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