forked from mirror/brotli
745 lines
21 KiB
Go
745 lines
21 KiB
Go
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package brotli
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/* Copyright 2015 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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/* Function for fast encoding of an input fragment, independently from the input
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history. This function uses two-pass processing: in the first pass we save
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the found backward matches and literal bytes into a buffer, and in the
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second pass we emit them into the bit stream using prefix codes built based
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on the actual command and literal byte histograms. */
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/* Copyright 2015 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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/* Function for fast encoding of an input fragment, independently from the input
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history. This function uses two-pass processing: in the first pass we save
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the found backward matches and literal bytes into a buffer, and in the
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second pass we emit them into the bit stream using prefix codes built based
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on the actual command and literal byte histograms. */
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var kCompressFragmentTwoPassBlockSize uint = 1 << 17
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func Hash1(p []byte, shift uint, length uint) uint32 {
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var h uint64 = (BROTLI_UNALIGNED_LOAD64LE(p) << ((8 - length) * 8)) * uint64(kHashMul32_a)
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return uint32(h >> shift)
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}
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func HashBytesAtOffset(v uint64, offset uint, shift uint, length uint) uint32 {
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assert(offset <= 8-length)
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{
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var h uint64 = ((v >> (8 * offset)) << ((8 - length) * 8)) * uint64(kHashMul32_a)
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return uint32(h >> shift)
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}
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}
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func IsMatch1(p1 []byte, p2 []byte, length uint) bool {
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var i uint
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for i = 0; i < length && i < 6; i++ {
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if p1[i] != p2[i] {
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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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/* Builds a command and distance prefix code (each 64 symbols) into "depth" and
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"bits" based on "histogram" and stores it into the bit stream. */
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func BuildAndStoreCommandPrefixCode(histogram []uint32, depth []byte, bits []uint16, storage_ix *uint, storage []byte) {
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var tree [129]HuffmanTree
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var cmd_depth = [BROTLI_NUM_COMMAND_SYMBOLS]byte{0}
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/* Tree size for building a tree over 64 symbols is 2 * 64 + 1. */
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var cmd_bits [64]uint16
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BrotliCreateHuffmanTree(histogram, 64, 15, tree[:], depth)
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BrotliCreateHuffmanTree(histogram[64:], 64, 14, tree[:], depth[64:])
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/* We have to jump through a few hoops here in order to compute
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the command bits because the symbols are in a different order than in
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the full alphabet. This looks complicated, but having the symbols
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in this order in the command bits saves a few branches in the Emit*
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functions. */
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copy(cmd_depth[:], depth[24:][:24])
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copy(cmd_depth[24:][:], depth[:8])
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copy(cmd_depth[32:][:], depth[48:][:8])
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copy(cmd_depth[40:][:], depth[8:][:8])
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copy(cmd_depth[48:][:], depth[56:][:8])
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copy(cmd_depth[56:][:], depth[16:][:8])
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BrotliConvertBitDepthsToSymbols(cmd_depth[:], 64, cmd_bits[:])
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copy(bits, cmd_bits[24:][:8])
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copy(bits[8:], cmd_bits[40:][:8])
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copy(bits[16:], cmd_bits[56:][:8])
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copy(bits[24:], cmd_bits[:24])
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copy(bits[48:], cmd_bits[32:][:8])
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copy(bits[56:], cmd_bits[48:][:8])
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BrotliConvertBitDepthsToSymbols(depth[64:], 64, bits[64:])
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{
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/* Create the bit length array for the full command alphabet. */
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var i uint
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for i := 0; i < int(64); i++ {
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cmd_depth[i] = 0
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} /* only 64 first values were used */
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copy(cmd_depth[:], depth[24:][:8])
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copy(cmd_depth[64:][:], depth[32:][:8])
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copy(cmd_depth[128:][:], depth[40:][:8])
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copy(cmd_depth[192:][:], depth[48:][:8])
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copy(cmd_depth[384:][:], depth[56:][:8])
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for i = 0; i < 8; i++ {
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cmd_depth[128+8*i] = depth[i]
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cmd_depth[256+8*i] = depth[8+i]
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cmd_depth[448+8*i] = depth[16+i]
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}
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BrotliStoreHuffmanTree(cmd_depth[:], BROTLI_NUM_COMMAND_SYMBOLS, tree[:], storage_ix, storage)
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}
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BrotliStoreHuffmanTree(depth[64:], 64, tree[:], storage_ix, storage)
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}
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func EmitInsertLen(insertlen uint32, commands *[]uint32) {
