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/* 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 <brotli/types.h>
#include "../common/platform.h"
#if defined(__cplusplus) || defined(c_plusplus)
extern "C" {
#endif
/* 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 shifting 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) {
BROTLI_LOG(("WriteBits %2d 0x%08x%08x %10d\n", (int)n_bits,
(uint32_t)(bits >> 32), (uint32_t)(bits & 0xFFFFFFFF),
(int)*pos));
BROTLI_DCHECK((bits >> n_bits) == 0);
BROTLI_DCHECK(n_bits <= 56);
#if defined(BROTLI_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 = (uint64_t)(*p); /* Zero-extend 8 to 64 bits. */
v |= bits << (*pos & 7);
BROTLI_UNALIGNED_STORE64LE(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) {
BROTLI_LOG(("WriteBitsPrepareStorage %10d\n", (int)pos));
BROTLI_DCHECK((pos & 7) == 0);
array[pos >> 3] = 0;
}
#if defined(__cplusplus) || defined(c_plusplus)
} /* extern "C" */
#endif
#endif /* BROTLI_ENC_WRITE_BITS_H_ */
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