1/* Copyright 2013 Google Inc. All Rights Reserved.
2
3 Distributed under MIT license.
4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
5*/
6
7/* Heuristics for deciding about the UTF8-ness of strings. */
8
9#include "./utf8_util.h"
10
11#include <brotli/types.h>
12
13#if defined(__cplusplus) || defined(c_plusplus)
14extern "C" {
15#endif
16
17static size_t BrotliParseAsUTF8(
18 int* symbol, const uint8_t* input, size_t size) {
19 /* ASCII */
20 if ((input[0] & 0x80) == 0) {
21 *symbol = input[0];
22 if (*symbol > 0) {
23 return 1;
24 }
25 }
26 /* 2-byte UTF8 */
27 if (size > 1u &&
28 (input[0] & 0xE0) == 0xC0 &&
29 (input[1] & 0xC0) == 0x80) {
30 *symbol = (((input[0] & 0x1F) << 6) |
31 (input[1] & 0x3F));
32 if (*symbol > 0x7F) {
33 return 2;
34 }
35 }
36 /* 3-byte UFT8 */
37 if (size > 2u &&
38 (input[0] & 0xF0) == 0xE0 &&
39 (input[1] & 0xC0) == 0x80 &&
40 (input[2] & 0xC0) == 0x80) {
41 *symbol = (((input[0] & 0x0F) << 12) |
42 ((input[1] & 0x3F) << 6) |
43 (input[2] & 0x3F));
44 if (*symbol > 0x7FF) {
45 return 3;
46 }
47 }
48 /* 4-byte UFT8 */
49 if (size > 3u &&
50 (input[0] & 0xF8) == 0xF0 &&
51 (input[1] & 0xC0) == 0x80 &&
52 (input[2] & 0xC0) == 0x80 &&
53 (input[3] & 0xC0) == 0x80) {
54 *symbol = (((input[0] & 0x07) << 18) |
55 ((input[1] & 0x3F) << 12) |
56 ((input[2] & 0x3F) << 6) |
57 (input[3] & 0x3F));
58 if (*symbol > 0xFFFF && *symbol <= 0x10FFFF) {
59 return 4;
60 }
61 }
62 /* Not UTF8, emit a special symbol above the UTF8-code space */
63 *symbol = 0x110000 | input[0];
64 return 1;
65}
66
67/* Returns 1 if at least min_fraction of the data is UTF8-encoded.*/
68BROTLI_BOOL BrotliIsMostlyUTF8(
69 const uint8_t* data, const size_t pos, const size_t mask,
70 const size_t length, const double min_fraction) {
71 size_t size_utf8 = 0;
72 size_t i = 0;
73 while (i < length) {
74 int symbol;
75 size_t bytes_read =
76 BrotliParseAsUTF8(&symbol, &data[(pos + i) & mask], length - i);
77 i += bytes_read;
78 if (symbol < 0x110000) size_utf8 += bytes_read;
79 }
80 return TO_BROTLI_BOOL(size_utf8 > min_fraction * (double)length);
81}
82
83#if defined(__cplusplus) || defined(c_plusplus)
84} /* extern "C" */
85#endif
86