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package brotli
import "encoding/binary"
/* Copyright 2013 Google Inc. All Rights Reserved.
Distributed under MIT license.
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
*/
/* Bit reading helpers */
const shortFillBitWindowRead = (8 >> 1)
var kBitMask = [33]uint32{
0x00000000,
0x00000001,
0x00000003,
0x00000007,
0x0000000F,
0x0000001F,
0x0000003F,
0x0000007F,
0x000000FF,
0x000001FF,
0x000003FF,
0x000007FF,
0x00000FFF,
0x00001FFF,
0x00003FFF,
0x00007FFF,
0x0000FFFF,
0x0001FFFF,
0x0003FFFF,
0x0007FFFF,
0x000FFFFF,
0x001FFFFF,
0x003FFFFF,
0x007FFFFF,
0x00FFFFFF,
0x01FFFFFF,
0x03FFFFFF,
0x07FFFFFF,
0x0FFFFFFF,
0x1FFFFFFF,
0x3FFFFFFF,
0x7FFFFFFF,
0xFFFFFFFF,
}
func bitMask(n uint32) uint32 {
return kBitMask[n]
}
type bitReader struct {
val_ uint64
bit_pos_ uint32
input []byte
input_len uint
byte_pos uint
}
type bitReaderState struct {
val_ uint64
bit_pos_ uint32
input []byte
input_len uint
byte_pos uint
}
/* Initializes the BrotliBitReader fields. */
/* Ensures that accumulator is not empty.
May consume up to sizeof(brotli_reg_t) - 1 bytes of input.
Returns false if data is required but there is no input available.
For BROTLI_ALIGNED_READ this function also prepares bit reader for aligned
reading. */
func bitReaderSaveState(from *bitReader, to *bitReaderState) {
to.val_ = from.val_
to.bit_pos_ = from.bit_pos_
to.input = from.input
to.input_len = from.input_len
to.byte_pos = from.byte_pos
}
func bitReaderRestoreState(to *bitReader, from *bitReaderState) {
to.val_ = from.val_
to.bit_pos_ = from.bit_pos_
to.input = from.input
to.input_len = from.input_len
to.byte_pos = from.byte_pos
}
func getAvailableBits(br *bitReader) uint32 {
return 64 - br.bit_pos_
}
/* Returns amount of unread bytes the bit reader still has buffered from the
BrotliInput, including whole bytes in br->val_. */
func getRemainingBytes(br *bitReader) uint {
return uint(uint32(br.input_len-br.byte_pos) + (getAvailableBits(br) >> 3))
}
/* Checks if there is at least |num| bytes left in the input ring-buffer
(excluding the bits remaining in br->val_). */
func checkInputAmount(br *bitReader, num uint) bool {
return br.input_len-br.byte_pos >= num
}
/* Guarantees that there are at least |n_bits| + 1 bits in accumulator.
Precondition: accumulator contains at least 1 bit.
|n_bits| should be in the range [1..24] for regular build. For portable
non-64-bit little-endian build only 16 bits are safe to request. */
func fillBitWindow(br *bitReader, n_bits uint32) {
if br.bit_pos_ >= 32 {
br.val_ >>= 32
br.bit_pos_ ^= 32 /* here same as -= 32 because of the if condition */
br.val_ |= (uint64(binary.LittleEndian.Uint32(br.input[br.byte_pos:]))) << 32
br.byte_pos += 4
}
}
/* Mostly like BrotliFillBitWindow, but guarantees only 16 bits and reads no
more than BROTLI_SHORT_FILL_BIT_WINDOW_READ bytes of input. */
func fillBitWindow16(br *bitReader) {
fillBitWindow(br, 17)
}
/* Tries to pull one byte of input to accumulator.
Returns false if there is no input available. */
func pullByte(br *bitReader) bool {
if br.byte_pos == br.input_len {
return false
}
br.val_ >>= 8
br.val_ |= (uint64(br.input[br.byte_pos])) << 56
br.bit_pos_ -= 8
br.byte_pos++
return true
}
/* Returns currently available bits.