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if insertlen < 6 {
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(*commands)[0] = insertlen
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} else if insertlen < 130 {
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var tail uint32 = insertlen - 2
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var nbits uint32 = Log2FloorNonZero(uint(tail)) - 1
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var prefix uint32 = tail >> nbits
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var inscode uint32 = (nbits << 1) + prefix + 2
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var extra uint32 = tail - (prefix << nbits)
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(*commands)[0] = inscode | extra<<8
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} else if insertlen < 2114 {
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var tail uint32 = insertlen - 66
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var nbits uint32 = Log2FloorNonZero(uint(tail))
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var code uint32 = nbits + 10
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var extra uint32 = tail - (1 << nbits)
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(*commands)[0] = code | extra<<8
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} else if insertlen < 6210 {
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var extra uint32 = insertlen - 2114
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(*commands)[0] = 21 | extra<<8
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} else if insertlen < 22594 {
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var extra uint32 = insertlen - 6210
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(*commands)[0] = 22 | extra<<8
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} else {
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var extra uint32 = insertlen - 22594
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(*commands)[0] = 23 | extra<<8
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}
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*commands = (*commands)[1:]
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}
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func EmitCopyLen(copylen uint, commands *[]uint32) {
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if copylen < 10 {
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(*commands)[0] = uint32(copylen + 38)
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} else if copylen < 134 {
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var tail uint = copylen - 6
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var nbits uint = uint(Log2FloorNonZero(tail) - 1)
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var prefix uint = tail >> nbits
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var code uint = (nbits << 1) + prefix + 44
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var extra uint = tail - (prefix << nbits)
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(*commands)[0] = uint32(code | extra<<8)
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} else if copylen < 2118 {
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var tail uint = copylen - 70
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var nbits uint = uint(Log2FloorNonZero(tail))
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var code uint = nbits + 52
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var extra uint = tail - (uint(1) << nbits)
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(*commands)[0] = uint32(code | extra<<8)
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} else {
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var extra uint = copylen - 2118
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(*commands)[0] = uint32(63 | extra<<8)
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}
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*commands = (*commands)[1:]
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}
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func EmitCopyLenLastDistance(copylen uint, commands *[]uint32) {
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if copylen < 12 {
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(*commands)[0] = uint32(copylen + 20)
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*commands = (*commands)[1:]
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} else if copylen < 72 {
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var tail uint = copylen - 8
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var nbits uint = uint(Log2FloorNonZero(tail) - 1)
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var prefix uint = tail >> nbits
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var code uint = (nbits << 1) + prefix + 28
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var extra uint = tail - (prefix << nbits)
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(*commands)[0] = uint32(code | extra<<8)
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*commands = (*commands)[1:]
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} else if copylen < 136 {
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var tail uint = copylen - 8
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var code uint = (tail >> 5) + 54
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var extra uint = tail & 31
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(*commands)[0] = uint32(code | extra<<8)
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*commands = (*commands)[1:]
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(*commands)[0] = 64
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*commands = (*commands)[1:]
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} else if copylen < 2120 {
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var tail uint = copylen - 72
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var nbits uint = uint(Log2FloorNonZero(tail))
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var code uint = nbits + 52
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var extra uint = tail - (uint(1) << nbits)
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(*commands)[0] = uint32(code | extra<<8)
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*commands = (*commands)[1:]
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(*commands)[0] = 64
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*commands = (*commands)[1:]
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} else {
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var extra uint = copylen - 2120
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(*commands)[0] = uint32(63 | extra<<8)
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*commands = (*commands)[1:]
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(*commands)[0] = 64
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*commands = (*commands)[1:]
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}
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}
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func EmitDistance(distance uint32, commands *[]uint32) {
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var d uint32 = distance + 3
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var nbits uint32 = Log2FloorNonZero(uint(d)) - 1
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var prefix uint32 = (d >> nbits) & 1
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var offset uint32 = (2 + prefix) << nbits
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var distcode uint32 = 2*(nbits-1) + prefix + 80
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var extra uint32 = d - offset
