libgo/go/compress/flate/token.go

   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 type of a token
  79 func (t token) typ() uint32 { return uint32(t) & typeMask }
  80
  81 // Returns the literal of a literal token
  82 func (t token) literal() uint32 { return uint32(t - literalType) }
  83
  84 // Returns the extra offset of a match token
  85 func (t token) offset() uint32 { return uint32(t) & offsetMask }
  86
  87 func (t token) length() uint32 { return uint32((t - matchType) >> lengthShift) }
  88
  89 func lengthCode(len uint32) uint32 { return lengthCodes[len] }
  90
  91 // Returns the offset code corresponding to a specific offset
  92 func offsetCode(off uint32) uint32 {
  93         const n = uint32(len(offsetCodes))
  94         switch {
  95         case off < n:
  96                 return offsetCodes[off]
  97         case off>>7 < n:
  98                 return offsetCodes[off>>7] + 14
  99         default:
 100                 return offsetCodes[off>>14] + 28
 101         }
 102         panic("unreachable")
 103 }