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 /* Functions for encoding of integers into prefix codes the amount of extra
8 bits, and the actual values of the extra bits. */
9
10 #ifndef BROTLI_ENC_PREFIX_H_
11 #define BROTLI_ENC_PREFIX_H_
12
13 #include "../common/constants.h"
14 #include <brotli/port.h>
15 #include <brotli/types.h>
16 #include "./fast_log.h"
17
18 #if defined(__cplusplus) || defined(c_plusplus)
19 extern "C" {
20 #endif
21
22 /* Here distance_code is an intermediate code, i.e. one of the special codes or
23 the actual distance increased by BROTLI_NUM_DISTANCE_SHORT_CODES - 1. */
PrefixEncodeCopyDistance(size_t distance_code,size_t num_direct_codes,size_t postfix_bits,uint16_t * code,uint32_t * extra_bits)24 static BROTLI_INLINE void PrefixEncodeCopyDistance(size_t distance_code,
25 size_t num_direct_codes,
26 size_t postfix_bits,
27 uint16_t* code,
28 uint32_t* extra_bits) {
29 if (distance_code < BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes) {
30 *code = (uint16_t)distance_code;
31 *extra_bits = 0;
32 return;
33 } else {
34 size_t dist = ((size_t)1 << (postfix_bits + 2u)) +
35 (distance_code - BROTLI_NUM_DISTANCE_SHORT_CODES - num_direct_codes);
36 size_t bucket = Log2FloorNonZero(dist) - 1;
37 size_t postfix_mask = (1u << postfix_bits) - 1;
38 size_t postfix = dist & postfix_mask;
39 size_t prefix = (dist >> bucket) & 1;
40 size_t offset = (2 + prefix) << bucket;
41 size_t nbits = bucket - postfix_bits;
42 *code = (uint16_t)(
43 (BROTLI_NUM_DISTANCE_SHORT_CODES + num_direct_codes +
44 ((2 * (nbits - 1) + prefix) << postfix_bits) + postfix));
45 *extra_bits = (uint32_t)(
46 (nbits << 24) | ((dist - offset) >> postfix_bits));
47 }
48 }
49
50 #if defined(__cplusplus) || defined(c_plusplus)
51 } /* extern "C" */
52 #endif
53
54 #endif /* BROTLI_ENC_PREFIX_H_ */
55