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(*commands)[0] = distcode | extra<<8
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*commands = (*commands)[1:]
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}
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/* REQUIRES: len <= 1 << 24. */
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func BrotliStoreMetaBlockHeader(len uint, is_uncompressed bool, storage_ix *uint, storage []byte) {
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var nibbles uint = 6
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/* ISLAST */
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BrotliWriteBits(1, 0, storage_ix, storage)
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if len <= 1<<16 {
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nibbles = 4
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} else if len <= 1<<20 {
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nibbles = 5
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}
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BrotliWriteBits(2, uint64(nibbles)-4, storage_ix, storage)
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BrotliWriteBits(nibbles*4, uint64(len)-1, storage_ix, storage)
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/* ISUNCOMPRESSED */
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BrotliWriteSingleBit(is_uncompressed, storage_ix, storage)
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}
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func CreateCommands(input []byte, block_size uint, input_size uint, base_ip_ptr []byte, table []int, table_bits uint, min_match uint, literals *[]byte, commands *[]uint32) {
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var ip int = 0
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var shift uint = 64 - table_bits
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var ip_end int = int(block_size)
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var base_ip int = -cap(base_ip_ptr) + cap(input)
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var next_emit int = 0
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var last_distance int = -1
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/* "ip" is the input pointer. */
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var kInputMarginBytes uint = BROTLI_WINDOW_GAP
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/* "next_emit" is a pointer to the first byte that is not covered by a
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previous copy. Bytes between "next_emit" and the start of the next copy or
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the end of the input will be emitted as literal bytes. */
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if block_size >= kInputMarginBytes {
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var len_limit uint = brotli_min_size_t(block_size-min_match, input_size-kInputMarginBytes)
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var ip_limit int = int(len_limit)
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/* For the last block, we need to keep a 16 bytes margin so that we can be
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sure that all distances are at most window size - 16.
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For all other blocks, we only need to keep a margin of 5 bytes so that
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we don't go over the block size with a copy. */
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var next_hash uint32
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ip++
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for next_hash = Hash1(input[ip:], shift, min_match); ; {
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var skip uint32 = 32
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var next_ip int = ip
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/* Step 1: Scan forward in the input looking for a 6-byte-long match.
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If we get close to exhausting the input then goto emit_remainder.
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Heuristic match skipping: If 32 bytes are scanned with no matches
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found, start looking only at every other byte. If 32 more bytes are
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scanned, look at every third byte, etc.. When a match is found,
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immediately go back to looking at every byte. This is a small loss
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(~5% performance, ~0.1% density) for compressible data due to more
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bookkeeping, but for non-compressible data (such as JPEG) it's a huge
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win since the compressor quickly "realizes" the data is incompressible
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and doesn't bother looking for matches everywhere.
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The "skip" variable keeps track of how many bytes there are since the
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last match; dividing it by 32 (ie. right-shifting by five) gives the
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number of bytes to move ahead for each iteration. */
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var candidate int
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assert(next_emit < ip)
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trawl:
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for {
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var hash uint32 = next_hash
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var bytes_between_hash_lookups uint32 = skip >> 5
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skip++
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ip = next_ip
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assert(hash == Hash1(input[ip:], shift, min_match))
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next_ip = int(uint32(ip) + bytes_between_hash_lookups)
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if next_ip > ip_limit {
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goto emit_remainder
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}
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next_hash = Hash1(input[next_ip:], shift, min_match)
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candidate = ip - last_distance
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if IsMatch1(input[ip:], input[candidate:], min_match) {
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if candidate < ip {
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table[hash] = int(ip - base_ip)
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break
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}
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}
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candidate = base_ip + table[hash]
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assert(candidate >= base_ip)
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assert(candidate < ip)
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table[hash] = int(ip - base_ip)
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if !(!IsMatch1(input[ip:], input[candidate:], min_match)) {
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break
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}
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}
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/* Check copy distance. If candidate is not feasible, continue search.
