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// SPDX-License-Identifier: MIT
// Copyright (c) 2015-2021 Zig Contributors
// This file is part of [zig](https://ziglang.org/), which is MIT licensed.
// The MIT license requires this copyright notice to be included in all copies
// and substantial portions of the software.
// Adler32 checksum.
//
// https://tools.ietf.org/html/rfc1950#section-9
// https://github.com/madler/zlib/blob/master/adler32.c
const std = @import("../std.zig");
const testing = std.testing;
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 {
const n = nmax / 16; // note: 16 | nmax
var i: usize = 0;
while (i + nmax <= input.len) {
var rounds: usize = 0;
while (rounds < n) : (rounds += 1) {
comptime var j: usize = 0;
inline while (j < 16) : (j += 1) {
s1 +%= input[i + j];
s2 +%= s1;
}
i += 16;
}
s1 %= base;
s2 %= base;
}
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" {
testing.expectEqual(@as(u32, 0x620062), Adler32.hash("a"));
testing.expectEqual(@as(u32, 0xbc002ed), Adler32.hash("example"));
}
test "adler32 long" {
const long1 = [_]u8{1} ** 1024;
testing.expectEqual(@as(u32, 0x06780401), Adler32.hash(long1[0..]));
const long2 = [_]u8{1} ** 1025;
testing.expectEqual(@as(u32, 0x0a7a0402), Adler32.hash(long2[0..]));
}
test "adler32 very long" {
const long = [_]u8{1} ** 5553;
testing.expectEqual(@as(u32, 0x707f15b2), Adler32.hash(long[0..]));
}
test "adler32 very long with variation" {
const long = comptime blk: {
@setEvalBranchQuota(7000);
var result: [6000]u8 = undefined;
var i: usize = 0;
while (i < result.len) : (i += 1) {
result[i] = @truncate(u8, i);
}
break :blk result;
};
testing.expectEqual(@as(u32, 0x5af38d6e), std.hash.Adler32.hash(long[0..]));
}
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