diff options
Diffstat (limited to 'Godeps/_workspace/src/github.com/golang/snappy/encode.go')
| -rw-r--r-- | Godeps/_workspace/src/github.com/golang/snappy/encode.go | 356 |
1 files changed, 0 insertions, 356 deletions
diff --git a/Godeps/_workspace/src/github.com/golang/snappy/encode.go b/Godeps/_workspace/src/github.com/golang/snappy/encode.go deleted file mode 100644 index 834e3b06a..000000000 --- a/Godeps/_workspace/src/github.com/golang/snappy/encode.go +++ /dev/null @@ -1,356 +0,0 @@ -// Copyright 2011 The Snappy-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 snappy - -import ( - "encoding/binary" - "errors" - "io" -) - -// We limit how far copy back-references can go, the same as the C++ code. -const maxOffset = 1 << 15 - -// emitLiteral writes a literal chunk and returns the number of bytes written. -func emitLiteral(dst, lit []byte) int { - i, n := 0, uint(len(lit)-1) - switch { - case n < 60: - dst[0] = uint8(n)<<2 | tagLiteral - i = 1 - case n < 1<<8: - dst[0] = 60<<2 | tagLiteral - dst[1] = uint8(n) - i = 2 - case n < 1<<16: - dst[0] = 61<<2 | tagLiteral - dst[1] = uint8(n) - dst[2] = uint8(n >> 8) - i = 3 - case n < 1<<24: - dst[0] = 62<<2 | tagLiteral - dst[1] = uint8(n) - dst[2] = uint8(n >> 8) - dst[3] = uint8(n >> 16) - i = 4 - case int64(n) < 1<<32: - dst[0] = 63<<2 | tagLiteral - dst[1] = uint8(n) - dst[2] = uint8(n >> 8) - dst[3] = uint8(n >> 16) - dst[4] = uint8(n >> 24) - i = 5 - default: - panic("snappy: source buffer is too long") - } - if copy(dst[i:], lit) != len(lit) { - panic("snappy: destination buffer is too short") - } - return i + len(lit) -} - -// emitCopy writes a copy chunk and returns the number of bytes written. -func emitCopy(dst []byte, offset, length int) int { - i := 0 - for length > 0 { - x := length - 4 - if 0 <= x && x < 1<<3 && offset < 1<<11 { - dst[i+0] = uint8(offset>>8)&0x07<<5 | uint8(x)<<2 | tagCopy1 - dst[i+1] = uint8(offset) - i += 2 - break - } - - x = length - if x > 1<<6 { - x = 1 << 6 - } - dst[i+0] = uint8(x-1)<<2 | tagCopy2 - dst[i+1] = uint8(offset) - dst[i+2] = uint8(offset >> 8) - i += 3 - length -= x - } - return i -} - -// Encode returns the encoded form of src. The returned slice may be a sub- -// slice of dst if dst was large enough to hold the entire encoded block. -// Otherwise, a newly allocated slice will be returned. -// It is valid to pass a nil dst. -func Encode(dst, src []byte) []byte { - if n := MaxEncodedLen(len(src)); len(dst) < n { - dst = make([]byte, n) - } - - // The block starts with the varint-encoded length of the decompressed bytes. - d := binary.PutUvarint(dst, uint64(len(src))) - - // Return early if src is short. - if len(src) <= 4 { - if len(src) != 0 { - d += emitLiteral(dst[d:], src) - } - return dst[:d] - } - - // Initialize the hash table. Its size ranges from 1<<8 to 1<<14 inclusive. - const maxTableSize = 1 << 14 - shift, tableSize := uint(32-8), 1<<8 - for tableSize < maxTableSize && tableSize < len(src) { - shift-- - tableSize *= 2 - } - var table [maxTableSize]int - - // Iterate over the source bytes. - var ( - s int // The iterator position. - t int // The last position with the same hash as s. - lit int // The start position of any pending literal bytes. - ) - for s+3 < len(src) { - // Update the hash table. - b0, b1, b2, b3 := src[s], src[s+1], src[s+2], src[s+3] - h := uint32(b0) | uint32(b1)<<8 | uint32(b2)<<16 | uint32(b3)<<24 - p := &table[(h*0x1e35a7bd)>>shift] - // We need to to store values in [-1, inf) in table. To save - // some initialization time, (re)use the table's zero value - // and shift the values against