774 lines
22 KiB
Go
774 lines
22 KiB
Go
package brotli
|
|
|
|
import "encoding/binary"
|
|
|
|
/* Copyright 2015 Google Inc. All Rights Reserved.
|
|
|
|
Distributed under MIT license.
|
|
See file LICENSE for detail or copy at https://opensource.org/licenses/MIT
|
|
*/
|
|
|
|
/* Function for fast encoding of an input fragment, independently from the input
|
|
history. This function uses two-pass processing: in the first pass we save
|
|
the found backward matches and literal bytes into a buffer, and in the
|
|
second pass we emit them into the bit stream using prefix codes built based
|
|
on the actual command and literal byte histograms. */
|
|
|
|
const kCompressFragmentTwoPassBlockSize uint = 1 << 17
|
|
|
|
func hash1(p []byte, shift uint, length uint) uint32 {
|
|
var h uint64 = (binary.LittleEndian.Uint64(p) << ((8 - length) * 8)) * uint64(kHashMul32)
|
|
return uint32(h >> shift)
|
|
}
|
|
|
|
func hashBytesAtOffset(v uint64, offset uint, shift uint, length uint) uint32 {
|
|
assert(offset <= 8-length)
|
|
{
|
|
var h uint64 = ((v >> (8 * offset)) << ((8 - length) * 8)) * uint64(kHashMul32)
|
|
return uint32(h >> shift)
|
|
}
|
|
}
|
|
|
|
func isMatch1(p1 []byte, p2 []byte, length uint) bool {
|
|
if binary.LittleEndian.Uint32(p1) != binary.LittleEndian.Uint32(p2) {
|
|
return false
|
|
}
|
|
if length == 4 {
|
|
return true
|
|
}
|
|
return p1[4] == p2[4] && p1[5] == p2[5]
|
|
}
|
|
|
|
/*
|
|
Builds a command and distance prefix code (each 64 symbols) into "depth" and
|
|
|
|
"bits" based on "histogram" and stores it into the bit stream.
|
|
*/
|
|
func buildAndStoreCommandPrefixCode(histogram []uint32, depth []byte, bits []uint16, storage_ix *uint, storage []byte) {
|
|
var tree [129]huffmanTree
|
|
var cmd_depth = [numCommandSymbols]byte{0}
|
|
/* Tree size for building a tree over 64 symbols is 2 * 64 + 1. */
|
|
|
|
var cmd_bits [64]uint16
|
|
createHuffmanTree(histogram, 64, 15, tree[:], depth)
|
|
createHuffmanTree(histogram[64:], 64, 14, tree[:], depth[64:])
|
|
|
|
/* We have to jump through a few hoops here in order to compute
|
|
the command bits because the symbols are in a different order than in
|
|
the full alphabet. This looks complicated, but having the symbols
|
|
in this order in the command bits saves a few branches in the Emit*
|
|
functions. */
|
|
copy(cmd_depth[:], depth[24:][:24])
|
|
|
|
copy(cmd_depth[24:][:], depth[:8])
|
|
copy(cmd_depth[32:][:], depth[48:][:8])
|
|
copy(cmd_depth[40:][:], depth[8:][:8])
|
|
copy(cmd_depth[48:][:], depth[56:][:8])
|
|
copy(cmd_depth[56:][:], depth[16:][:8])
|
|
convertBitDepthsToSymbols(cmd_depth[:], 64, cmd_bits[:])
|
|
copy(bits, cmd_bits[24:][:8])
|
|
copy(bits[8:], cmd_bits[40:][:8])
|
|
copy(bits[16:], cmd_bits[56:][:8])
|
|
copy(bits[24:], cmd_bits[:24])
|
|
copy(bits[48:], cmd_bits[32:][:8])
|
|
copy(bits[56:], cmd_bits[48:][:8])
|
|
convertBitDepthsToSymbols(depth[64:], 64, bits[64:])
|
|
{
|
|
/* Create the bit length array for the full command alphabet. */