The number of valid bits could be calculated by BrotliGetAvailableBits. */
func getBitsUnmasked(br *bitReader) uint64 {
return br.val_ >> br.bit_pos_
}
/* Like BrotliGetBits, but does not mask the result.
The result contains at least 16 valid bits. */
func get16BitsUnmasked(br *bitReader) uint32 {
fillBitWindow(br, 16)
return uint32(getBitsUnmasked(br))
}
/* Returns the specified number of bits from |br| without advancing bit
position. */
func getBits(br *bitReader, n_bits uint32) uint32 {
fillBitWindow(br, n_bits)
return uint32(getBitsUnmasked(br)) & bitMask(n_bits)
}
/* Tries to peek the specified amount of bits. Returns false, if there
is not enough input. */
func safeGetBits(br *bitReader, n_bits uint32, val *uint32) bool {
for getAvailableBits(br) < n_bits {
if !pullByte(br) {
return false
}
}
*val = uint32(getBitsUnmasked(br)) & bitMask(n_bits)
return true
}
/* Advances the bit pos by |n_bits|. */
func dropBits(br *bitReader, n_bits uint32) {
br.bit_pos_ += n_bits
}
func bitReaderUnload(br *bitReader) {
var unused_bytes uint32 = getAvailableBits(br) >> 3
var unused_bits uint32 = unused_bytes << 3
br.byte_pos -= uint(unused_bytes)
if unused_bits == 64 {
br.val_ = 0
} else {
br.val_ <<= unused_bits
}
br.bit_pos_ += unused_bits
}
/* Reads the specified number of bits from |br| and advances the bit pos.
Precondition: accumulator MUST contain at least |n_bits|. */
func takeBits(br *bitReader, n_bits uint32, val *uint32) {
*val = uint32(getBitsUnmasked(br)) & bitMask(n_bits)
dropBits(br, n_bits)
}
/* Reads the specified number of bits from |br| and advances the bit pos.
Assumes that there is enough input to perform BrotliFillBitWindow. */
func readBits(br *bitReader, n_bits uint32) uint32 {
var val uint32
fillBitWindow(br, n_bits)
takeBits(br, n_bits, &val)
return val
}
/* Tries to read the specified amount of bits. Returns false, if there
is not enough input. |n_bits| MUST be positive. */
func safeReadBits(br *bitReader, n_bits uint32, val *uint32) bool {
for getAvailableBits(br) < n_bits {
if !pullByte(br) {
return false
}
}
takeBits(br, n_bits, val)
return true
}
/* Advances the bit reader position to the next byte boundary and verifies
that any skipped bits are set to zero. */
func bitReaderJumpToByteBoundary(br *bitReader) bool {
var pad_bits_count uint32 = getAvailableBits(br) & 0x7
var pad_bits uint32 = 0
if pad_bits_count != 0 {
takeBits(br, pad_bits_count, &pad_bits)
}
return pad_bits == 0
}
/* Copies remaining input bytes stored in the bit reader to the output. Value
|num| may not be larger than BrotliGetRemainingBytes. The bit reader must be
warmed up again after this. */
func copyBytes(dest []byte, br *bitReader, num uint) {
for getAvailableBits(br) >= 8 && num > 0 {
dest[0] = byte(getBitsUnmasked(br))
dropBits(br, 8)
dest = dest[1:]
num--
}
copy(dest, br.input[br.byte_pos:][:num])
br.byte_pos += num
}
func initBitReader(br *bitReader) {
br.val_ = 0
br.bit_pos_ = 64
}
func warmupBitReader(br *bitReader) bool {
/* Fixing alignment after unaligned BrotliFillWindow would result accumulator
overflow. If unalignment is caused by BrotliSafeReadBits, then there is
enough space in accumulator to fix alignment. */
if getAvailableBits(br) == 0 {
if !pullByte(br) {
return false
}
}
return true
}
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