1//! https://tools.ietf.org/html/rfc1950#section-9
2//! https://github.com/madler/zlib/blob/master/adler32.c
3
4const Adler32 = @This();
5const std = @import("std");
6const testing = std.testing;
7
8adler: u32 = 1,
9
10pub fn permute(state: u32, input: []const u8) u32 {
11 const base = 65521;
12 const nmax = 5552;
13
14 var s1 = state & 0xffff;
15 var s2 = (state >> 16) & 0xffff;
16
17 if (input.len == 1) {
18 s1 +%= input[0];
19 if (s1 >= base) {
20 s1 -= base;
21 }
22 s2 +%= s1;
23 if (s2 >= base) {
24 s2 -= base;
25 }
26 } else if (input.len < 16) {
27 for (input) |b| {
28 s1 +%= b;
29 s2 +%= s1;
30 }
31 if (s1 >= base) {
32 s1 -= base;
33 }
34
35 s2 %= base;
36 } else {
37 const n = nmax / 16; // note: 16 | nmax
38
39 var i: usize = 0;
40
41 while (i + nmax <= input.len) {
42 var rounds: usize = 0;
43 while (rounds < n) : (rounds += 1) {
44 comptime var j: usize = 0;
45 inline while (j < 16) : (j += 1) {
46 s1 +%= input[i + j];
47 s2 +%= s1;
48 }
49 i += 16;
50 }
51
52 s1 %= base;
53 s2 %= base;
54 }
55
56 if (i < input.len) {
57 while (i + 16 <= input.len) : (i += 16) {
58 comptime var j: usize = 0;
59 inline while (j < 16) : (j += 1) {
60 s1 +%= input[i + j];
61 s2 +%= s1;
62 }
63 }
64 while (i < input.len) : (i += 1) {
65 s1 +%= input[i];
66 s2 +%= s1;
67 }
68
69 s1 %= base;
70 s2 %= base;
71 }
72 }
73
74 return s1 | (s2 << 16);
75}
76
77pub fn update(a: *Adler32, input: []const u8) void {
78 a.adler = permute(a.adler, input);
79}
80
81pub fn hash(input: []const u8) u32 {
82 return permute(1, input);
83}
84
85test "sanity" {
86 try testing.expectEqual(@as(u32, 0x620062), hash("a"));
87 try testing.expectEqual(@as(u32, 0xbc002ed), hash("example"));
88}
89
90test "long" {
91 const long1: [1024]u8 = @splat(1);
92 try testing.expectEqual(@as(u32, 0x06780401), hash(long1[0..]));
93
94 const long2: [1025]u8 = @splat(1);
95 try testing.expectEqual(@as(u32, 0x0a7a0402), hash(long2[0..]));
96}
97
98test "very long" {
99 const long: [5553]u8 = @splat(1);
100 try testing.expectEqual(@as(u32, 0x707f15b2), hash(long[0..]));
101}
102
103test "very long with variation" {
104 const long = comptime blk: {
105 @setEvalBranchQuota(7000);
106 var result: [6000]u8 = undefined;
107
108 var i: usize = 0;
109 while (i < result.len) : (i += 1) {
110 result[i] = @as(u8, @truncate(i));
111 }
112
113 break :blk result;
114 };
115
116 try testing.expectEqual(@as(u32, 0x5af38d6e), hash(long[0..]));
117}