gecko-dev/mfbt/HashFunctions.cpp
Iain Ireland 094d5b88a8 Bug 1719396: Don't hash sizeof(size_t) in HashBytes r=glandium
The loop in HashBytes currently hashes both a word of data (as intended) and the length of that word of data (a constant).

This was [acknowledged as a bug](https://bugzilla.mozilla.org/show_bug.cgi?id=729940#c49) when first written, but slipped through the cracks and was never fixed.

Differential Revision: https://phabricator.services.mozilla.com/D119466
2021-07-19 21:35:40 +00:00

38 lines
1.0 KiB
C++

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Implementations of hash functions. */
#include "mozilla/HashFunctions.h"
#include "mozilla/Types.h"
#include <string.h>
namespace mozilla {
uint32_t HashBytes(const void* aBytes, size_t aLength) {
uint32_t hash = 0;
const char* b = reinterpret_cast<const char*>(aBytes);
/* Walk word by word. */
size_t i = 0;
for (; i < aLength - (aLength % sizeof(size_t)); i += sizeof(size_t)) {
/* Do an explicitly unaligned load of the data. */
size_t data;
memcpy(&data, b + i, sizeof(size_t));
hash = AddToHash(hash, data);
}
/* Get the remaining bytes. */
for (; i < aLength; i++) {
hash = AddToHash(hash, b[i]);
}
return hash;
}
} /* namespace mozilla */