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@@ -7,19 +7,19 @@ package flate
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// dictDecoder implements the LZ77 sliding dictionary as used in decompression.
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// LZ77 decompresses data through sequences of two forms of commands:
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//
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// * Literal insertions: Runs of one or more symbols are inserted into the data
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// stream as is. This is accomplished through the writeByte method for a
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// single symbol, or combinations of writeSlice/writeMark for multiple symbols.
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// Any valid stream must start with a literal insertion if no preset dictionary
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// is used.
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// - Literal insertions: Runs of one or more symbols are inserted into the data
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// stream as is. This is accomplished through the writeByte method for a
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// single symbol, or combinations of writeSlice/writeMark for multiple symbols.
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// Any valid stream must start with a literal insertion if no preset dictionary
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// is used.
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//
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// * Backward copies: Runs of one or more symbols are copied from previously
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// emitted data. Backward copies come as the tuple (dist, length) where dist
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// determines how far back in the stream to copy from and length determines how
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// many bytes to copy. Note that it is valid for the length to be greater than
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// the distance. Since LZ77 uses forward copies, that situation is used to
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// perform a form of run-length encoding on repeated runs of symbols.
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// The writeCopy and tryWriteCopy are used to implement this command.
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// - Backward copies: Runs of one or more symbols are copied from previously
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// emitted data. Backward copies come as the tuple (dist, length) where dist
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// determines how far back in the stream to copy from and length determines how
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// many bytes to copy. Note that it is valid for the length to be greater than
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// the distance. Since LZ77 uses forward copies, that situation is used to
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// perform a form of run-length encoding on repeated runs of symbols.
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// The writeCopy and tryWriteCopy are used to implement this command.
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//
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// For performance reasons, this implementation performs little to no sanity
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// checks about the arguments. As such, the invariants documented for each
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@@ -194,9 +194,9 @@ func (w *huffmanBitWriter) writeBytes(bytes []byte) {
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// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
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// information. Code badCode is an end marker
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//
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// numLiterals The number of literals in literalEncoding
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// numOffsets The number of offsets in offsetEncoding
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// litenc, offenc The literal and offset encoder to use
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// numLiterals The number of literals in literalEncoding
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// numOffsets The number of offsets in offsetEncoding
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// litenc, offenc The literal and offset encoder to use
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func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litEnc, offEnc *huffmanEncoder) {
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for i := range w.codegenFreq {
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w.codegenFreq[i] = 0
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@@ -353,9 +353,9 @@ func (w *huffmanBitWriter) writeCode(c hcode) {
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// Write the header of a dynamic Huffman block to the output stream.
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//
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// numLiterals The number of literals specified in codegen
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// numOffsets The number of offsets specified in codegen
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// numCodegens The number of codegens used in codegen
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// numLiterals The number of literals specified in codegen
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// numOffsets The number of offsets specified in codegen
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// numCodegens The number of codegens used in codegen
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func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
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if w.err != nil {
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return
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@@ -124,13 +124,18 @@ const maxBitsLimit = 16
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// The cases of 0, 1, and 2 literals are handled by special case code.
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//
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// list An array of the literals with non-zero frequencies
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// and their associated frequencies. The array is in order of increasing
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// frequency, and has as its last element a special element with frequency
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// MaxInt32
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//
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// and their associated frequencies. The array is in order of increasing
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// frequency, and has as its last element a special element with frequency
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// MaxInt32
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//
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// maxBits The maximum number of bits that should be used to encode any literal.
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// Must be less than 16.
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//
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// Must be less than 16.
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//
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// return An integer array in which array[i] indicates the number of literals
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// that should be encoded in i bits.
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//
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// that should be encoded in i bits.
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func (h *huffmanEncoder) bitCounts(list []literalNode, maxBits int32) []int32 {
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if maxBits >= maxBitsLimit {
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panic("flate: maxBits too large")
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