diff options
Diffstat (limited to 'src/compress/flate/token.go')
| -rw-r--r-- | src/compress/flate/token.go | 102 |
1 files changed, 102 insertions, 0 deletions
diff --git a/src/compress/flate/token.go b/src/compress/flate/token.go new file mode 100644 index 000000000..4d4917687 --- /dev/null +++ b/src/compress/flate/token.go @@ -0,0 +1,102 @@ +// 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 + +const ( + // 2 bits: type 0 = literal 1=EOF 2=Match 3=Unused + // 8 bits: xlength = length - MIN_MATCH_LENGTH + // 22 bits xoffset = offset - MIN_OFFSET_SIZE, or literal + lengthShift = 22 + offsetMask = 1<<lengthShift - 1 + typeMask = 3 << 30 + literalType = 0 << 30 + matchType = 1 << 30 +) + +// The length code for length X (MIN_MATCH_LENGTH <= X <= MAX_MATCH_LENGTH) +// is lengthCodes[length - MIN_MATCH_LENGTH] +var lengthCodes = [...]uint32{ + 0, 1, 2, 3, 4, 5, 6, 7, 8, 8, + 9, 9, 10, 10, 11, 11, 12, 12, 12, 12, + 13, 13, 13, 13, 14, 14, 14, 14, 15, 15, + 15, 15, 16, 16, 16, 16, 16, 16, 16, 16, + 17, 17, 17, 17, 17, 17, 17, 17, 18, 18, + 18, 18, 18, 18, 18, 18, 19, 19, 19, 19, + 19, 19, 19, 19, 20, 20, 20, 20, 20, 20, + 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, + 21, 21, 21, 21, 21, 21, 21, 21, 21, 21, + 21, 21, 21, 21, 21, 21, 22, 22, 22, 22, + 22, 22, 22, 22, 22, 22, 22, 22, 22, 22, + 22, 22, 23, 23, 23, 23, 23, 23, 23, 23, + 23, 23, 23, 23, 23, 23, 23, 23, 24, 24, + 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, + 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, + 24, 24, 24, 24, 24, 24, 24, 24, 24, 24, + 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, + 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, + 25, 25, 25, 25, 25, 25, 25, 25, 25, 25, + 25, 25, 26, 26, 26, 26, 26, 26, 26, 26, + 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, + 26, 26, 26, 26, 26, 26, 26, 26, 26, 26, + 26, 26, 26, 26, 27, 27, 27, 27, 27, 27, + 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, + 27, 27, 27, 27, 27, 27, 27, 27, 27, 27, + 27, 27, 27, 27, 27, 28, +} + +var offsetCodes = [...]uint32{ + 0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, + 8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9, + 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, + 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, + 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, + 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, + 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, + 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, + 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, + 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, + 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, + 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, + 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, + 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, + 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, + 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, +} + +type token uint32 + +// Convert a literal into a literal token. +func literalToken(literal uint32) token { return token(literalType + literal) } + +// Convert a < xlength, xoffset > pair into a match token. +func matchToken(xlength uint32, xoffset uint32) token { + return token(matchType + xlength<<lengthShift + xoffset) +} + +// Returns the type of a token +func (t token) typ() uint32 { return uint32(t) & typeMask } + +// Returns the literal of a literal token +func (t token) literal() uint32 { return uint32(t - literalType) } + +// Returns the extra offset of a match token +func (t token) offset() uint32 { return uint32(t) & offsetMask } + +func (t token) length() uint32 { return uint32((t - matchType) >> lengthShift) } + +func lengthCode(len uint32) uint32 { return lengthCodes[len] } + +// Returns the offset code corresponding to a specific offset +func offsetCode(off uint32) uint32 { + const n = uint32(len(offsetCodes)) + switch { + case off < n: + return offsetCodes[off] + case off>>7 < n: + return offsetCodes[off>>7] + 14 + default: + return offsetCodes[off>>14] + 28 + } +} |