| // 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_ |