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Checking is done outside of hot loop to reduce overhead. */
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if ip-candidate > MAX_DISTANCE {
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goto trawl
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}
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/* Step 2: Emit the found match together with the literal bytes from
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"next_emit", and then see if we can find a next match immediately
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afterwards. Repeat until we find no match for the input
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without emitting some literal bytes. */
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{
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var base int = ip
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/* > 0 */
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var matched uint = min_match + FindMatchLengthWithLimit(input[uint(candidate)+min_match:], input[uint(ip)+min_match:], uint(ip_end-ip)-min_match)
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var distance int = int(base - candidate)
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/* We have a 6-byte match at ip, and we need to emit bytes in
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[next_emit, ip). */
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var insert int = int(base - next_emit)
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ip += int(matched)
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EmitInsertLen(uint32(insert), commands)
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copy(*literals, input[next_emit:][:uint(insert)])
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*literals = (*literals)[insert:]
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if distance == last_distance {
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(*commands)[0] = 64
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*commands = (*commands)[1:]
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} else {
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EmitDistance(uint32(distance), commands)
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last_distance = distance
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}
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EmitCopyLenLastDistance(matched, commands)
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next_emit = ip
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if ip >= ip_limit {
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goto emit_remainder
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}
|
||
|
|
{
|
||
|
|
var input_bytes uint64
|
||
|
|
var cur_hash uint32
|
||
|
|
/* We could immediately start working at ip now, but to improve
|
||
|
|
compression we first update "table" with the hashes of some
|
||
|
|
positions within the last copy. */
|
||
|
|
|
||
|
|
var prev_hash uint32
|
||
|
|
if min_match == 4 {
|
||
|
|
input_bytes = BROTLI_UNALIGNED_LOAD64LE(input[ip-3:])
|
||
|
|
cur_hash = HashBytesAtOffset(input_bytes, 3, shift, min_match)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 3)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 1, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 2)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 1)
|
||
|
|
} else {
|
||
|
|
input_bytes = BROTLI_UNALIGNED_LOAD64LE(input[ip-5:])
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 5)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 1, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 4)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 2, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 3)
|
||
|
|
input_bytes = BROTLI_UNALIGNED_LOAD64LE(input[ip-2:])
|
||
|
|
