/* Copyright 2010 Google Inc. All Rights Reserved. | |
Distributed under MIT license. | |
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT | |
*/ | |
/* Write bits into a byte array. */ | |
#ifndef BROTLI_ENC_WRITE_BITS_H_ | |
#define BROTLI_ENC_WRITE_BITS_H_ | |
#include <assert.h> | |
#include <stdio.h> /* printf */ | |
#include "../common/types.h" | |
#include "./port.h" | |
#if defined(__cplusplus) || defined(c_plusplus) | |
extern "C" { | |
#endif | |
/*#define BIT_WRITER_DEBUG */ | |
/* This function writes bits into bytes in increasing addresses, and within | |
a byte least-significant-bit first. | |
The function can write up to 56 bits in one go with WriteBits | |
Example: let's assume that 3 bits (Rs below) have been written already: | |
BYTE-0 BYTE+1 BYTE+2 | |
0000 0RRR 0000 0000 0000 0000 | |
Now, we could write 5 or less bits in MSB by just sifting by 3 | |
and OR'ing to BYTE-0. | |
For n bits, we take the last 5 bits, OR that with high bits in BYTE-0, | |
and locate the rest in BYTE+1, BYTE+2, etc. */ | |
static BROTLI_INLINE void BrotliWriteBits(size_t n_bits, | |
uint64_t bits, | |
size_t * BROTLI_RESTRICT pos, | |
uint8_t * BROTLI_RESTRICT array) { | |
#ifdef IS_LITTLE_ENDIAN | |
/* This branch of the code can write up to 56 bits at a time, | |
7 bits are lost by being perhaps already in *p and at least | |
1 bit is needed to initialize the bit-stream ahead (i.e. if 7 | |
bits are in *p and we write 57 bits, then the next write will | |
access a byte that was never initialized). */ | |
uint8_t *p = &array[*pos >> 3]; | |
uint64_t v = *p; | |
#ifdef BIT_WRITER_DEBUG | |
printf("WriteBits %2d 0x%016llx %10d\n", n_bits, bits, *pos); | |
#endif | |
assert((bits >> n_bits) == 0); | |
assert(n_bits <= 56); | |
v |= bits << (*pos & 7); | |
BROTLI_UNALIGNED_STORE64(p, v); /* Set some bits. */ | |
*pos += n_bits; | |
#else | |
/* implicit & 0xff is assumed for uint8_t arithmetics */ | |
uint8_t *array_pos = &array[*pos >> 3]; | |
const size_t bits_reserved_in_first_byte = (*pos & 7); | |
size_t bits_left_to_write; | |
bits <<= bits_reserved_in_first_byte; | |
*array_pos++ |= (uint8_t)bits; | |
for (bits_left_to_write = n_bits + bits_reserved_in_first_byte; | |
bits_left_to_write >= 9; | |
bits_left_to_write -= 8) { | |
bits >>= 8; | |
*array_pos++ = (uint8_t)bits; | |
} | |
*array_pos = 0; | |
*pos += n_bits; | |
#endif | |
} | |
static BROTLI_INLINE void BrotliWriteBitsPrepareStorage( | |
size_t pos, uint8_t *array) { | |
#ifdef BIT_WRITER_DEBUG | |
printf("WriteBitsPrepareStorage %10d\n", pos); | |
#endif | |
assert((pos & 7) == 0); | |
array[pos >> 3] = 0; | |
} | |
#if defined(__cplusplus) || defined(c_plusplus) | |
} /* extern "C" */ | |
#endif | |
#endif /* BROTLI_ENC_WRITE_BITS_H_ */ |