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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.
const std = @import("../index.zig");
const debug = std.debug;
pub const Polynomial = struct {
const IEEE = 0xedb88320;
const Castagnoli = 0x82f63b78;
const Koopman = 0xeb31d82e;
};
// IEEE is by far the most common CRC and so is aliased by default.
pub const Crc32 = Crc32WithPoly(Polynomial.IEEE);
// slicing-by-8 crc32 implementation.
pub fn Crc32WithPoly(comptime poly: u32) type {
return struct {
const Self = this;
const lookup_tables = comptime block: {
@setEvalBranchQuota(20000);
var tables: [8][256]u32 = undefined;
for (tables[0]) |*e, i| {
var crc = u32(i);
var j: usize = 0; while (j < 8) : (j += 1) {
if (crc & 1 == 1) {
crc = (crc >> 1) ^ poly;
} else {
crc = (crc >> 1);
}
}
*e = crc;
}
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 = @truncate(u8, crc);
crc = tables[0][index] ^ (crc >> 8);
tables[j][i] = crc;
}
}
break :block tables;
};
crc: u32,
pub fn init() Self {
return Self {
.crc = 0xffffffff,
};
}
pub fn update(self: &Self, input: []const u8) void {
var i: usize = 0;
while (i + 8 <= input.len) : (i += 8) {
const p = input[i..i+8];
// Unrolling this way gives ~50Mb/s increase
self.crc ^= (u32(p[0]) << 0);
self.crc ^= (u32(p[1]) << 8);
self.crc ^= (u32(p[2]) << 16);
self.crc ^= (u32(p[3]) << 24);
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][@truncate(u8, self.crc >> 24)] ^
lookup_tables[5][@truncate(u8, self.crc >> 16)] ^
lookup_tables[6][@truncate(u8, self.crc >> 8)] ^
lookup_tables[7][@truncate(u8, self.crc >> 0)];
}
while (i < input.len) : (i += 1) {
const index = @truncate(u8, 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(Polynomial.IEEE);
debug.assert(Crc32Ieee.hash("") == 0x00000000);
debug.assert(Crc32Ieee.hash("a") == 0xe8b7be43);
debug.assert(Crc32Ieee.hash("abc") == 0x352441c2);
}
test "crc32 castagnoli" {
const Crc32Castagnoli = Crc32WithPoly(Polynomial.Castagnoli);
debug.assert(Crc32Castagnoli.hash("") == 0x00000000);
debug.assert(Crc32Castagnoli.hash("a") == 0xc1d04330);
debug.assert(Crc32Castagnoli.hash("abc") == 0x364b3fb7);
}
// half-byte lookup table implementation.
pub fn Crc32SmallWithPoly(comptime poly: u32) type {
return struct {
const Self = this;
const lookup_table = comptime block: {
var table: [16]u32 = undefined;
for (table) |*e, i| {
var crc = u32(i * 16);
var j: usize = 0; while (j < 8) : (j += 1) {
if (crc & 1 == 1) {
crc = (crc >> 1) ^ 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[@truncate(u4, self.crc ^ (b >> 0))] ^ (self.crc >> 4);
self.crc = lookup_table[@truncate(u4, 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(Polynomial.IEEE);
debug.assert(Crc32Ieee.hash("") == 0x00000000);
debug.assert(Crc32Ieee.hash("a") == 0xe8b7be43);
debug.assert(Crc32Ieee.hash("abc") == 0x352441c2);
}
test "small crc32 castagnoli" {
const Crc32Castagnoli = Crc32SmallWithPoly(Polynomial.Castagnoli);
debug.assert(Crc32Castagnoli.hash("") == 0x00000000);
debug.assert(Crc32Castagnoli.hash("a") == 0xc1d04330);
debug.assert(Crc32Castagnoli.hash("abc") == 0x364b3fb7);
}
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