/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
// Heuristics for deciding about the UTF8-ness of strings.
#include "./utf8_util.h"
#include "./types.h"
namespace brotli {
namespace {
size_t ParseAsUTF8(int* symbol, const uint8_t* input, size_t size) {
// ASCII
if ((input[0] & 0x80) == 0) {
*symbol = input[0];
if (*symbol > 0) {
return 1;
}
}
// 2-byte UTF8
if (size > 1u &&
(input[0] & 0xe0) == 0xc0 &&
(input[1] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x1f) << 6) |
(input[1] & 0x3f));
if (*symbol > 0x7f) {
return 2;
}
}
// 3-byte UFT8
if (size > 2u &&
(input[0] & 0xf0) == 0xe0 &&
(input[1] & 0xc0) == 0x80 &&
(input[2] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x0f) << 12) |
((input[1] & 0x3f) << 6) |
(input[2] & 0x3f));
if (*symbol > 0x7ff) {
return 3;
}
}
// 4-byte UFT8
if (size > 3u &&
(input[0] & 0xf8) == 0xf0 &&
(input[1] & 0xc0) == 0x80 &&
(input[2] & 0xc0) == 0x80 &&
(input[3] & 0xc0) == 0x80) {
*symbol = (((input[0] & 0x07) << 18) |
((input[1] & 0x3f) << 12) |
((input[2] & 0x3f) << 6) |
(input[3] & 0x3f));
if (*symbol > 0xffff && *symbol <= 0x10ffff) {
return 4;
}
}
// Not UTF8, emit a special symbol above the UTF8-code space
*symbol = 0x110000 | input[0];
return 1;
}
} // namespace
// Returns true if at least min_fraction of the data is UTF8-encoded.
bool IsMostlyUTF8(const uint8_t* data, const size_t pos, const size_t mask,
const size_t length, const double min_fraction) {
size_t size_utf8 = 0;
size_t i = 0;
while (i < length) {
int symbol;
size_t bytes_read = ParseAsUTF8(
&symbol, &data[(pos + i) & mask], length - i);
i += bytes_read;
if (symbol < 0x110000) size_utf8 += bytes_read;
}
return size_utf8 > min_fraction * static_cast<double>(length);
}
} // namespace brotli
