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Diffstat (limited to 'vendor/github.com/klauspost/compress/flate/huffman_code.go')
| -rw-r--r-- | vendor/github.com/klauspost/compress/flate/huffman_code.go | 344 |
1 files changed, 0 insertions, 344 deletions
diff --git a/vendor/github.com/klauspost/compress/flate/huffman_code.go b/vendor/github.com/klauspost/compress/flate/huffman_code.go deleted file mode 100644 index bdcbd823..00000000 --- a/vendor/github.com/klauspost/compress/flate/huffman_code.go +++ /dev/null @@ -1,344 +0,0 @@ -// Copyright 2009 The Go Authors. All rights reserved. -// Use of this source code is governed by a BSD-style -// license that can be found in the LICENSE file. - -package flate - -import ( - "math" - "sort" -) - -// hcode is a huffman code with a bit code and bit length. -type hcode struct { - code, len uint16 -} - -type huffmanEncoder struct { - codes []hcode - freqcache []literalNode - bitCount [17]int32 - lns byLiteral // stored to avoid repeated allocation in generate - lfs byFreq // stored to avoid repeated allocation in generate -} - -type literalNode struct { - literal uint16 - freq int32 -} - -// A levelInfo describes the state of the constructed tree for a given depth. -type levelInfo struct { - // Our level. for better printing - level int32 - - // The frequency of the last node at this level - lastFreq int32 - - // The frequency of the next character to add to this level - nextCharFreq int32 - - // The frequency of the next pair (from level below) to add to this level. - // Only valid if the "needed" value of the next lower level is 0. - nextPairFreq int32 - - // The number of chains remaining to generate for this level before moving - // up to the next level - needed int32 -} - -// set sets the code and length of an hcode. -func (h *hcode) set(code uint16, length uint16) { - h.len = length - h.code = code -} - -func maxNode() literalNode { return literalNode{math.MaxUint16, math.MaxInt32} } - -func newHuffmanEncoder(size int) *huffmanEncoder { - return &huffmanEncoder{codes: make([]hcode, size)} -} - -// Generates a HuffmanCode corresponding to the fixed literal table -func generateFixedLiteralEncoding() *huffmanEncoder { - h := newHuffmanEncoder(maxNumLit) - codes := h.codes - var ch uint16 - for ch = 0; ch < maxNumLit; ch++ { - var bits uint16 - var size uint16 - switch { - case ch < 144: - // size 8, 000110000 .. 10111111 - bits = ch + 48 - size = 8 - break - case ch < 256: - // size 9, 110010000 .. 111111111 - bits = ch + 400 - 144 - size = 9 - break - case ch < 280: - // size 7, 0000000 .. 0010111 - bits = ch - 256 - size = 7 - break - default: - // size 8, 11000000 .. 11000111 - bits = ch + 192 - 280 - size = 8 - } - codes[ch] = hcode{code: reverseBits(bits, byte(size)), len: size} - } - return h -} - -func generateFixedOffsetEncoding() *huffmanEncoder { - h := newHuffmanEncoder(30) - codes := h.codes - for ch := range codes { - codes[ch] = hcode{code: reverseBits(uint16(ch), 5), len: 5} - } - return h -} - -var fixedLiteralEncoding *huffmanEncoder = generateFixedLiteralEncoding() -var fixedOffsetEncoding *huffmanEncoder = generateFixedOffsetEncoding() - -func (h *huffmanEncoder) bitLength(freq []int32) int { - var total int - for i, f := range freq { - if f != 0 { - total += int(f) * int(h.codes[i].len) - } - } - return total -} - -const maxBitsLimit = 16 - -// Return the number of literals assigned to each bit size in the Huffman encoding -// -// This method is only called when list.length >= 3 -// The cases of 0, 1, and 2 literals are handled by special case code. -// -// list An array of the literals with non-zero frequencies -// and their associated frequencies. The array is in order of increasing -// frequency, and has as its last element a special element with frequency -// MaxInt32 -// maxBits The maximum number of bits that should be used to encode any literal. -// Must be less than 16. -// return An integer array in which array[i] indicates the number of literals -// that should be encoded in i bits. -func (h *huffmanEncoder) bitCounts(list []literalNode, maxBits int32) []int32 { - if maxBits >= maxBitsLimit { - panic("flate: maxBits too large") - } - n := int32(len(list)) - list = list[0 : n+1] - list[n] = maxNode() - - // The tree can't have greater depth than n - 1, no matter what. This - // saves a little bit of work in some small cases - if maxBits > n-1 { - maxBits = n - 1 - } - - // Create information about each of the levels. - // A bogus "Level 0" whose sole purpose is so that - // level1.prev.needed==0. This makes level1.nextPairFreq - // be a legitimate value that never gets chosen. - var levels [maxBitsLimit]levelInfo - // leafCounts[i] counts the number of literals at the left - // of ancestors of the rightmost node at level i. - // leafCounts[i][j] is the number of literals at the left - // of the level j ancestor. - var leafCounts [maxBitsLimit][maxBitsLimit]int32 - - for level := int32(1); level <= maxBits; level++ { - // For every level, the first two items are the first two characters. - // We initialize the levels as if we had already figured this out. - levels[level] = levelInfo{ - level: level, - lastFreq: list[1].freq, - nextCharFreq: list[2].freq, - nextPairFreq: list[0].freq + list[1].freq, - } - leafCounts[level][level] = 2 - if level == 1 { - levels[level].nextPairFreq = math.MaxInt32 - } - } - - // We need a total of 2*n - 2 items at top level and have already generated 2. - levels[maxBits].needed = 2*n - 4 - - level := maxBits - for { - l := &levels[level] - if l.nextPairFreq == math.MaxInt32 && l.nextCharFreq == math.MaxInt32 { - // We've run out of both leafs and pairs. - // End all calculations for this level. - // To make sure we never come back to this level or any lower level, - // set nextPairFreq impossibly large. - l.needed = 0 - levels[level+1].nextPairFreq = math.MaxInt32 - level++ - continue - } - - prevFreq := l.lastFreq - if l.nextCharFreq < l.nextPairFreq { - // The next item on this row is a leaf node. - n := leafCounts[level][level] + 1 - l.lastFreq = l.nextCharFreq - // Lower leafCounts are the same of the previous node. - leafCounts[level][level] = n - l.nextCharFreq = list[n].freq - } else { - // The next item on this row is a pair from the previous row. - // nextPairFreq isn't valid until we generate two - // more values in the level below - l.lastFreq = l.nextPairFreq - // Take leaf counts from the lower level, except counts[level] remains the same. - copy(leafCounts[level][:level], leafCounts[level-1][:level]) - levels[l.level-1].needed = 2 - } - - if l.needed--; l.needed == 0 { - // We've done everything we need to do for this level. - // Continue calculating one level up. Fill in nextPairFreq - // of that level with the sum of the two nodes we've just calculated on - // this level. - if l.level == maxBits { - // All done! - break - } - levels[l.level+1].nextPairFreq = prevFreq + l.lastFreq - level++ - } else { - // If we stole from below, move down temporarily to replenish it. - for levels[level-1].needed > 0 { - level-- - } - } - } - - // Somethings is wrong if at the end, the top level is null or hasn't used - // all of the leaves. - if leafCounts[maxBits][maxBits] != n { - panic("leafCounts[maxBits][maxBits] != n") - } - - bitCount := h.bitCount[:maxBits+1] - bits := 1 - counts := &leafCounts[maxBits] - for level := maxBits; level > 0; level-- { - // chain.leafCount gives the number of literals requiring at least "bits" - // bits to encode. - bitCount[bits] = counts[level] - counts[level-1] - bits++ - } - return bitCount -} - -// Look at the leaves and assign them a bit count and an encoding as specified -// in RFC 1951 3.2.2 -func (h *huffmanEncoder) assignEncodingAndSize(bitCount []int32, list []literalNode) { - code := uint16(0) - for n, bits := range bitCount { - code <<= 1 - if n == 0 || bits == 0 { - continue - } - // The literals list[len(list)-bits] .. list[len(list)-bits] - // are encoded using "bits" bits, and get the values - // code, code + 1, .... The code values are - // assigned in literal order (not frequency order). - chunk := list[len(list)-int(bits):] - - h.lns.sort(chunk) - for _, node := range chunk { - h.codes[node.literal] = hcode{code: reverseBits(code, uint8(n)), len: uint16(n)} - code++ - } - list = list[0 : len(list)-int(bits)] - } -} - -// Update this Huffman Code object to be the minimum code for the specified frequency count. -// -// freq An array of frequencies, in which frequency[i] gives the frequency of literal i. -// maxBits The maximum number of bits to use for any literal. -func (h *huffmanEncoder) generate(freq []int32, maxBits int32) { - if h.freqcache == nil { - // Allocate a reusable buffer with the longest possible frequency table. - // Possible lengths are codegenCodeCount, offsetCodeCount and maxNumLit. - // The largest of these is maxNumLit, so we allocate for that case. - h.freqcache = make([]literalNode, maxNumLit+1) - } - list := h.freqcache[:len(freq)+1] - // Number of non-zero literals - count := 0 - // Set list to be the set of all non-zero literals and their frequencies - for i, f := range freq { - if f != 0 { - list[count] = literalNode{uint16(i), f} - count++ - } else { - list[count] = literalNode{} - h.codes[i].len = 0 - } - } - list[len(freq)] = literalNode{} - - list = list[:count] - if count <= 2 { - // Handle the small cases here, because they are awkward for the general case code. With - // two or fewer literals, everything has bit length 1. - for i, node := range list { - // "list" is in order of increasing literal value. - h.codes[node.literal].set(uint16(i), 1) - } - return - } - h.lfs.sort(list) - - // Get the number of literals for each bit count - bitCount := h.bitCounts(list, maxBits) - // And do the assignment - h.assignEncodingAndSize(bitCount, list) -} - -type byLiteral []literalNode - -func (s *byLiteral) sort(a []literalNode) { - *s = byLiteral(a) - sort.Sort(s) -} - -func (s byLiteral) Len() int { return len(s) } - -func (s byLiteral) Less(i, j int) bool { - return s[i].literal < s[j].literal -} - -func (s byLiteral) Swap(i, j int) { s[i], s[j] = s[j], s[i] } - -type byFreq []literalNode - -func (s *byFreq) sort(a []literalNode) { - *s = byFreq(a) - sort.Sort(s) -} - -func (s byFreq) Len() int { return len(s) } - -func (s byFreq) Less(i, j int) bool { - if s[i].freq == s[j].freq { - return s[i].literal < s[j].literal - } - return s[i].freq < s[j].freq -} - -func (s byFreq) Swap(i, j int) { s[i], s[j] = s[j], s[i] } |