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267 lines
6.6 KiB
267 lines
6.6 KiB
package brotli
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import "encoding/binary"
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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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/* Bit reading helpers */
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const shortFillBitWindowRead = (8 >> 1)
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var kBitMask = [33]uint32{
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0x00000000,
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0x00000001,
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0x00000003,
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0x00000007,
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0x0000000F,
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0x0000001F,
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0x0000003F,
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0x0000007F,
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0x000000FF,
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0x000001FF,
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0x000003FF,
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0x000007FF,
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0x00000FFF,
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0x00001FFF,
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0x00003FFF,
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0x00007FFF,
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0x0000FFFF,
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0x0001FFFF,
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0x0003FFFF,
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0x0007FFFF,
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0x000FFFFF,
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0x001FFFFF,
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0x003FFFFF,
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0x007FFFFF,
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0x00FFFFFF,
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0x01FFFFFF,
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0x03FFFFFF,
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0x07FFFFFF,
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0x0FFFFFFF,
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0x1FFFFFFF,
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0x3FFFFFFF,
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0x7FFFFFFF,
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0xFFFFFFFF,
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}
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func bitMask(n uint32) uint32 {
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return kBitMask[n]
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}
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type bitReader struct {
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val_ uint64
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bit_pos_ uint32
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input []byte
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input_len uint
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byte_pos uint
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}
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type bitReaderState struct {
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val_ uint64
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bit_pos_ uint32
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input []byte
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input_len uint
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byte_pos uint
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}
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/* Initializes the BrotliBitReader fields. */
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/* Ensures that accumulator is not empty.
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May consume up to sizeof(brotli_reg_t) - 1 bytes of input.
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Returns false if data is required but there is no input available.
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For BROTLI_ALIGNED_READ this function also prepares bit reader for aligned
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reading. */
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func bitReaderSaveState(from *bitReader, to *bitReaderState) {
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to.val_ = from.val_
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to.bit_pos_ = from.bit_pos_
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to.input = from.input
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to.input_len = from.input_len
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to.byte_pos = from.byte_pos
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}
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func bitReaderRestoreState(to *bitReader, from *bitReaderState) {
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to.val_ = from.val_
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to.bit_pos_ = from.bit_pos_
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to.input = from.input
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to.input_len = from.input_len
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to.byte_pos = from.byte_pos
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}
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func getAvailableBits(br *bitReader) uint32 {
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return 64 - br.bit_pos_
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}
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/* Returns amount of unread bytes the bit reader still has buffered from the
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BrotliInput, including whole bytes in br->val_. */
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func getRemainingBytes(br *bitReader) uint {
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return uint(uint32(br.input_len-br.byte_pos) + (getAvailableBits(br) >> 3))
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}
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/* Checks if there is at least |num| bytes left in the input ring-buffer
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(excluding the bits remaining in br->val_). */
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func checkInputAmount(br *bitReader, num uint) bool {
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return br.input_len-br.byte_pos >= num
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}
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/* Guarantees that there are at least |n_bits| + 1 bits in accumulator.
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Precondition: accumulator contains at least 1 bit.
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|n_bits| should be in the range [1..24] for regular build. For portable
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non-64-bit little-endian build only 16 bits are safe to request. */
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func fillBitWindow(br *bitReader, n_bits uint32) {
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if br.bit_pos_ >= 32 {
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br.val_ >>= 32
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br.bit_pos_ ^= 32 /* here same as -= 32 because of the if condition */
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br.val_ |= (uint64(binary.LittleEndian.Uint32(br.input[br.byte_pos:]))) << 32
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br.byte_pos += 4
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}
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}
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/* Mostly like BrotliFillBitWindow, but guarantees only 16 bits and reads no
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more than BROTLI_SHORT_FILL_BIT_WINDOW_READ bytes of input. */
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func fillBitWindow16(br *bitReader) {
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fillBitWindow(br, 17)
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}
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/* Tries to pull one byte of input to accumulator.
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Returns false if there is no input available. */
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func pullByte(br *bitReader) bool {
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if br.byte_pos == br.input_len {
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return false
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}
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br.val_ >>= 8
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br.val_ |= (uint64(br.input[br.byte_pos])) << 56
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br.bit_pos_ -= 8
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br.byte_pos++
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return true
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}
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/* Returns currently available bits.
