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std: fix bug in Pcg32 fill function (#13894)

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The PCG32 fill function seems to have been copy-pasted from code using u64, so requesting `n` bytes where `(n & 7) > 4` bytes would cause the last few bytes to be all 0.
This commit is contained in:
fsh 2022-12-12 20:19:49 +01:00 committed by Andrew Kelley
parent cdcb746cc2
commit 7d0d99aac0
1 changed files with 10 additions and 6 deletions
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16
lib/std/rand/Pcg.zig
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@ -51,7 +51,7 @@ fn seedTwo(self: *Pcg, init_s: u64, init_i: u64) void {
pub fn fill(self: *Pcg, buf: []u8) void { pub fn fill(self: *Pcg, buf: []u8) void {
var i: usize = 0; var i: usize = 0;
const aligned_len = buf.len - (buf.len & 7); const aligned_len = buf.len - (buf.len & 3);
// Complete 4 byte segments. // Complete 4 byte segments.
while (i < aligned_len) : (i += 4) { while (i < aligned_len) : (i += 4) {
@ -108,11 +108,15 @@ test "pcg fill" {
3247963454, 3247963454,
}; };
for (seq) |s| { var i: u32 = 0;
var buf0: [4]u8 = undefined; while (i < seq.len) : (i += 2) {
var buf1: [3]u8 = undefined; var buf0: [8]u8 = undefined;
std.mem.writeIntLittle(u32, &buf0, s); std.mem.writeIntLittle(u32, buf0[0..4], seq[i]);
std.mem.writeIntLittle(u32, buf0[4..8], seq[i + 1]);
var buf1: [7]u8 = undefined;
r.fill(&buf1); r.fill(&buf1);
try std.testing.expect(std.mem.eql(u8, buf0[0..3], buf1[0..]));
try std.testing.expect(std.mem.eql(u8, buf0[0..7], buf1[0..]));
} }
} }