| /* 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) { |
| #ifdef 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_ */ |