token.go

Documentation: compress/flate

		 1  // Copyright 2009 The Go Authors. All rights reserved.
		 2  // Use of this source code is governed by a BSD-style
		 3  // license that can be found in the LICENSE file.
		 4  
		 5  package flate
		 6  
		 7  const (
		 8  	// 2 bits:	 type	 0 = literal	1=EOF	2=Match	 3=Unused
		 9  	// 8 bits:	 xlength = length - MIN_MATCH_LENGTH
		10  	// 22 bits	 xoffset = offset - MIN_OFFSET_SIZE, or literal
		11  	lengthShift = 22
		12  	offsetMask	= 1<<lengthShift - 1
		13  	typeMask		= 3 << 30
		14  	literalType = 0 << 30
		15  	matchType	 = 1 << 30
		16  )
		17  
		18  // The length code for length X (MIN_MATCH_LENGTH <= X <= MAX_MATCH_LENGTH)
		19  // is lengthCodes[length - MIN_MATCH_LENGTH]
		20  var lengthCodes = [...]uint32{
		21  	0, 1, 2, 3, 4, 5, 6, 7, 8, 8,
		22  	9, 9, 10, 10, 11, 11, 12, 12, 12, 12,
		23  	13, 13, 13, 13, 14, 14, 14, 14, 15, 15,
		24  	15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
		25  	17, 17, 17, 17, 17, 17, 17, 17, 18, 18,
		26  	18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
		27  	19, 19, 19, 19, 20, 20, 20, 20, 20, 20,
		28  	20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
		29  	21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
		30  	21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
		31  	22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
		32  	22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
		33  	23, 23, 23, 23, 23, 23, 23, 23, 24, 24,
		34  	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
		35  	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
		36  	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
		37  	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
		38  	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
		39  	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
		40  	25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
		41  	26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
		42  	26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
		43  	26, 26, 26, 26, 27, 27, 27, 27, 27, 27,
		44  	27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
		45  	27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
		46  	27, 27, 27, 27, 27, 28,
		47  }
		48  
		49  var offsetCodes = [...]uint32{
		50  	0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7,
		51  	8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9,
		52  	10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
		53  	11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
		54  	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
		55  	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
		56  	13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
		57  	13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
		58  	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
		59  	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
		60  	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
		61  	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
		62  	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
		63  	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
		64  	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
		65  	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
		66  }
		67  
		68  type token uint32
		69  
		70  // Convert a literal into a literal token.
		71  func literalToken(literal uint32) token { return token(literalType + literal) }
		72  
		73  // Convert a < xlength, xoffset > pair into a match token.
		74  func matchToken(xlength uint32, xoffset uint32) token {
		75  	return token(matchType + xlength<<lengthShift + xoffset)
		76  }
		77  
		78  // Returns the literal of a literal token
		79  func (t token) literal() uint32 { return uint32(t - literalType) }
		80  
		81  // Returns the extra offset of a match token
		82  func (t token) offset() uint32 { return uint32(t) & offsetMask }
		83  
		84  func (t token) length() uint32 { return uint32((t - matchType) >> lengthShift) }
		85  
		86  func lengthCode(len uint32) uint32 { return lengthCodes[len] }
		87  
		88  // Returns the offset code corresponding to a specific offset
		89  func offsetCode(off uint32) uint32 {
		90  	if off < uint32(len(offsetCodes)) {
		91  		return offsetCodes[off]
		92  	}
		93  	if off>>7 < uint32(len(offsetCodes)) {
		94  		return offsetCodes[off>>7] + 14
		95  	}
		96  	return offsetCodes[off>>14] + 28
		97  }
		98
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