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/* -*- 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 */
#include "mozilla/Maybe.h"
#include "mozilla/TextUtils.h"
#include "mozilla/Types.h"
#include "mozilla/Utf8.h"
#include <stddef.h>
#include <stdint.h>
MFBT_API bool mozilla::detail::IsValidUtf8(const void* aCodeUnits,
size_t aCount) {
const auto* s = reinterpret_cast<const unsigned char*>(aCodeUnits);
const auto* const limit = s + aCount;
while (s < limit) {
unsigned char c = *s++;
// If the first byte is ASCII, it's the only one in the code point. Have a
// fast path that avoids all the rest of the work and looping in that case.
if (IsAscii(c)) {
Maybe<char32_t> maybeCodePoint =
DecodeOneUtf8CodePoint(Utf8Unit(c), &s, limit);
if (maybeCodePoint.isNothing()) {
return false;
MOZ_ASSERT(s == limit);
return true;