cur_hash = HashBytesAtOffset(input_bytes, 2, shift, min_match)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 2)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 1, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 1)
|
||
|
|
}
|
||
|
|
|
||
|
|
candidate = base_ip + table[cur_hash]
|
||
|
|
table[cur_hash] = int(ip - base_ip)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
for ip-candidate <= MAX_DISTANCE && IsMatch1(input[ip:], input[candidate:], min_match) {
|
||
|
|
var base int = ip
|
||
|
|
/* We have a 6-byte match at ip, and no need to emit any
|
||
|
|
literal bytes prior to ip. */
|
||
|
|
|
||
|
|
var matched uint = min_match + FindMatchLengthWithLimit(input[uint(candidate)+min_match:], input[uint(ip)+min_match:], uint(ip_end-ip)-min_match)
|
||
|
|
ip += int(matched)
|
||
|
|
last_distance = int(base - candidate) /* > 0 */
|
||
|
|
EmitCopyLen(matched, commands)
|
||
|
|
EmitDistance(uint32(last_distance), commands)
|
||
|
|
|
||
|
|
next_emit = ip
|
||
|
|
if ip >= ip_limit {
|
||
|
|
goto emit_remainder
|
||
|
|
}
|
||
|
|
{
|
||
|
|
var input_bytes uint64
|
||
|
|
var cur_hash uint32
|
||
|
|
/* We could immediately start working at ip now, but to improve
|
||
|
|
compression we first update "table" with the hashes of some
|
||
|
|
positions within the last copy. */
|
||
|
|
|
||
|
|
var prev_hash uint32
|
||
|
|
if min_match == 4 {
|
||
|
|
input_bytes = BROTLI_UNALIGNED_LOAD64LE(input[ip-3:])
|
||
|
|
cur_hash = HashBytesAtOffset(input_bytes, 3, shift, min_match)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 3)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 1, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 2)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 2, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 1)
|
||
|
|
} else {
|
||
|
|
input_bytes = BROTLI_UNALIGNED_LOAD64LE(input[ip-5:])
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 5)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 1, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 4)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 2, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 3)
|
||
|
|
input_bytes = BROTLI_UNALIGNED_LOAD64LE(input[ip-2:])
|
||
|
|
cur_hash = HashBytesAtOffset(input_bytes, 2, shift, min_match)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 0, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 2)
|
||
|
|
prev_hash = HashBytesAtOffset(input_bytes, 1, shift, min_match)
|
||
|
|
table[prev_hash] = int(ip - base_ip - 1)
|
||
|
|
}
|
||
|
|
|
||
|
|
candidate = base_ip + table[cur_hash]
|
||
|
|
table[cur_hash] = int(ip - base_ip)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
ip++
|
||
|
|
next_hash = Hash1(input[ip:], shift, min_match)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
emit_remainder:
|
||
|
|
assert(next_emit <= ip_end)
|
||
|
|
|
||
|
|
/* Emit the remaining bytes as literals. */
|
||
|
|
if next_emit < ip_end {
|
||
|
|
var insert uint32 = uint32(ip_end - next_emit)
|
||
|
|
EmitInsertLen(insert, commands)
|
||
|
|
copy(*literals, input[next_emit:][:insert])
|
||
|
|
*literals = (*literals)[insert:]
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
var StoreCommands_kNumExtraBits = [128]uint32{
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
1,
|
||
|
|
1,
|
||
|
|
2,
|
||
|
|
2,
|
||
|
|
3,
|
||
|
|
3,
|
||
|
|
4,
|
||
|
|
4,
|
||
|
|
5,
|
||
|
|
5,
|
||
|
|
6,
|
||
|
|
7,
|
||
|
|
8,
|
||
|
|
9,
|
||
|
|
10,
|
||
|
|
12,
|
||
|
|
14,
|
||
|
|
24,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
1,
|
||
|
|
1,
|
||
|
|
2,
|
||
|
|
2,
|
||
|
|
3,
|
||
|
|
3,
|
||
|
|
4,
|
||
|
|
4,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
1,
|
||
|
|
1,
|
||
|
|
2,
|
||
|
|
2,
|
||
|
|
3,
|
||
|
|
3,
|
||
|
|
4,
|
||
|
|
4,
|
||
|
|
5,
|
||
|
|
5,
|
||
|
|
6,
|
||
|
|
7,
|
||
|
|
8,
|
||
|
|
9,
|
||
|
|
10,
|
||
|
|
24,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
0,
|
||
|
|
1,
|
||
|
|
1,
|
||
|
|
2,
|
||
|
|