|
|
var i uint
|
|
for i := 0; i < int(64); i++ {
|
|
cmd_depth[i] = 0
|
|
} /* only 64 first values were used */
|
|
copy(cmd_depth[:], depth[24:][:8])
|
|
copy(cmd_depth[64:][:], depth[32:][:8])
|
|
copy(cmd_depth[128:][:], depth[40:][:8])
|
|
copy(cmd_depth[192:][:], depth[48:][:8])
|
|
copy(cmd_depth[384:][:], depth[56:][:8])
|
|
for i = 0; i < 8; i++ {
|
|
cmd_depth[128+8*i] = depth[i]
|
|
cmd_depth[256+8*i] = depth[8+i]
|
|
cmd_depth[448+8*i] = depth[16+i]
|
|
}
|
|
|
|
storeHuffmanTree(cmd_depth[:], numCommandSymbols, tree[:], storage_ix, storage)
|
|
}
|
|
|
|
storeHuffmanTree(depth[64:], 64, tree[:], storage_ix, storage)
|
|
}
|
|
|
|
func emitInsertLen(insertlen uint32, commands *[]uint32) {
|
|
if insertlen < 6 {
|
|
(*commands)[0] = insertlen
|
|
} else if insertlen < 130 {
|
|
var tail uint32 = insertlen - 2
|
|
var nbits uint32 = log2FloorNonZero(uint(tail)) - 1
|
|
var prefix uint32 = tail >> nbits
|
|
var inscode uint32 = (nbits << 1) + prefix + 2
|
|
var extra uint32 = tail - (prefix << nbits)
|
|
(*commands)[0] = inscode | extra<<8
|
|
} else if insertlen < 2114 {
|
|
var tail uint32 = insertlen - 66
|
|
var nbits uint32 = log2FloorNonZero(uint(tail))
|
|
var code uint32 = nbits + 10
|
|
var extra uint32 = tail - (1 << nbits)
|
|
(*commands)[0] = code | extra<<8
|
|
} else if insertlen < 6210 {
|
|
var extra uint32 = insertlen - 2114
|
|
(*commands)[0] = 21 | extra<<8
|
|
} else if insertlen < 22594 {
|
|
var extra uint32 = insertlen - 6210
|
|
(*commands)[0] = 22 | extra<<8
|
|
} else {
|
|
var extra uint32 = insertlen - 22594
|
|
(*commands)[0] = 23 | extra<<8
|
|
}
|
|
|
|
*commands = (*commands)[1:]
|
|
}
|
|
|
|
func emitCopyLen(copylen uint, commands *[]uint32) {
|
|
if copylen < 10 {
|
|
(*commands)[0] = uint32(copylen + 38)
|
|
} else if copylen < 134 {
|
|
var tail uint = copylen - 6
|
|
var nbits uint = uint(log2FloorNonZero(tail) - 1)
|
|
var prefix uint = tail >> nbits
|
|
var code uint = (nbits << 1) + prefix + 44
|
|
var extra uint = tail - (prefix << nbits)
|
|
(*commands)[0] = uint32(code | extra<<8)
|
|
} else if copylen < 2118 {
|
|
var tail uint = copylen - 70
|
|
var nbits uint = uint(log2FloorNonZero(tail))
|
|
var code uint = nbits + 52
|
|
var extra uint = tail - (uint(1) << nbits)
|
|
(*commands)[0] = uint32(code | extra<<8)
|
|
} else {
|
|
var extra uint = copylen - 2118
|
|
(*commands)[0] = uint32(63 | extra<<8)
|
|
}
|
|
|
|
*commands = (*commands)[1:]
|
|
}
|
|
|
|
func emitCopyLenLastDistance(copylen uint, commands *[]uint32) {
|
|
if copylen < 12 {
|
|
(*commands)[0] = uint32(copylen + 20)
|
|
*commands = (*commands)[1:]
|
|
} else if copylen < 72 {
|
|
var tail uint = copylen - 8
|
|
var nbits uint = uint(log2FloorNonZero(tail) - 1)
|
|
var prefix uint = tail >> nbits
|
|
var code uint = (nbits << 1) + prefix + 28
|
|
var extra uint = tail - (prefix << nbits)
|
|
(*commands)[0] = uint32(code | extra<<8)
|
|
*commands = (*commands)[1:]
|
|
} else if copylen < 136 {
