skia / external / github.com / google / brotli / 5805f99a533a8f8118699c0100d8c102f3605f65 / . / c / enc / write_bits.h

/* 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 "../common/platform.h" | |

#include <brotli/types.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) { | |

#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. */ | |

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); | |

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_ */ |