mirror of
https://github.com/google/brotli.git
synced 2024-11-26 13:20:06 +00:00
f0b88cbcdb
Changes suggested by @r-lyeh and @anthrotype. - Use a portable simple PRNG instead of rand_r() - add missing <assert.h> include - disambiguate log2() argument type - remove endian.h include from write_bits.h
92 lines
2.8 KiB
C++
92 lines
2.8 KiB
C++
// Copyright 2010 Google Inc. All Rights Reserved.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 (the "License");
|
|
// you may not use this file except in compliance with the License.
|
|
// You may obtain a copy of the License at
|
|
//
|
|
// http://www.apache.org/licenses/LICENSE-2.0
|
|
//
|
|
// Unless required by applicable law or agreed to in writing, software
|
|
// distributed under the License is distributed on an "AS IS" BASIS,
|
|
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
// See the License for the specific language governing permissions and
|
|
// limitations under the License.
|
|
//
|
|
// Write bits into a byte array.
|
|
|
|
#ifndef BROTLI_ENC_WRITE_BITS_H_
|
|
#define BROTLI_ENC_WRITE_BITS_H_
|
|
|
|
#include <assert.h>
|
|
#include <stdint.h>
|
|
#include <stdio.h>
|
|
|
|
#include "./port.h"
|
|
|
|
namespace brotli {
|
|
|
|
//#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.
|
|
inline void WriteBits(int n_bits,
|
|
uint64_t bits,
|
|
int * __restrict pos,
|
|
uint8_t * __restrict array) {
|
|
#ifdef BIT_WRITER_DEBUG
|
|
printf("WriteBits %2d 0x%016llx %10d\n", n_bits, bits, *pos);
|
|
#endif
|
|
assert(bits < 1ULL << n_bits);
|
|
#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;
|
|
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 int bits_reserved_in_first_byte = (*pos & 7);
|
|
bits <<= bits_reserved_in_first_byte;
|
|
*array_pos++ |= bits;
|
|
for (int bits_left_to_write = n_bits - 8 + bits_reserved_in_first_byte;
|
|
bits_left_to_write >= 1;
|
|
bits_left_to_write -= 8) {
|
|
bits >>= 8;
|
|
*array_pos++ = bits;
|
|
}
|
|
*array_pos = 0;
|
|
*pos += n_bits;
|
|
#endif
|
|
}
|
|
|
|
inline void WriteBitsPrepareStorage(int pos, uint8_t *array) {
|
|
#ifdef BIT_WRITER_DEBUG
|
|
printf("WriteBitsPrepareStorage %10d\n", pos);
|
|
#endif
|
|
assert((pos & 7) == 0);
|
|
array[pos >> 3] = 0;
|
|
}
|
|
|
|
} // namespace brotli
|
|
|
|
#endif // BROTLI_ENC_WRITE_BITS_H_
|