|
|
var tail uint = copylen - 8
|
|
var code uint = (tail >> 5) + 54
|
|
var extra uint = tail & 31
|
|
(*commands)[0] = uint32(code | extra<<8)
|
|
*commands = (*commands)[1:]
|
|
(*commands)[0] = 64
|
|
*commands = (*commands)[1:]
|
|
} else if copylen < 2120 {
|
|
var tail uint = copylen - 72
|
|
var nbits uint = uint(log2FloorNonZero(tail))
|
|
var code uint = nbits + 52
|
|
var extra uint = tail - (uint(1) << nbits)
|
|
(*commands)[0] = uint32(code | extra<<8)
|
|
*commands = (*commands)[1:]
|
|
(*commands)[0] = 64
|
|
*commands = (*commands)[1:]
|
|
} else {
|
|
var extra uint = copylen - 2120
|
|
(*commands)[0] = uint32(63 | extra<<8)
|
|
*commands = (*commands)[1:]
|
|
(*commands)[0] = 64
|
|
*commands = (*commands)[1:]
|
|
}
|
|
}
|
|
|
|
func emitDistance(distance uint32, commands *[]uint32) {
|
|
var d uint32 = distance + 3
|
|
var nbits uint32 = log2FloorNonZero(uint(d)) - 1
|
|
var prefix uint32 = (d >> nbits) & 1
|
|
var offset uint32 = (2 + prefix) << nbits
|
|
var distcode uint32 = 2*(nbits-1) + prefix + 80
|
|
var extra uint32 = d - offset
|
|
(*commands)[0] = distcode | extra<<8
|
|
*commands = (*commands)[1:]
|
|
}
|
|
|
|
/* REQUIRES: len <= 1 << 24. */
|
|
func storeMetaBlockHeader(len uint, is_uncompressed bool, storage_ix *uint, storage []byte) {
|
|
var nibbles uint = 6
|
|
|
|
/* ISLAST */
|
|
writeBits(1, 0, storage_ix, storage)
|
|
|
|
if len <= 1<<16 {
|
|
nibbles = 4
|
|
} else if len <= 1<<20 {
|
|
nibbles = 5
|
|
}
|
|
|
|
writeBits(2, uint64(nibbles)-4, storage_ix, storage)
|
|
writeBits(nibbles*4, uint64(len)-1, storage_ix, storage)
|
|
|
|
/* ISUNCOMPRESSED */
|
|
writeSingleBit(is_uncompressed, storage_ix, storage)
|
|
}
|
|
|
|
func storeMetaBlockHeaderBW(len uint, is_uncompressed bool, bw *bitWriter) {
|
|
var nibbles uint = 6
|
|
|
|
/* ISLAST */
|
|
bw.writeBits(1, 0)
|
|
|
|
if len <= 1<<16 {
|
|
nibbles = 4
|
|
} else if len <= 1<<20 {
|
|
nibbles = 5
|
|
}
|
|
|
|
bw.writeBits(2, uint64(nibbles)-4)
|
|
bw.writeBits(nibbles*4, uint64(len)-1)
|
|
|
|
/* ISUNCOMPRESSED */
|
|
bw.writeSingleBit(is_uncompressed)
|
|
}
|
|
|
|
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) {
|
|
var ip int = 0
|
|
var shift uint = 64 - table_bits
|
|
var ip_end int = int(block_size)
|
|
var base_ip int = -cap(base_ip_ptr) + cap(input)
|
|
var next_emit int = 0
|
|
var last_distance int = -1
|
|
/* "ip" is the input pointer. */
|
|
|
|
const kInputMarginBytes uint = windowGap
|
|
|
|
/* "next_emit" is a pointer to the first byte that is not covered by a
|
|
previous copy. Bytes between "next_emit" and the start of the next copy or
|
|
the end of the input will be emitted as literal bytes. */
|
|
if block_size >= kInputMarginBytes {
|
|
var len_limit uint = brotli_min_size_t(block_size-min_match, input_size-kInputMarginBytes)
|
|
var ip_limit int = int(len_limit)
|
|
/* For the last block, we need to keep a 16 bytes margin so that we can be
|
|
sure that all distances are at most window size - 16.
