135 lines
4.4 KiB
Go
135 lines
4.4 KiB
Go
package brotli
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/* Copyright 2013 Google Inc. All Rights Reserved.
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Distributed under MIT license.
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See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
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*/
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/* A ringBuffer(window_bits, tail_bits) contains `1 << window_bits' bytes of
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data in a circular manner: writing a byte writes it to:
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`position() % (1 << window_bits)'.
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For convenience, the ringBuffer array contains another copy of the
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first `1 << tail_bits' bytes:
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buffer_[i] == buffer_[i + (1 << window_bits)], if i < (1 << tail_bits),
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and another copy of the last two bytes:
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buffer_[-1] == buffer_[(1 << window_bits) - 1] and
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buffer_[-2] == buffer_[(1 << window_bits) - 2]. */
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type ringBuffer struct {
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size_ uint32
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mask_ uint32
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tail_size_ uint32
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total_size_ uint32
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cur_size_ uint32
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pos_ uint32
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data_ []byte
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buffer_ []byte
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}
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func ringBufferInit(rb *ringBuffer) {
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rb.pos_ = 0
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}
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func ringBufferSetup(params *encoderParams, rb *ringBuffer) {
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var window_bits int = computeRbBits(params)
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var tail_bits int = params.lgblock
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*(*uint32)(&rb.size_) = 1 << uint(window_bits)
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*(*uint32)(&rb.mask_) = (1 << uint(window_bits)) - 1
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*(*uint32)(&rb.tail_size_) = 1 << uint(tail_bits)
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*(*uint32)(&rb.total_size_) = rb.size_ + rb.tail_size_
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}
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const kSlackForEightByteHashingEverywhere uint = 7
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/* Allocates or re-allocates data_ to the given length + plus some slack
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region before and after. Fills the slack regions with zeros. */
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func ringBufferInitBuffer(buflen uint32, rb *ringBuffer) {
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var new_data []byte
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var i uint
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size := 2 + int(buflen) + int(kSlackForEightByteHashingEverywhere)
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if cap(rb.data_) < size {
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new_data = make([]byte, size)
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} else {
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new_data = rb.data_[:size]
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}
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if rb.data_ != nil {
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copy(new_data, rb.data_[:2+rb.cur_size_+uint32(kSlackForEightByteHashingEverywhere)])
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}
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rb.data_ = new_data
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rb.cur_size_ = buflen
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rb.buffer_ = rb.data_[2:]
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rb.data_[1] = 0
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rb.data_[0] = rb.data_[1]
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for i = 0; i < kSlackForEightByteHashingEverywhere; i++ {
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rb.buffer_[rb.cur_size_+uint32(i)] = 0
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}
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}
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func ringBufferWriteTail(bytes []byte, n uint, rb *ringBuffer) {
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var masked_pos uint = uint(rb.pos_ & rb.mask_)
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if uint32(masked_pos) < rb.tail_size_ {
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/* Just fill the tail buffer with the beginning data. */
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var p uint = uint(rb.size_ + uint32(masked_pos))
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copy(rb.buffer_[p:], bytes[:brotli_min_size_t(n, uint(rb.tail_size_-uint32(masked_pos)))])
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}
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}
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/* Push bytes into the ring buffer. */
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func ringBufferWrite(bytes []byte, n uint, rb *ringBuffer) {
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if rb.pos_ == 0 && uint32(n) < rb.tail_size_ {
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/* Special case for the first write: to process the first block, we don't
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need to allocate the whole ring-buffer and we don't need the tail
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either. However, we do this memory usage optimization only if the
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first write is less than the tail size, which is also the input block
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size, otherwise it is likely that other blocks will follow and we
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will need to reallocate to the full size anyway. */
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rb.pos_ = uint32(n)
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ringBufferInitBuffer(rb.pos_, rb)
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copy(rb.buffer_, bytes[:n])
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return
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}
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if rb.cur_size_ < rb.total_size_ {
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/* Lazily allocate the full buffer. */
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ringBufferInitBuffer(rb.total_size_, rb)
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/* Initialize the last two bytes to zero, so that we don't have to worry
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later when we copy the last two bytes to the first two positions. */
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rb.buffer_[rb.size_-2] = 0
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rb.buffer_[rb.size_-1] = 0
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}
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{
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var masked_pos uint = uint(rb.pos_ & rb.mask_)
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/* The length of the writes is limited so that we do not need to worry
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about a write */
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ringBufferWriteTail(bytes, n, rb)
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if uint32(masked_pos+n) <= rb.size_ {
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/* A single write fits. */
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copy(rb.buffer_[masked_pos:], bytes[:n])
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} else {
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/* Split into two writes.
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Copy into the end of the buffer, including the tail buffer. */
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copy(rb.buffer_[masked_pos:], bytes[:brotli_min_size_t(n, uint(rb.total_size_-uint32(masked_pos)))])
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/* Copy into the beginning of the buffer */
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copy(rb.buffer_, bytes[rb.size_-uint32(masked_pos):][:uint32(n)-(rb.size_-uint32(masked_pos))])
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}
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}
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{
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var not_first_lap bool = rb.pos_&(1<<31) != 0
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var rb_pos_mask uint32 = (1 << 31) - 1
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rb.data_[0] = rb.buffer_[rb.size_-2]
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rb.data_[1] = rb.buffer_[rb.size_-1]
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rb.pos_ = (rb.pos_ & rb_pos_mask) + uint32(uint32(n)&rb_pos_mask)
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if not_first_lap {
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/* Wrap, but preserve not-a-first-lap feature. */
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rb.pos_ |= 1 << 31
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}
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}
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}
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