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// There are two implementations of CRC32 implemented with the following key characteristics:
//
// - Crc32WithPoly uses 8Kb of tables but is ~10x faster than the small method.
//
// - Crc32SmallWithPoly uses only 64 bytes of memory but is slower. Be aware that this is
// still moderately fast just slow relative to the slicing approach.
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Algorithm()
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const std = @import("../std.zig");
const builtin = @import("builtin");
const debug = std.debug;
const testing = std.testing;
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Crc()
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pub usingnamespace @import("crc/catalog.zig");
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init()
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pub fn Algorithm(comptime W: type) type {
return struct {
polynomial: W,
initial: W,
reflect_input: bool,
reflect_output: bool,
xor_output: W,
};
}
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update()
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pub fn Crc(comptime W: type, comptime algorithm: Algorithm(W)) type {
return struct {
const Self = @This();
const I = if (@bitSizeOf(W) < 8) u8 else W;
const lookup_table = blk: {
@setEvalBranchQuota(2500);
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final()
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const poly = if (algorithm.reflect_input)
@bitReverse(@as(I, algorithm.polynomial)) >> (@bitSizeOf(I) - @bitSizeOf(W))
else
@as(I, algorithm.polynomial) << (@bitSizeOf(I) - @bitSizeOf(W));
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hash()
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var table: [256]I = undefined;
for (&table, 0..) |*e, i| {
var crc: I = i;
if (algorithm.reflect_input) {
var j: usize = 0;
while (j < 8) : (j += 1) {
crc = (crc >> 1) ^ ((crc & 1) * poly);
}
} else {
crc <<= @bitSizeOf(I) - 8;
var j: usize = 0;
while (j < 8) : (j += 1) {
crc = (crc << 1) ^ (((crc >> (@bitSizeOf(I) - 1)) & 1) * poly);
}
}
e.* = crc;
}
break :blk table;
};
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Polynomial
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crc: I,
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Crc32
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init()
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pub fn init() Self {
const initial = if (algorithm.reflect_input)
@bitReverse(@as(I, algorithm.initial)) >> (@bitSizeOf(I) - @bitSizeOf(W))
else
@as(I, algorithm.initial) << (@bitSizeOf(I) - @bitSizeOf(W));
return Self{ .crc = initial };
}
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init()
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inline fn tableEntry(index: I) I {
return lookup_table[@as(u8, @intCast(index & 0xFF))];
}
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update()
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pub fn update(self: *Self, bytes: []const u8) void {
var i: usize = 0;
if (@bitSizeOf(I) <= 8) {
while (i < bytes.len) : (i += 1) {
self.crc = tableEntry(self.crc ^ bytes[i]);
}
} else if (algorithm.reflect_input) {
while (i < bytes.len) : (i += 1) {
const table_index = self.crc ^ bytes[i];
self.crc = tableEntry(table_index) ^ (self.crc >> 8);
}
} else {
while (i < bytes.len) : (i += 1) {
const table_index = (self.crc >> (@bitSizeOf(I) - 8)) ^ bytes[i];
self.crc = tableEntry(table_index) ^ (self.crc << 8);
}
}
}
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final()
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pub fn final(self: Self) W {
var c = self.crc;
if (algorithm.reflect_input != algorithm.reflect_output) {
c = @bitReverse(c);
}
if (!algorithm.reflect_output) {
c >>= @bitSizeOf(I) - @bitSizeOf(W);
}
return @as(W, @intCast(c ^ algorithm.xor_output));
}
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hash()
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pub fn hash(bytes: []const u8) W {
var c = Self.init();
c.update(bytes);
return c.final();
}
};
}
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Test:crc32 ieee
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pub const Polynomial = enum(u32) {
IEEE = 0xedb88320,
Castagnoli = 0x82f63b78,
Koopman = 0xeb31d82e,
_,
};
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Test:crc32 castagnoli
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// IEEE is by far the most common CRC and so is aliased by default.
pub const Crc32 = Crc32WithPoly(.IEEE);
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Crc32SmallWithPoly()
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// slicing-by-8 crc32 implementation.
