/* 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 #include /* printf */ #include "../common/types.h" #include "./port.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 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; #ifdef BIT_WRITER_DEBUG printf("WriteBits %2d 0x%016llx %10d\n", n_bits, bits, *pos); #endif assert((bits >> n_bits) == 0); assert(n_bits <= 56); 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 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) { #ifdef BIT_WRITER_DEBUG printf("WriteBitsPrepareStorage %10d\n", pos); #endif assert((pos & 7) == 0); array[pos >> 3] = 0; } #if defined(__cplusplus) || defined(c_plusplus) } /* extern "C" */ #endif #endif /* BROTLI_ENC_WRITE_BITS_H_ */