|
|
For all other blocks, we only need to keep a margin of 5 bytes so that
|
|
we don't go over the block size with a copy. */
|
|
|
|
var next_hash uint32
|
|
ip++
|
|
for next_hash = hash1(input[ip:], shift, min_match); ; {
|
|
var skip uint32 = 32
|
|
var next_ip int = ip
|
|
/* Step 1: Scan forward in the input looking for a 6-byte-long match.
|
|
If we get close to exhausting the input then goto emit_remainder.
|
|
|
|
Heuristic match skipping: If 32 bytes are scanned with no matches
|
|
found, start looking only at every other byte. If 32 more bytes are
|
|
scanned, look at every third byte, etc.. When a match is found,
|
|
immediately go back to looking at every byte. This is a small loss
|
|
(~5% performance, ~0.1% density) for compressible data due to more
|
|
bookkeeping, but for non-compressible data (such as JPEG) it's a huge
|
|
win since the compressor quickly "realizes" the data is incompressible
|
|
and doesn't bother looking for matches everywhere.
|
|
|
|
The "skip" variable keeps track of how many bytes there are since the
|
|
last match; dividing it by 32 (ie. right-shifting by five) gives the
|
|
number of bytes to move ahead for each iteration. */
|
|
|
|
var candidate int
|
|
|
|
assert(next_emit < ip)
|
|
|
|
trawl:
|
|
for {
|
|
var hash uint32 = next_hash
|
|
var bytes_between_hash_lookups uint32 = skip >> 5
|
|
skip++
|
|
ip = next_ip
|
|
assert(hash == hash1(input[ip:], shift, min_match))
|
|
next_ip = int(uint32(ip) + bytes_between_hash_lookups)
|
|
if next_ip > ip_limit {
|
|
goto emit_remainder
|
|
}
|
|
|
|
next_hash = hash1(input[next_ip:], shift, min_match)
|
|
candidate = ip - last_distance
|
|
if isMatch1(input[ip:], base_ip_ptr[candidate-base_ip:], min_match) {
|
|
if candidate < ip {
|
|
table[hash] = int(ip - base_ip)
|
|
break
|
|
}
|
|
}
|
|
|
|
candidate = base_ip + table[hash]
|
|
assert(candidate >= base_ip)
|
|
assert(candidate < ip)
|
|
|
|
table[hash] = int(ip - base_ip)
|
|
if isMatch1(input[ip:], base_ip_ptr[candidate-base_ip:], min_match) {
|
|
break
|
|
}
|
|
}
|
|
|
|
/* Check copy distance. If candidate is not feasible, continue search.
|
|
Checking is done outside of hot loop to reduce overhead. */
|
|
if ip-candidate > maxDistance_compress_fragment {
|
|
goto trawl
|
|
}
|
|
|
|
/* Step 2: Emit the found match together with the literal bytes from
|
|
"next_emit", and then see if we can find a next match immediately
|
|
afterwards. Repeat until we find no match for the input
|
|
without emitting some literal bytes. */
|
|
{
|
|
var base int = ip
|
|
/* > 0 */
|
|
var matched uint = min_match + findMatchLengthWithLimit(base_ip_ptr[uint(candidate-base_ip)+min_match:], input[uint(ip)+min_match:], uint(ip_end-ip)-min_match)
|
|
var distance int = int(base - candidate)
|
|
/* We have a 6-byte match at ip, and we need to emit bytes in
|
|
[next_emit, ip). */
|
|
|
|
var insert int = int(base - next_emit)
|
|
ip += int(matched)
|
|
emitInsertLen(uint32(insert), commands)
|
|
copy(*literals, input[next_emit:][:uint(insert)])
|
|
*literals = (*literals)[insert:]
|
|
if distance == last_distance {
|
|
(*commands)[0] = 64
|
|
*commands = (*commands)[1:]
|
|
} else {
|
|
emitDistance(uint32(distance), commands)
|
|
last_distance = distance
|
|
}
|
|
|
|