2,
|
||
|
|
3,
|
||
|
|
3,
|
||
|
|
4,
|
||
|
|
4,
|
||
|
|
5,
|
||
|
|
5,
|
||
|
|
6,
|
||
|
|
6,
|
||
|
|
7,
|
||
|
|
7,
|
||
|
|
8,
|
||
|
|
8,
|
||
|
|
9,
|
||
|
|
9,
|
||
|
|
10,
|
||
|
|
10,
|
||
|
|
11,
|
||
|
|
11,
|
||
|
|
12,
|
||
|
|
12,
|
||
|
|
13,
|
||
|
|
13,
|
||
|
|
14,
|
||
|
|
14,
|
||
|
|
15,
|
||
|
|
15,
|
||
|
|
16,
|
||
|
|
16,
|
||
|
|
17,
|
||
|
|
17,
|
||
|
|
18,
|
||
|
|
18,
|
||
|
|
19,
|
||
|
|
19,
|
||
|
|
20,
|
||
|
|
20,
|
||
|
|
21,
|
||
|
|
21,
|
||
|
|
22,
|
||
|
|
22,
|
||
|
|
23,
|
||
|
|
23,
|
||
|
|
24,
|
||
|
|
24,
|
||
|
|
}
|
||
|
|
var StoreCommands_kInsertOffset = [24]uint32{
|
||
|
|
0,
|
||
|
|
1,
|
||
|
|
2,
|
||
|
|
3,
|
||
|
|
4,
|
||
|
|
5,
|
||
|
|
6,
|
||
|
|
8,
|
||
|
|
10,
|
||
|
|
14,
|
||
|
|
18,
|
||
|
|
26,
|
||
|
|
34,
|
||
|
|
50,
|
||
|
|
66,
|
||
|
|
98,
|
||
|
|
130,
|
||
|
|
194,
|
||
|
|
322,
|
||
|
|
578,
|
||
|
|
1090,
|
||
|
|
2114,
|
||
|
|
6210,
|
||
|
|
22594,
|
||
|
|
}
|
||
|
|
|
||
|
|
func StoreCommands(literals []byte, num_literals uint, commands []uint32, num_commands uint, storage_ix *uint, storage []byte) {
|
||
|
|
var lit_depths [256]byte
|
||
|
|
var lit_bits [256]uint16
|
||
|
|
var lit_histo = [256]uint32{0}
|
||
|
|
var cmd_depths = [128]byte{0}
|
||
|
|
var cmd_bits = [128]uint16{0}
|
||
|
|
var cmd_histo = [128]uint32{0}
|
||
|
|
var i uint
|
||
|
|
for i = 0; i < num_literals; i++ {
|
||
|
|
lit_histo[literals[i]]++
|
||
|
|
}
|
||
|
|
|
||
|
|
BrotliBuildAndStoreHuffmanTreeFast(lit_histo[:], num_literals, /* max_bits = */
|
||
|
|
8, lit_depths[:], lit_bits[:], storage_ix, storage)
|
||
|
|
|
||
|
|
for i = 0; i < num_commands; i++ {
|
||
|
|
var code uint32 = commands[i] & 0xFF
|
||
|
|
assert(code < 128)
|
||
|
|
cmd_histo[code]++
|
||
|
|
}
|
||
|
|
|
||
|
|
cmd_histo[1] += 1
|
||
|
|
cmd_histo[2] += 1
|
||
|
|
cmd_histo[64] += 1
|
||
|
|
cmd_histo[84] += 1
|
||
|
|
BuildAndStoreCommandPrefixCode(cmd_histo[:], cmd_depths[:], cmd_bits[:], storage_ix, storage)
|
||
|
|
|
||
|
|
for i = 0; i < num_commands; i++ {
|
||
|
|
var cmd uint32 = commands[i]
|
||
|
|
var code uint32 = cmd & 0xFF
|
||
|
|
var extra uint32 = cmd >> 8
|
||
|
|
assert(code < 128)
|
||
|
|
BrotliWriteBits(uint(cmd_depths[code]), uint64(cmd_bits[code]), storage_ix, storage)
|
||
|
|
BrotliWriteBits(uint(StoreCommands_kNumExtraBits[code]), uint64(extra), storage_ix, storage)
|
||
|
|
if code < 24 {
|
||
|
|
var insert uint32 = StoreCommands_kInsertOffset[code] + extra
|
||
|
|
var j uint32
|
||
|
|
for j = 0; j < insert; j++ {
|
||
|
|
var lit byte = literals[0]
|
||
|
|
BrotliWriteBits(uint(lit_depths[lit]), uint64(lit_bits[lit]), storage_ix, storage)
|
||
|
|
literals = literals[1:]
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
/* Acceptable loss for uncompressible speedup is 2% */
|
||
|
|
const MIN_RATIO = 0.98
|
||
|
|
|
||
|
|
const SAMPLE_RATE = 43
|
||
|
|
|
||
|
|
func ShouldCompress(input []byte, input_size uint, num_literals uint) bool {
|
||
|
|
var corpus_size float64 = float64(input_size)
|
||
|
|
if float64(num_literals) < MIN_RATIO*corpus_size {
|
||
|
|
return true
|
||
|
|
} else {
|
||
|
|
var literal_histo = [256]uint32{0}
|
||
|
|
var max_total_bit_cost float64 = corpus_size * 8 * MIN_RATIO / SAMPLE_RATE
|
||
|
|
var i uint
|
||
|
|
for i = 0; i < input_size; i += SAMPLE_RATE {
|
||
|
|
literal_histo[input[i]]++
|
||
|
|
}
|
||
|
|
|
||
|
|
return BitsEntropy(literal_histo[:], 256) < max_total_bit_cost
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func RewindBitPosition(new_storage_ix uint, storage_ix *uint, storage []byte) {
|
||
|
|
var bitpos uint = new_storage_ix & 7
|
||
|
|
var mask uint = (1 << bitpos) - 1
|
||
|
|
storage[new_storage_ix>>3] &= byte(mask)
|
||
|
|
*storage_ix = new_storage_ix
|
||
|
|
}
|
||
|
|
|
||
|
|
func EmitUncompressedMetaBlock(input []byte, input_size uint, storage_ix *uint, storage []byte) {
|
||
|
|
BrotliStoreMetaBlockHeader(input_size, true, storage_ix, storage)
