 8) {
self.count = 0;
return self.bits;
}
const keep = self.count - num;
const bits = self.bits >> @intCast(keep);
self.bits &= low_bit_mask[keep];
self.count = keep;
return bits;
}
};
const BitReader = struct {
bytes: []const u8,
index: usize = 0,
bits: u8 = 0,
count: u4 = 0,
fn initBits(comptime T: type, out: anytype, num: u16) Bits(T) {
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
return .{
@bitCast(@as(UT, @intCast(out))),
num,
};
}
fn readBitsNoEof(self: *@This(), comptime T: type, num: u16) !T {
const b, const c = try self.readBitsTuple(T, num);
if (c < num) return error.EndOfStream;
return b;
}
fn readBits(self: *@This(), comptime T: type, num: u16, out_bits: *u16) !T {
const b, const c = try self.readBitsTuple(T, num);
out_bits.* = c;
return b;
}
fn readBitsTuple(self: *@This(), comptime T: type, num: u16) !Bits(T) {
const UT = std.meta.Int(.unsigned, @bitSizeOf(T));
const U = if (@bitSizeOf(T) < 8) u8 else UT;
if (num <= self.count) return initBits(T, self.removeBits(@intCast(num)), num);
var out_count: u16 = self.count;
var out: U = self.removeBits(self.count);
const full_bytes_left = (num - out_count) / 8;
for (0..full_bytes_left) |_| {
const byte = takeByte(self) catch |err| switch (err) {
error.EndOfStream => return initBits(T, out, out_count),
};
const pos = @as(U, byte) << @intCast(out_count);
out |= pos;
out_count += 8;
}
const bits_left = num - out_count;
const keep = 8 - bits_left;
if (bits_left == 0) return initBits(T, out, out_count);
const final_byte = takeByte(self) catch |err| switch (err) {
error.EndOfStream => return initBits(T, out, out_count),
};
const pos = @as(U, final_byte & low_bit_mask[bits_left]) << @intCast(out_count);
out |= pos;
self.bits = final_byte >> @intCast(bits_left);
self.count = @intCast(keep);
return initBits(T, out, num);
}
fn takeByte(br: *BitReader) error{EndOfStream}!u8 {
if (br.bytes.len - br.index == 0) return error.EndOfStream;
const result = br.bytes[br.index];
br.index += 1;
return result;
}
fn removeBits(self: *@This(), num: u4) u8 {
if (num == 8) {
self.count = 0;
return self.bits;
}
const keep = self.count - num;
const bits = self.bits & low_bit_mask[num];
self.bits >>= @intCast(num);
self.count = keep;
return bits;
}
fn alignToByte(self: *@This()) void {
self.bits = 0;
self.count = 0;
}
};
test {
_ = Table;
}