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https://github.com/google/brotli.git
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86 lines
2.2 KiB
C
86 lines
2.2 KiB
C
/* Copyright 2013 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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/* Heuristics for deciding about the UTF8-ness of strings. */
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#include "utf8_util.h"
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#include <brotli/types.h>
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#if defined(__cplusplus) || defined(c_plusplus)
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extern "C" {
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#endif
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static size_t BrotliParseAsUTF8(
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int* symbol, const uint8_t* input, size_t size) {
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/* ASCII */
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if ((input[0] & 0x80) == 0) {
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*symbol = input[0];
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if (*symbol > 0) {
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return 1;
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}
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}
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/* 2-byte UTF8 */
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if (size > 1u &&
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(input[0] & 0xE0) == 0xC0 &&
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(input[1] & 0xC0) == 0x80) {
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*symbol = (((input[0] & 0x1F) << 6) |
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(input[1] & 0x3F));
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if (*symbol > 0x7F) {
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return 2;
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}
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}
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/* 3-byte UFT8 */
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if (size > 2u &&
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(input[0] & 0xF0) == 0xE0 &&
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(input[1] & 0xC0) == 0x80 &&
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(input[2] & 0xC0) == 0x80) {
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*symbol = (((input[0] & 0x0F) << 12) |
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((input[1] & 0x3F) << 6) |
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(input[2] & 0x3F));
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if (*symbol > 0x7FF) {
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return 3;
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}
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}
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/* 4-byte UFT8 */
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if (size > 3u &&
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(input[0] & 0xF8) == 0xF0 &&
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(input[1] & 0xC0) == 0x80 &&
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(input[2] & 0xC0) == 0x80 &&
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(input[3] & 0xC0) == 0x80) {
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*symbol = (((input[0] & 0x07) << 18) |
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((input[1] & 0x3F) << 12) |
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((input[2] & 0x3F) << 6) |
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(input[3] & 0x3F));
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if (*symbol > 0xFFFF && *symbol <= 0x10FFFF) {
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return 4;
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}
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}
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/* Not UTF8, emit a special symbol above the UTF8-code space */
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*symbol = 0x110000 | input[0];
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return 1;
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}
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/* Returns 1 if at least min_fraction of the data is UTF8-encoded.*/
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BROTLI_BOOL BrotliIsMostlyUTF8(
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const uint8_t* data, const size_t pos, const size_t mask,
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const size_t length, const double min_fraction) {
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size_t size_utf8 = 0;
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size_t i = 0;
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while (i < length) {
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int symbol;
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size_t bytes_read =
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BrotliParseAsUTF8(&symbol, &data[(pos + i) & mask], length - i);
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i += bytes_read;
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if (symbol < 0x110000) size_utf8 += bytes_read;
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}
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return TO_BROTLI_BOOL((double)size_utf8 > min_fraction * (double)length);
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}
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#if defined(__cplusplus) || defined(c_plusplus)
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} /* extern "C" */
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#endif
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