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1/* Copyright 2010 Google Inc. All Rights Reserved.\r
2\r
3 Distributed under MIT license.\r
4 See file LICENSE for detail or copy at https://opensource.org/licenses/MIT\r
5*/\r
6\r
7/* Write bits into a byte array. */\r
8\r
9#ifndef BROTLI_ENC_WRITE_BITS_H_\r
10#define BROTLI_ENC_WRITE_BITS_H_\r
11\r
12#include <assert.h>\r
13#include <stdio.h> /* printf */\r
14\r
15#include "../common/types.h"\r
16#include "./port.h"\r
17\r
18#if defined(__cplusplus) || defined(c_plusplus)\r
19extern "C" {\r
20#endif\r
21\r
22/*#define BIT_WRITER_DEBUG */\r
23\r
24/* This function writes bits into bytes in increasing addresses, and within\r
25 a byte least-significant-bit first.\r
26\r
27 The function can write up to 56 bits in one go with WriteBits\r
28 Example: let's assume that 3 bits (Rs below) have been written already:\r
29\r
30 BYTE-0 BYTE+1 BYTE+2\r
31\r
32 0000 0RRR 0000 0000 0000 0000\r
33\r
34 Now, we could write 5 or less bits in MSB by just sifting by 3\r
35 and OR'ing to BYTE-0.\r
36\r
37 For n bits, we take the last 5 bits, OR that with high bits in BYTE-0,\r
38 and locate the rest in BYTE+1, BYTE+2, etc. */\r
39static BROTLI_INLINE void BrotliWriteBits(size_t n_bits,\r
40 uint64_t bits,\r
41 size_t * BROTLI_RESTRICT pos,\r
42 uint8_t * BROTLI_RESTRICT array) {\r
43#ifdef IS_LITTLE_ENDIAN\r
44 /* This branch of the code can write up to 56 bits at a time,\r
45 7 bits are lost by being perhaps already in *p and at least\r
46 1 bit is needed to initialize the bit-stream ahead (i.e. if 7\r
47 bits are in *p and we write 57 bits, then the next write will\r
48 access a byte that was never initialized). */\r
49 uint8_t *p = &array[*pos >> 3];\r
50 uint64_t v = *p;\r
51#ifdef BIT_WRITER_DEBUG\r
52 printf("WriteBits %2d 0x%016llx %10d\n", n_bits, bits, *pos);\r
53#endif\r
54 assert((bits >> n_bits) == 0);\r
55 assert(n_bits <= 56);\r
56 v |= bits << (*pos & 7);\r
57 BROTLI_UNALIGNED_STORE64(p, v); /* Set some bits. */\r
58 *pos += n_bits;\r
59#else\r
60 /* implicit & 0xff is assumed for uint8_t arithmetics */\r
61 uint8_t *array_pos = &array[*pos >> 3];\r
62 const size_t bits_reserved_in_first_byte = (*pos & 7);\r
63 size_t bits_left_to_write;\r
64 bits <<= bits_reserved_in_first_byte;\r
65 *array_pos++ |= (uint8_t)bits;\r
66 for (bits_left_to_write = n_bits + bits_reserved_in_first_byte;\r
67 bits_left_to_write >= 9;\r
68 bits_left_to_write -= 8) {\r
69 bits >>= 8;\r
70 *array_pos++ = (uint8_t)bits;\r
71 }\r
72 *array_pos = 0;\r
73 *pos += n_bits;\r
74#endif\r
75}\r
76\r
77static BROTLI_INLINE void BrotliWriteBitsPrepareStorage(\r
78 size_t pos, uint8_t *array) {\r
79#ifdef BIT_WRITER_DEBUG\r
80 printf("WriteBitsPrepareStorage %10d\n", pos);\r
81#endif\r
82 assert((pos & 7) == 0);\r
83 array[pos >> 3] = 0;\r
84}\r
85\r
86#if defined(__cplusplus) || defined(c_plusplus)\r
87} /* extern "C" */\r
88#endif\r
89\r
90#endif /* BROTLI_ENC_WRITE_BITS_H_ */\r