this zero: add 1 on writes, - // subtract 1 on reads. - t, *p = *p-1, s+1 - // If t is invalid or src[s:s+4] differs from src[t:t+4], accumulate a literal byte. - if t < 0 || s-t >= maxOffset || b0 != src[t] || b1 != src[t+1] || b2 != src[t+2] || b3 != src[t+3] { - // Skip multiple bytes if the last match was >= 32 bytes prior. - s += 1 + (s-lit)>>5 - continue - } - // Otherwise, we have a match. First, emit any pending literal bytes. - if lit != s { - d += emitLiteral(dst[d:], src[lit:s]) - } - // Extend the match to be as long as possible. - s0 := s - s, t = s+4, t+4 - for s < len(src) && src[s] == src[t] { - s++ - t++ - } - // Emit the copied bytes. - d += emitCopy(dst[d:], s-t, s-s0) - lit = s - } - - // Emit any final pending literal bytes and return. - if lit != len(src) { - d += emitLiteral(dst[d:], src[lit:]) - } - return dst[:d] -} - -// MaxEncodedLen returns the maximum length of a snappy block, given its -// uncompressed length. -func MaxEncodedLen(srcLen int) int { - // Compressed data can be defined as: - // compressed := item* literal* - // item := literal* copy - // - // The trailing literal sequence has a space blowup of at most 62/60 - // since a literal of length 60 needs one tag byte + one extra byte - // for length information. - // - // Item blowup is trickier to measure. Suppose the "copy" op copies - // 4 bytes of data. Because of a special check in the encoding code, - // we produce a 4-byte copy only if the offset is < 65536. Therefore - // the copy op takes 3 bytes to encode, and this type of item leads - // to at most the 62/60 blowup for representing literals. - // - // Suppose the "copy" op copies 5 bytes of data. If the offset is big - // enough, it will take 5 bytes to encode the copy op. Therefore the - // worst case here is a one-byte literal followed by a five-byte copy. - // That is, 6 bytes of input turn into 7 bytes of "compressed" data. - // - // This last factor dominates the blowup, so the final estimate is: - return 32 + srcLen + srcLen/6 -} - -var errClosed = errors.New("snappy: Writer is closed") - -// NewWriter returns a new Writer that compresses to w. -// -// The Writer returned does not buffer writes. There is no need to Flush or -// Close such a Writer. -// -// Deprecated: the Writer returned is not suitable for many small writes, only -// for few large writes. Use NewBufferedWriter instead, which is efficient -// regardless of the frequency and shape of the writes, and remember to Close -// that Writer when done. -func NewWriter(w io.Writer) *Writer { - return &Writer{ - w: w, - obuf: make([]byte, obufLen), - } -} - -// NewBufferedWriter returns a new Writer that compresses to w, using the -// framing format described at -// https://github.com/google/snappy/blob/master/framing_format.txt -// -// The Writer returned buffers writes. Users must call Close to guarantee all -// data has been forwarded to the underlying io.Writer. They may also call -// Flush zero or more times before calling Close. -func NewBufferedWriter(w io.Writer) *Writer { - return &Writer{ - w: w, - ibuf: make([]byte, 0, maxUncompressedChunkLen), - obuf: make([]byte, obufLen), - } -} - -// Writer is an io.Writer than can write Snappy-compressed bytes. -type Writer struct { - w io.Writer - err error - - // ibuf is a buffer for the incoming (uncompressed) bytes. - // - // Its use is optional. For backwards compatibility, Writers created by the - // NewWriter function have ibuf == nil, do not buffer incoming bytes, and - // therefore do not need to be Flush'ed or Close'd. - ibuf []byte - - // obuf is a buffer for