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Diffstat (limited to 'modules/brotli/enc/ringbuffer.h')
| -rw-r--r-- | modules/brotli/enc/ringbuffer.h | 164 |
1 files changed, 164 insertions, 0 deletions
diff --git a/modules/brotli/enc/ringbuffer.h b/modules/brotli/enc/ringbuffer.h new file mode 100644 index 000000000..86079a89d --- /dev/null +++ b/modules/brotli/enc/ringbuffer.h @@ -0,0 +1,164 @@ +/* Copyright 2013 Google Inc. All Rights Reserved. + + Distributed under MIT license. + See file LICENSE for detail or copy at https://opensource.org/licenses/MIT +*/ + +/* Sliding window over the input data. */ + +#ifndef BROTLI_ENC_RINGBUFFER_H_ +#define BROTLI_ENC_RINGBUFFER_H_ + +#include <string.h> /* memcpy */ + +#include "../common/platform.h" +#include <brotli/types.h> +#include "./memory.h" +#include "./quality.h" + +#if defined(__cplusplus) || defined(c_plusplus) +extern "C" { +#endif + +/* A RingBuffer(window_bits, tail_bits) contains `1 << window_bits' bytes of + data in a circular manner: writing a byte writes it to: + `position() % (1 << window_bits)'. + For convenience, the RingBuffer array contains another copy of the + first `1 << tail_bits' bytes: + buffer_[i] == buffer_[i + (1 << window_bits)], if i < (1 << tail_bits), + and another copy of the last two bytes: + buffer_[-1] == buffer_[(1 << window_bits) - 1] and + buffer_[-2] == buffer_[(1 << window_bits) - 2]. */ +typedef struct RingBuffer { + /* Size of the ring-buffer is (1 << window_bits) + tail_size_. */ + const uint32_t size_; + const uint32_t mask_; + const uint32_t tail_size_; + const uint32_t total_size_; + + uint32_t cur_size_; + /* Position to write in the ring buffer. */ + uint32_t pos_; + /* The actual ring buffer containing the copy of the last two bytes, the data, + and the copy of the beginning as a tail. */ + uint8_t* data_; + /* The start of the ring-buffer. */ + uint8_t* buffer_; +} RingBuffer; + +static BROTLI_INLINE void RingBufferInit(RingBuffer* rb) { + rb->cur_size_ = 0; + rb->pos_ = 0; + rb->data_ = 0; + rb->buffer_ = 0; +} + +static BROTLI_INLINE void RingBufferSetup( + const BrotliEncoderParams* params, RingBuffer* rb) { + int window_bits = ComputeRbBits(params); + int tail_bits = params->lgblock; + *(uint32_t*)&rb->size_ = 1u << window_bits; + *(uint32_t*)&rb->mask_ = (1u << window_bits) - 1; + *(uint32_t*)&rb->tail_size_ = 1u << tail_bits; + *(uint32_t*)&rb->total_size_ = rb->size_ + rb->tail_size_; +} + +static BROTLI_INLINE void RingBufferFree(MemoryManager* m, RingBuffer* rb) { + BROTLI_FREE(m, rb->data_); +} + +/* Allocates or re-allocates data_ to the given length + plus some slack + region before and after. Fills the slack regions with zeros. */ +static BROTLI_INLINE void RingBufferInitBuffer( + MemoryManager* m, const uint32_t buflen, RingBuffer* rb) { + static const size_t kSlackForEightByteHashingEverywhere = 7; + uint8_t* new_data = BROTLI_ALLOC( + m, uint8_t, 2 + buflen + kSlackForEightByteHashingEverywhere); + size_t i; + if (BROTLI_IS_OOM(m)) return; + if (rb->data_) { + memcpy(new_data, rb->data_, + 2 + rb->cur_size_ + kSlackForEightByteHashingEverywhere); + BROTLI_FREE(m, rb->data_); + } + rb->data_ = new_data; + rb->cur_size_ = buflen; + rb->buffer_ = rb->data_ + 2; + rb->buffer_[-2] = rb->buffer_[-1] = 0; + for (i = 0; i < kSlackForEightByteHashingEverywhere; ++i) { + rb->buffer_[rb->cur_size_ + i] = 0; + } +} + +static BROTLI_INLINE void RingBufferWriteTail( + const uint8_t* bytes, size_t n, RingBuffer* rb) { + const size_t masked_pos = rb->pos_ & rb->mask_; + if (BROTLI_PREDICT_FALSE(masked_pos < rb->tail_size_)) { + /* Just fill the tail buffer with the beginning data. */ + const size_t p = rb->size_ + masked_pos; + memcpy(&rb->buffer_[p], bytes, + BROTLI_MIN(size_t, n, rb->tail_size_ - masked_pos)); + } +} + +/* Push bytes into the ring buffer. */ +static BROTLI_INLINE void RingBufferWrite( + MemoryManager* m, const uint8_t* bytes, size_t n, RingBuffer* rb) { + if (rb->pos_ == 0 && n < rb->tail_size_) { + /* Special case for the first write: to process the first block, we don't + need to allocate the whole ring-buffer and we don't need the tail + either. However, we do this memory usage optimization only if the + first write is less than the tail size, which is also the input block + size, otherwise it is likely that other blocks will follow and we + will need to reallocate to the full size anyway. */ + rb->pos_ = (uint32_t)n; + RingBufferInitBuffer(m, rb->pos_, rb); + if (BROTLI_IS_OOM(m)) return; + memcpy(rb->buffer_, bytes, n); + return; + } + if (rb->cur_size_ < rb->total_size_) { + /* Lazily allocate the full buffer. */ + RingBufferInitBuffer(m, rb->total_size_, rb); + if (BROTLI_IS_OOM(m)) return; + /* Initialize the last two bytes to zero, so that we don't have to worry + later when we copy the last two bytes to the first two positions. */ + rb->buffer_[rb->size_ - 2] = 0; + rb->buffer_[rb->size_ - 1] = 0; + } + { + const size_t masked_pos = rb->pos_ & rb->mask_; + /* The length of the writes is limited so that we do not need to worry + about a write */ + RingBufferWriteTail(bytes, n, rb); + if (BROTLI_PREDICT_TRUE(masked_pos + n <= rb->size_)) { + /* A single write fits. */ + memcpy(&rb->buffer_[masked_pos], bytes, n); + } else { + /* Split into two writes. + Copy into the end of the buffer, including the tail buffer. */ + memcpy(&rb->buffer_[masked_pos], bytes, + BROTLI_MIN(size_t, n, rb->total_size_ - masked_pos)); + /* Copy into the beginning of the buffer */ + memcpy(&rb->buffer_[0], bytes + (rb->size_ - masked_pos), + n - (rb->size_ - masked_pos)); + } + } + { + BROTLI_BOOL not_first_lap = (rb->pos_ & (1u << 31)) != 0; + uint32_t rb_pos_mask = (1u << 31) - 1; + rb->buffer_[-2] = rb->buffer_[rb->size_ - 2]; + rb->buffer_[-1] = rb->buffer_[rb->size_ - 1]; + rb->pos_ = (rb->pos_ & rb_pos_mask) + (uint32_t)(n & rb_pos_mask); + if (not_first_lap) { + /* Wrap, but preserve not-a-first-lap feature. */ + rb->pos_ |= 1u << 31; + } + } +} + +#if defined(__cplusplus) || defined(c_plusplus) +} /* extern "C" */ +#endif + +#endif /* BROTLI_ENC_RINGBUFFER_H_ */ |