// Copyright 2014 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 vp8l import ( "io" ) // reverseBits reverses the bits in a byte. var reverseBits = [256]uint8{ 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0, 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8, 0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4, 0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc, 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa, 0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6, 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1, 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9, 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd, 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3, 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb, 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7, 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff, } // hNode is a node in a Huffman tree. type hNode struct { // symbol is the symbol held by this node. symbol uint32 // children, if positive, is the hTree.nodes index of the first of // this node's two children. Zero means an uninitialized node, // and -1 means a leaf node. children int32 } const leafNode = -1 // lutSize is the log-2 size of an hTree's look-up table. const lutSize, lutMask = 7, 1<<7 - 1 // hTree is a Huffman tree. type hTree struct { // nodes are the nodes of the Huffman tree. During construction, // len(nodes) grows from 1 up to cap(nodes) by steps of two. // After construction, len(nodes) == cap(nodes), and both equal // 2*theNumberOfSymbols - 1. nodes []hNode // lut is a look-up table for walking the nodes. The x in lut[x] is // the next lutSize bits in the bit-stream. The low 8 bits of lut[x] // equals 1 plus the number of bits in the next code, or 0 if the // next code requires more than lutSize bits. The high 24 bits are: // - the symbol, if the code requires lutSize or fewer bits, or // - the hTree.nodes index to start the tree traversal from, if // the next code requires more than lutSize bits. lut [1 << lutSize]uint32 } // insert inserts into the hTree a symbol whose encoding is the least // significant codeLength bits of code. func (h *hTree) insert(symbol uint32, code uint32, codeLength uint32) error { if symbol > 0xffff || codeLength > 0xfe { return errInvalidHuffmanTree } baseCode := uint32(0) if codeLength > lutSize { baseCode = uint32(reverseBits[(code>>(codeLength-lutSize))&0xff]) >> (8 - lutSize) } else { baseCode = uint32(reverseBits[code&0xff]) >> (8 - codeLength) for i := 0; i < 1<<(lutSize-codeLength); i++ { h.lut[baseCode|uint32(i)<<codeLength] = symbol<<8 | (codeLength + 1) } } n := uint32(0) for jump := lutSize; codeLength > 0; { codeLength-- if int(n) > len(h.nodes) { return errInvalidHuffmanTree } switch h.nodes[n].children { case leafNode: return errInvalidHuffmanTree case 0: if len(h.nodes) == cap(h.nodes) { return errInvalidHuffmanTree } // Create two empty child nodes. h.nodes[n].children = int32(len(h.nodes)) h.nodes = h.nodes[:len(h.nodes)+2] } n = uint32(h.nodes[n].children) + 1&(code>>codeLength) jump-- if jump == 0 && h.lut[baseCode] == 0 { h.lut[baseCode] = n << 8 } } switch h.nodes[n].children { case leafNode: // No-op. case 0: // Turn the uninitialized node into a leaf. h.nodes[n].children = leafNode default: return errInvalidHuffmanTree } h.nodes[n].symbol = symbol return nil } // codeLengthsToCodes returns the canonical Huffman codes implied by the // sequence of code lengths. func codeLengthsToCodes(codeLengths []uint32) ([]uint32, error) { maxCodeLength := uint32(0) for _, cl := range codeLengths { if maxCodeLength < cl { maxCodeLength = cl } } const maxAllowedCodeLength = 15 if len(codeLengths) == 0 || maxCodeLength > maxAllowedCodeLength { return nil, errInvalidHuffmanTree } histogram := [maxAllowedCodeLength + 1]uint32{} for _, cl := range codeLengths { histogram[cl]++ } currCode, nextCodes := uint32(0), [maxAllowedCodeLength + 1]uint32{} for cl := 1; cl < len(nextCodes); cl++ { currCode = (currCode + histogram[cl-1]) << 1 nextCodes[cl] = currCode } codes := make([]uint32, len(codeLengths)) for symbol, cl := range codeLengths { if cl > 0 { codes[symbol] = nextCodes[cl] nextCodes[cl]++ } } return codes, nil } // build builds a canonical Huffman tree from the given code lengths. func (h *hTree) build(codeLengths []uint32) error { // Calculate the number of symbols. var nSymbols, lastSymbol uint32 for symbol, cl := range codeLengths { if cl != 0 { nSymbols++ lastSymbol = uint32(symbol) } } if nSymbols == 0 { return errInvalidHuffmanTree } h.nodes = make([]hNode, 1, 2*nSymbols-1) // Handle the trivial case. if nSymbols == 1 { if len(codeLengths) <= int(lastSymbol) { return errInvalidHuffmanTree } return h.insert(lastSymbol, 0, 0) } // Handle the non-trivial case. codes, err := codeLengthsToCodes(codeLengths) if err != nil { return err } for symbol, cl := range codeLengths { if cl > 0 { if err := h.insert(uint32(symbol), codes[symbol], cl); err != nil { return err } } } return nil } // buildSimple builds a Huffman tree with 1 or 2 symbols. func (h *hTree) buildSimple(nSymbols uint32, symbols [2]uint32, alphabetSize uint32) error { h.nodes = make([]hNode, 1, 2*nSymbols-1) for i := uint32(0); i < nSymbols; i++ { if symbols[i] >= alphabetSize { return errInvalidHuffmanTree } if err := h.insert(symbols[i], i, nSymbols-1); err != nil { return err } } return nil } // next returns the next Huffman-encoded symbol from the bit-stream d. func (h *hTree) next(d *decoder) (uint32, error) { var n uint32 // Read enough bits so that we can use the look-up table. if d.nBits < lutSize { c, err := d.r.ReadByte() if err != nil { if err == io.EOF { // There are no more bytes of data, but we may still be able // to read the next symbol out of the previously read bits. goto slowPath } return 0, err } d.bits |= uint32(c) << d.nBits d.nBits += 8 } // Use the look-up table. n = h.lut[d.bits&lutMask] if b := n & 0xff; b != 0 { b-- d.bits >>= b d.nBits -= b return n >> 8, nil } n >>= 8 d.bits >>= lutSize d.nBits -= lutSize slowPath: for h.nodes[n].children != leafNode { if d.nBits == 0 { c, err := d.r.ReadByte() if err != nil { if err == io.EOF { err = io.ErrUnexpectedEOF } return 0, err } d.bits = uint32(c) d.nBits = 8 } n = uint32(h.nodes[n].children) + 1&d.bits d.bits >>= 1 d.nBits-- } return h.nodes[n].symbol, nil }