the outgoing (compressed) bytes. - obuf []byte - - // wroteStreamHeader is whether we have written the stream header. - wroteStreamHeader bool -} - -// Reset discards the writer's state and switches the Snappy writer to write to -// w. This permits reusing a Writer rather than allocating a new one. -func (w *Writer) Reset(writer io.Writer) { - w.w = writer - w.err = nil - if w.ibuf != nil { - w.ibuf = w.ibuf[:0] - } - w.wroteStreamHeader = false -} - -// Write satisfies the io.Writer interface. -func (w *Writer) Write(p []byte) (nRet int, errRet error) { - if w.ibuf == nil { - // Do not buffer incoming bytes. This does not perform or compress well - // if the caller of Writer.Write writes many small slices. This - // behavior is therefore deprecated, but still supported for backwards - // compatibility with code that doesn't explicitly Flush or Close. - return w.write(p) - } - - // The remainder of this method is based on bufio.Writer.Write from the - // standard library. - - for len(p) > (cap(w.ibuf)-len(w.ibuf)) && w.err == nil { - var n int - if len(w.ibuf) == 0 { - // Large write, empty buffer. - // Write directly from p to avoid copy. - n, _ = w.write(p) - } else { - n = copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p) - w.ibuf = w.ibuf[:len(w.ibuf)+n] - w.Flush() - } - nRet += n - p = p[n:] - } - if w.err != nil { - return nRet, w.err - } - n := copy(w.ibuf[len(w.ibuf):cap(w.ibuf)], p) - w.ibuf = w.ibuf[:len(w.ibuf)+n] - nRet += n - return nRet, nil -} - -func (w *Writer) write(p []byte) (nRet int, errRet error) { - if w.err != nil { - return 0, w.err - } - for len(p) > 0 { - obufStart := len(magicChunk) - if !w.wroteStreamHeader { - w.wroteStreamHeader = true - copy(w.obuf, magicChunk) - obufStart = 0 - } - - var uncompressed []byte - if len(p) > maxUncompressedChunkLen { - uncompressed, p = p[:maxUncompressedChunkLen], p[maxUncompressedChunkLen:] - } else { - uncompressed, p = p, nil - } - checksum := crc(uncompressed) - - // Compress the buffer, discarding the result if the improvement - // isn't at least 12.5%. - compressed := Encode(w.obuf[obufHeaderLen:], uncompressed) - chunkType := uint8(chunkTypeCompressedData) - chunkLen := 4 + len(compressed) - obufEnd := obufHeaderLen + len(compressed) - if len(compressed) >= len(uncompressed)-len(uncompressed)/8 { - chunkType = chunkTypeUncompressedData - chunkLen = 4 + len(uncompressed) - obufEnd = obufHeaderLen - } - - // Fill in the per-chunk header that comes before the body. - w.obuf[len(magicChunk)+0] = chunkType - w.obuf[len(magicChunk)+1] = uint8(chunkLen >> 0) - w.obuf[len(magicChunk)+2] = uint8(chunkLen >> 8) - w.obuf[len(magicChunk)+3] = uint8(chunkLen >> 16) - w.obuf[len(magicChunk)+4] = uint8(checksum >> 0) - w.obuf[len(magicChunk)+5] = uint8(checksum >> 8) - w.obuf[len(magicChunk)+6] = uint8(checksum >> 16) - w.obuf[len(magicChunk)+7] = uint8(checksum >> 24) - - if _, err := w.w.Write(w.obuf[obufStart:obufEnd]); err != nil { - w.err = err - return nRet, err - } - if chunkType == chunkTypeUncompressedData { - if _, err := w.w.Write(uncompressed); err != nil { - w.err = err - return nRet, err - } - } - nRet += len(uncompressed) - } - return nRet, nil -} - -// Flush flushes the Writer to its underlying io.Writer. -func (w *Writer) Flush() error { - if w.err != nil { - return w.err - } - if len(w.ibuf) == 0 { - return nil - } - w.write(w.ibuf) - w.ibuf = w.ibuf[:0] - return w.err -} - -// Close calls Flush and then closes the Writer. -func (w *Writer) Close() error { - w.Flush() - ret := w.err - if w.err == nil { - w.err = errClosed - } - return ret -} |