pub fn Crc32WithPoly(comptime poly: Polynomial) type {
return struct {
const Self = @This();
const lookup_tables = block: {
@setEvalBranchQuota(20000);
var tables: [8][256]u32 = undefined;
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init()
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for (&tables[0], 0..) |*e, i| {
var crc = @as(u32, @intCast(i));
var j: usize = 0;
while (j < 8) : (j += 1) {
if (crc & 1 == 1) {
crc = (crc >> 1) ^ @intFromEnum(poly);
} else {
crc = (crc >> 1);
}
}
e.* = crc;
}
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update()
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var i: usize = 0;
while (i < 256) : (i += 1) {
var crc = tables[0][i];
var j: usize = 1;
while (j < 8) : (j += 1) {
const index: u8 = @truncate(crc);
crc = tables[0][index] ^ (crc >> 8);
tables[j][i] = crc;
}
}
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final()
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break :block tables;
};
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hash()
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crc: u32,
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Test:small crc32 ieee
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pub fn init() Self {
return Self{ .crc = 0xffffffff };
}
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Test:small crc32 castagnoli
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pub fn update(self: *Self, input: []const u8) void {
var i: usize = 0;
while (i + 8 <= input.len) : (i += 8) {
const p = input[i..][0..8];
// Unrolling this way gives ~50Mb/s increase
self.crc ^= std.mem.readIntLittle(u32, p[0..4]);
self.crc =
lookup_tables[0][p[7]] ^
lookup_tables[1][p[6]] ^
lookup_tables[2][p[5]] ^
lookup_tables[3][p[4]] ^
lookup_tables[4][@as(u8, @truncate(self.crc >> 24))] ^
lookup_tables[5][@as(u8, @truncate(self.crc >> 16))] ^
lookup_tables[6][@as(u8, @truncate(self.crc >> 8))] ^
lookup_tables[7][@as(u8, @truncate(self.crc >> 0))];
}
while (i < input.len) : (i += 1) {
const index = @as(u8, @truncate(self.crc)) ^ input[i];
self.crc = (self.crc >> 8) ^ lookup_tables[0][index];
}
}
pub fn final(self: *Self) u32 {
return ~self.crc;
}
pub fn hash(input: []const u8) u32 {
var c = Self.init();
c.update(input);
return c.final();
}
};
}
test "crc32 ieee" {
const Crc32Ieee = Crc32WithPoly(.IEEE);
try testing.expect(Crc32Ieee.hash("") == 0x00000000);
try testing.expect(Crc32Ieee.hash("a") == 0xe8b7be43);
try testing.expect(Crc32Ieee.hash("abc") == 0x352441c2);
}
test "crc32 castagnoli" {
const Crc32Castagnoli = Crc32WithPoly(.Castagnoli);
try testing.expect(Crc32Castagnoli.hash("") == 0x00000000);
try testing.expect(Crc32Castagnoli.hash("a") == 0xc1d04330);
try testing.expect(Crc32Castagnoli.hash("abc") == 0x364b3fb7);
}
// half-byte lookup table implementation.
pub fn Crc32SmallWithPoly(comptime poly: Polynomial) type {
return struct {
const Self = @This();
const lookup_table = block: {
var table: [16]u32 = undefined;
for (&table, 0..) |*e, i| {
var crc = @as(u32, @intCast(i * 16));
var j: usize = 0;
while (j < 8) : (j += 1) {
if (crc & 1 == 1) {
crc = (crc >> 1) ^ @intFromEnum(poly);
} else {
crc = (crc >> 1);
}
}
e.* = crc;
}
break :block table;
};
crc: u32,
pub fn init() Self {
return Self{ .crc = 0xffffffff };
}
pub fn update(self: *Self, input: []const u8) void {
for (input) |b| {
self.crc = lookup_table[@as(u4, @truncate(self.crc ^ (b >> 0)))] ^ (self.crc >> 4);
self.crc = lookup_table[@as(u4, @truncate(self.crc ^ (b >> 4)))] ^ (self.crc >> 4);
}
}
pub fn final(self: *Self) u32 {
return ~self.crc;
}
pub fn hash(input: []const u8) u32 {
var c = Self.init();
c.update(input);
return c.final();
}
};
}
test "small crc32 ieee" {
const Crc32Ieee = Crc32SmallWithPoly(.IEEE);
try testing.expect(Crc32Ieee.hash("") == 0x00000000);
try testing.expect(Crc32Ieee.hash("a") == 0xe8b7be43);
try testing.expect(Crc32Ieee.hash("abc") == 0x352441c2);
}
test "small crc32 castagnoli" {
const Crc32Castagnoli = Crc32SmallWithPoly(.Castagnoli);
try testing.expect(Crc32Castagnoli.hash("") == 0x00000000);
try testing.expect(Crc32Castagnoli.hash("a") == 0xc1d04330);
try testing.expect(Crc32Castagnoli.hash("abc") == 0x364b3fb7);
}
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zig/lib/std /
hash/crc.zig