emitCopyLenLastDistance(matched, 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 = binary.LittleEndian.Uint64(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 = binary.LittleEndian.Uint64(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 = binary.LittleEndian.Uint64(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 <= maxDistance_compress_fragment && isMatch1(input[ip:], base_ip_ptr[candidate-base_ip:], 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(base_ip_ptr[uint(candidate-base_ip)+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 = binary.LittleEndian.Uint64(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 = binary.LittleEndian.Uint64(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 = binary.LittleEndian.Uint64(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]]++
|
|
}
|
|
|
|
buildAndStoreHuffmanTreeFast(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)
|
|
writeBits(uint(cmd_depths[code]), uint64(cmd_bits[code]), storage_ix, storage)
|
|
writeBits(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]
|
|
writeBits(uint(lit_depths[lit]), uint64(lit_bits[lit]), storage_ix, storage)
|
|
literals = literals[1:]
|
|
}
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Acceptable loss for uncompressible speedup is 2% */
|
|
const minRatio = 0.98
|
|
|
|
const sampleRate = 43
|
|
|
|
func shouldCompress(input []byte, input_size uint, num_literals uint) bool {
|
|
var corpus_size float64 = float64(input_size)
|
|
if float64(num_literals) < minRatio*corpus_size {
|
|
return true
|
|
} else {
|
|
var literal_histo = [256]uint32{0}
|
|
var max_total_bit_cost float64 = corpus_size * 8 * minRatio / sampleRate
|
|
var i uint
|
|
for i = 0; i < input_size; i += sampleRate {
|
|
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) {
|
|
storeMetaBlockHeader(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 compressFragmentTwoPassImpl(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))
|
|
storeMetaBlockHeader(block_size, false, storage_ix, storage)
|
|
|
|
/* No block splits, no contexts. */
|
|
writeBits(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
|
|
}
|
|
}
|
|
|
|
/*
|
|
Compresses "input" string to the "*storage" buffer as one or more complete
|
|
|
|
meta-blocks, and updates the "*storage_ix" bit position.
|
|
|
|
If "is_last" is 1, emits an additional empty last meta-block.
|
|
|
|
REQUIRES: "input_size" is greater than zero, or "is_last" is 1.
|
|
REQUIRES: "input_size" is less or equal to maximal metablock size (1 << 24).
|
|
REQUIRES: "command_buf" and "literal_buf" point to at least
|
|
kCompressFragmentTwoPassBlockSize long arrays.
|
|
REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
|
|
REQUIRES: "table_size" is a power of two
|
|
OUTPUT: maximal copy distance <= |input_size|
|
|
OUTPUT: maximal copy distance <= BROTLI_MAX_BACKWARD_LIMIT(18)
|
|
*/
|
|
func compressFragmentTwoPass(input []byte, input_size uint, is_last bool, command_buf []uint32, literal_buf []byte, table []int, table_size uint, storage_ix *uint, storage []byte) {
|
|
var initial_storage_ix uint = *storage_ix
|
|
var table_bits uint = uint(log2FloorNonZero(table_size))
|
|
var min_match uint
|
|
if table_bits <= 15 {
|
|
min_match = 4
|
|
} else {
|
|
min_match = 6
|
|
}
|
|
compressFragmentTwoPassImpl(input, input_size, is_last, command_buf, literal_buf, table, table_bits, min_match, storage_ix, storage)
|
|
|
|
/* If output is larger than single uncompressed block, rewrite it. */
|
|
if *storage_ix-initial_storage_ix > 31+(input_size<<3) {
|
|
rewindBitPosition(initial_storage_ix, storage_ix, storage)
|
|
emitUncompressedMetaBlock(input, input_size, storage_ix, storage)
|
|
}
|
|
|
|
if is_last {
|
|
writeBits(1, 1, storage_ix, storage) /* islast */
|
|
writeBits(1, 1, storage_ix, storage) /* isempty */
|
|
*storage_ix = (*storage_ix + 7) &^ 7
|
|
}
|
|
}
|