|
||
|
|
*storage_ix = (*storage_ix + 7) &^ 7
|
||
|
|
copy(storage[*storage_ix>>3:], input[:input_size])
|
||
|
|
*storage_ix += input_size << 3
|
||
|
|
storage[*storage_ix>>3] = 0
|
||
|
|
}
|
||
|
|
|
||
|
|
func BrotliCompressFragmentTwoPassImpl(input []byte, input_size uint, is_last bool, command_buf []uint32, literal_buf []byte, table []int, table_bits uint, min_match uint, storage_ix *uint, storage []byte) {
|
||
|
|
/* Save the start of the first block for position and distance computations.
|
||
|
|
*/
|
||
|
|
var base_ip []byte = input
|
||
|
|
|
||
|
|
for input_size > 0 {
|
||
|
|
var block_size uint = brotli_min_size_t(input_size, kCompressFragmentTwoPassBlockSize)
|
||
|
|
var commands []uint32 = command_buf
|
||
|
|
var literals []byte = literal_buf
|
||
|
|
var num_literals uint
|
||
|
|
CreateCommands(input, block_size, input_size, base_ip, table, table_bits, min_match, &literals, &commands)
|
||
|
|
num_literals = uint(-cap(literals) + cap(literal_buf))
|
||
|
|
if ShouldCompress(input, block_size, num_literals) {
|
||
|
|
var num_commands uint = uint(-cap(commands) + cap(command_buf))
|
||
|
|
BrotliStoreMetaBlockHeader(block_size, false, storage_ix, storage)
|
||
|
|
|
||
|
|
/* No block splits, no contexts. */
|
||
|
|
BrotliWriteBits(13, 0, storage_ix, storage)
|
||
|
|
|
||
|
|
StoreCommands(literal_buf, num_literals, command_buf, num_commands, storage_ix, storage)
|
||
|
|
} else {
|
||
|
|
/* Since we did not find many backward references and the entropy of
|
||
|
|
the data is close to 8 bits, we can simply emit an uncompressed block.
|
||
|
|
This makes compression speed of uncompressible data about 3x faster. */
|
||
|
|
EmitUncompressedMetaBlock(input, block_size, storage_ix, storage)
|
||
|
|
}
|
||
|
|
|
||
|
|
input = input[block_size:]
|
||
|
|
input_size -= block_size
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
func BrotliCompressFragmentTwoPass(input []byte, input_size uint, is_last bool, command_buf []uint32, literal_buf []byte, table []int, table_size uint, storage_ix *uint, storage []byte) {
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var initial_storage_ix uint = *storage_ix
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var table_bits uint = uint(Log2FloorNonZero(table_size))
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var min_match uint
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if table_bits <= 15 {
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min_match = 4
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} else {
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min_match = 6
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}
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BrotliCompressFragmentTwoPassImpl(input, input_size, is_last, command_buf, literal_buf, table, table_bits, min_match, storage_ix, storage)
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/* If output is larger than single uncompressed block, rewrite it. */
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if *storage_ix-initial_storage_ix > 31+(input_size<<3) {
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RewindBitPosition(initial_storage_ix, storage_ix, storage)
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EmitUncompressedMetaBlock(input, input_size, storage_ix, storage)
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}
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if is_last {
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BrotliWriteBits(1, 1, storage_ix, storage) /* islast */
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BrotliWriteBits(1, 1, storage_ix, storage) /* isempty */
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*storage_ix = (*storage_ix + 7) &^ 7
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}
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}
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