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The number of valid bits could be calculated by BrotliGetAvailableBits. */
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func getBitsUnmasked(br *bitReader) uint64 {
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return br.val_ >> br.bit_pos_
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}
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/* Like BrotliGetBits, but does not mask the result.
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The result contains at least 16 valid bits. */
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func get16BitsUnmasked(br *bitReader) uint32 {
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fillBitWindow(br, 16)
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return uint32(getBitsUnmasked(br))
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}
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/* Returns the specified number of bits from |br| without advancing bit
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position. */
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func getBits(br *bitReader, n_bits uint32) uint32 {
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fillBitWindow(br, n_bits)
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return uint32(getBitsUnmasked(br)) & bitMask(n_bits)
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}
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/* Tries to peek the specified amount of bits. Returns false, if there
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is not enough input. */
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func safeGetBits(br *bitReader, n_bits uint32, val *uint32) bool {
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for getAvailableBits(br) < n_bits {
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if !pullByte(br) {
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return false
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}
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}
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*val = uint32(getBitsUnmasked(br)) & bitMask(n_bits)
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return true
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}
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/* Advances the bit pos by |n_bits|. */
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func dropBits(br *bitReader, n_bits uint32) {
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br.bit_pos_ += n_bits
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}
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func bitReaderUnload(br *bitReader) {
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var unused_bytes uint32 = getAvailableBits(br) >> 3
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var unused_bits uint32 = unused_bytes << 3
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br.byte_pos -= uint(unused_bytes)
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if unused_bits == 64 {
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br.val_ = 0
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} else {
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br.val_ <<= unused_bits
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}
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br.bit_pos_ += unused_bits
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}
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/* Reads the specified number of bits from |br| and advances the bit pos.
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Precondition: accumulator MUST contain at least |n_bits|. */
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func takeBits(br *bitReader, n_bits uint32, val *uint32) {
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*val = uint32(getBitsUnmasked(br)) & bitMask(n_bits)
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dropBits(br, n_bits)
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}
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/* Reads the specified number of bits from |br| and advances the bit pos.
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Assumes that there is enough input to perform BrotliFillBitWindow. */
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func readBits(br *bitReader, n_bits uint32) uint32 {
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var val uint32
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fillBitWindow(br, n_bits)
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takeBits(br, n_bits, &val)
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return val
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}
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/* Tries to read the specified amount of bits. Returns false, if there
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is not enough input. |n_bits| MUST be positive. */
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func safeReadBits(br *bitReader, n_bits uint32, val *uint32) bool {
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for getAvailableBits(br) < n_bits {
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if !pullByte(br) {
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return false
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}
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}
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takeBits(br, n_bits, val)
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return true
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}
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/* Advances the bit reader position to the next byte boundary and verifies
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that any skipped bits are set to zero. */
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func bitReaderJumpToByteBoundary(br *bitReader) bool {
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var pad_bits_count uint32 = getAvailableBits(br) & 0x7
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var pad_bits uint32 = 0
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if pad_bits_count != 0 {
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takeBits(br, pad_bits_count, &pad_bits)
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}
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return pad_bits == 0
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}
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/* Copies remaining input bytes stored in the bit reader to the output. Value
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|num| may not be larger than BrotliGetRemainingBytes. The bit reader must be
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warmed up again after this. */
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func copyBytes(dest []byte, br *bitReader, num uint) {
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for getAvailableBits(br) >= 8 && num > 0 {
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dest[0] = byte(getBitsUnmasked(br))
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dropBits(br, 8)
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dest = dest[1:]
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num--
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}
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copy(dest, br.input[br.byte_pos:][:num])
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br.byte_pos += num
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}
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func initBitReader(br *bitReader) {
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br.val_ = 0
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br.bit_pos_ = 64
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}
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func warmupBitReader(br *bitReader) bool {
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/* Fixing alignment after unaligned BrotliFillWindow would result accumulator
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overflow. If unalignment is caused by BrotliSafeReadBits, then there is
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enough space in accumulator to fix alignment. */
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if getAvailableBits(br) == 0 {
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if !pullByte(br) {
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return false
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}
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}
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return true
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}
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