zig/std/hash/adler.zig

108 lines
2.8 KiB
Zig

// Adler32 checksum.
//
// https://tools.ietf.org/html/rfc1950#section-9
// https://github.com/madler/zlib/blob/master/adler32.c
const std = @import("../index.zig");
const debug = std.debug;
pub const Adler32 = struct {
const base = 65521;
const nmax = 5552;
adler: u32,
pub fn init() Adler32 {
return Adler32{ .adler = 1 };
}
// This fast variant is taken from zlib. It reduces the required modulos and unrolls longer
// buffer inputs and should be much quicker.
pub fn update(self: *Adler32, input: []const u8) void {
var s1 = self.adler & 0xffff;
var s2 = (self.adler >> 16) & 0xffff;
if (input.len == 1) {
s1 +%= input[0];
if (s1 >= base) {
s1 -= base;
}
s2 +%= s1;
if (s2 >= base) {
s2 -= base;
}
} else if (input.len < 16) {
for (input) |b| {
s1 +%= b;
s2 +%= s1;
}
if (s1 >= base) {
s1 -= base;
}
s2 %= base;
} else {
var i: usize = 0;
while (i + nmax <= input.len) : (i += nmax) {
const n = nmax / 16; // note: 16 | nmax
var rounds: usize = 0;
while (rounds < n) : (rounds += 1) {
comptime var j: usize = 0;
inline while (j < 16) : (j += 1) {
s1 +%= input[i + n * j];
s2 +%= s1;
}
}
}
if (i < input.len) {
while (i + 16 <= input.len) : (i += 16) {
comptime var j: usize = 0;
inline while (j < 16) : (j += 1) {
s1 +%= input[i + j];
s2 +%= s1;
}
}
while (i < input.len) : (i += 1) {
s1 +%= input[i];
s2 +%= s1;
}
s1 %= base;
s2 %= base;
}
}
self.adler = s1 | (s2 << 16);
}
pub fn final(self: *Adler32) u32 {
return self.adler;
}
pub fn hash(input: []const u8) u32 {
var c = Adler32.init();
c.update(input);
return c.final();
}
};
test "adler32 sanity" {
debug.assert(Adler32.hash("a") == 0x620062);
debug.assert(Adler32.hash("example") == 0xbc002ed);
}
test "adler32 long" {
const long1 = []u8{1} ** 1024;
debug.assert(Adler32.hash(long1[0..]) == 0x06780401);
const long2 = []u8{1} ** 1025;
debug.assert(Adler32.hash(long2[0..]) == 0x0a7a0402);
}
test "adler32 very long" {
const long = []u8{1} ** 5553;
debug.assert(Adler32.hash(long[0..]) == 0x707f15b2);
}