From 500caaeda74dd9c660279036293f4b2997cf0b03 Mon Sep 17 00:00:00 2001 From: Dimitri Sokolyuk Date: Sat, 9 Sep 2017 09:42:37 +0200 Subject: Add vendor --- vendor/golang.org/x/image/vp8/partition.go | 129 +++++++++++++++++++++++++++++ 1 file changed, 129 insertions(+) create mode 100644 vendor/golang.org/x/image/vp8/partition.go (limited to 'vendor/golang.org/x/image/vp8/partition.go') diff --git a/vendor/golang.org/x/image/vp8/partition.go b/vendor/golang.org/x/image/vp8/partition.go new file mode 100644 index 0000000..72288bd --- /dev/null +++ b/vendor/golang.org/x/image/vp8/partition.go @@ -0,0 +1,129 @@ +// Copyright 2011 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 vp8 + +// Each VP8 frame consists of between 2 and 9 bitstream partitions. +// Each partition is byte-aligned and is independently arithmetic-encoded. +// +// This file implements decoding a partition's bitstream, as specified in +// chapter 7. The implementation follows libwebp's approach instead of the +// specification's reference C implementation. For example, we use a look-up +// table instead of a for loop to recalibrate the encoded range. + +var ( + lutShift = [127]uint8{ + 7, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 4, 4, 4, 4, + 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, + 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, + 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, + 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, + } + lutRangeM1 = [127]uint8{ + 127, + 127, 191, + 127, 159, 191, 223, + 127, 143, 159, 175, 191, 207, 223, 239, + 127, 135, 143, 151, 159, 167, 175, 183, 191, 199, 207, 215, 223, 231, 239, 247, + 127, 131, 135, 139, 143, 147, 151, 155, 159, 163, 167, 171, 175, 179, 183, 187, + 191, 195, 199, 203, 207, 211, 215, 219, 223, 227, 231, 235, 239, 243, 247, 251, + 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149, 151, 153, 155, 157, + 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179, 181, 183, 185, 187, 189, + 191, 193, 195, 197, 199, 201, 203, 205, 207, 209, 211, 213, 215, 217, 219, 221, + 223, 225, 227, 229, 231, 233, 235, 237, 239, 241, 243, 245, 247, 249, 251, 253, + } +) + +// uniformProb represents a 50% probability that the next bit is 0. +const uniformProb = 128 + +// partition holds arithmetic-coded bits. +type partition struct { + // buf is the input bytes. + buf []byte + // r is how many of buf's bytes have been consumed. + r int + // rangeM1 is range minus 1, where range is in the arithmetic coding sense, + // not the Go language sense. + rangeM1 uint32 + // bits and nBits hold those bits shifted out of buf but not yet consumed. + bits uint32 + nBits uint8 + // unexpectedEOF tells whether we tried to read past buf. + unexpectedEOF bool +} + +// init initializes the partition. +func (p *partition) init(buf []byte) { + p.buf = buf + p.r = 0 + p.rangeM1 = 254 + p.bits = 0 + p.nBits = 0 + p.unexpectedEOF = false +} + +// readBit returns the next bit. +func (p *partition) readBit(prob uint8) bool { + if p.nBits < 8 { + if p.r >= len(p.buf) { + p.unexpectedEOF = true + return false + } + // Expression split for 386 compiler. + x := uint32(p.buf[p.r]) + p.bits |= x << (8 - p.nBits) + p.r++ + p.nBits += 8 + } + split := (p.rangeM1*uint32(prob))>>8 + 1 + bit := p.bits >= split<<8 + if bit { + p.rangeM1 -= split + p.bits -= split << 8 + } else { + p.rangeM1 = split - 1 + } + if p.rangeM1 < 127 { + shift := lutShift[p.rangeM1] + p.rangeM1 = uint32(lutRangeM1[p.rangeM1]) + p.bits <<= shift + p.nBits -= shift + } + return bit +} + +// readUint returns the next n-bit unsigned integer. +func (p *partition) readUint(prob, n uint8) uint32 { + var u uint32 + for n > 0 { + n-- + if p.readBit(prob) { + u |= 1 << n + } + } + return u +} + +// readInt returns the next n-bit signed integer. +func (p *partition) readInt(prob, n uint8) int32 { + u := p.readUint(prob, n) + b := p.readBit(prob) + if b { + return -int32(u) + } + return int32(u) +} + +// readOptionalInt returns the next n-bit signed integer in an encoding +// where the likely result is zero. +func (p *partition) readOptionalInt(prob, n uint8) int32 { + if !p.readBit(prob) { + return 0 + } + return p.readInt(prob, n) +} -- cgit v1.2.3