token.mx raw
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