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Diffstat (limited to 'vendor/github.com/golang/snappy/encode_other.go')
| -rw-r--r-- | vendor/github.com/golang/snappy/encode_other.go | 238 |
1 files changed, 0 insertions, 238 deletions
diff --git a/vendor/github.com/golang/snappy/encode_other.go b/vendor/github.com/golang/snappy/encode_other.go deleted file mode 100644 index 296d7f0be..000000000 --- a/vendor/github.com/golang/snappy/encode_other.go +++ /dev/null @@ -1,238 +0,0 @@ -// Copyright 2016 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. - -// +build !amd64,!arm64 appengine !gc noasm - -package snappy - -func load32(b []byte, i int) uint32 { - b = b[i : i+4 : len(b)] // Help the compiler eliminate bounds checks on the next line. - return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24 -} - -func load64(b []byte, i int) uint64 { - b = b[i : i+8 : len(b)] // Help the compiler eliminate bounds checks on the next line. - return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 | - uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56 -} - -// emitLiteral writes a literal chunk and returns the number of bytes written. -// -// It assumes that: -// dst is long enough to hold the encoded bytes -// 1 <= len(lit) && len(lit) <= 65536 -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 - default: - dst[0] = 61<<2 | tagLiteral - dst[1] = uint8(n) - dst[2] = uint8(n >> 8) - i = 3 - } - return i + copy(dst[i:], lit) -} - -// emitCopy writes a copy chunk and returns the number of bytes written. -// -// It assumes that: -// dst is long enough to hold the encoded bytes -// 1 <= offset && offset <= 65535 -// 4 <= length && length <= 65535 -func emitCopy(dst []byte, offset, length int) int { - i := 0 - // The maximum length for a single tagCopy1 or tagCopy2 op is 64 bytes. The - // threshold for this loop is a little higher (at 68 = 64 + 4), and the - // length emitted down below is is a little lower (at 60 = 64 - 4), because - // it's shorter to encode a length 67 copy as a length 60 tagCopy2 followed - // by a length 7 tagCopy1 (which encodes as 3+2 bytes) than to encode it as - // a length 64 tagCopy2 followed by a length 3 tagCopy2 (which encodes as - // 3+3 bytes). The magic 4 in the 64±4 is because the minimum length for a - // tagCopy1 op is 4 bytes, which is why a length 3 copy has to be an - // encodes-as-3-bytes tagCopy2 instead of an encodes-as-2-bytes tagCopy1. - for length >= 68 { - // Emit a length 64 copy, encoded as 3 bytes. - dst[i+0] = 63<<2 | tagCopy2 - dst[i+1] = uint8(offset) - dst[i+2] = uint8(offset >> 8) - i += 3 - length -= 64 - } - if length > 64 { - // Emit a length 60 copy, encoded as 3 bytes. - dst[i+0] = 59<<2 | tagCopy2 - dst[i+1] = uint8(offset) - dst[i+2] = uint8(offset >> 8) - i += 3 - length -= 60 - } - if length >= 12 || offset >= 2048 { - // Emit the remaining copy, encoded as 3 bytes. - dst[i+0] = uint8(length-1)<<2 | tagCopy2 - dst[i+1] = uint8(offset) - dst[i+2] = uint8(offset >> 8) - return i + 3 - } - // Emit the remaining copy, encoded as 2 bytes. - dst[i+0] = uint8(offset>>8)<<5 | uint8(length-4)<<2 | tagCopy1 - dst[i+1] = uint8(offset) - return i + 2 -} - -// extendMatch returns the largest k such that k <= len(src) and that -// src[i:i+k-j] and src[j:k] have the same contents. -// -// It assumes that: -// 0 <= i && i < j && j <= len(src) -func extendMatch(src []byte, i, j int) int { - for ; j < len(src) && src[i] == src[j]; i, j = i+1, j+1 { - } - return j -} - -func hash(u, shift uint32) uint32 { - return (u * 0x1e35a7bd) >> shift -} - -// encodeBlock encodes a non-empty src to a guaranteed-large-enough dst. It -// assumes that the varint-encoded length of the decompressed bytes has already -// been written. -// -// It also assumes that: -// len(dst) >= MaxEncodedLen(len(src)) && -// minNonLiteralBlockSize <= len(src) && len(src) <= maxBlockSize -func encodeBlock(dst, src []byte) (d int) { - // Initialize the hash table. Its size ranges from 1<<8 to 1<<14 inclusive. - // The table element type is uint16, as s < sLimit and sLimit < len(src) - // and len(src) <= maxBlockSize and maxBlockSize == 65536. - const ( - maxTableSize = 1 << 14 - // tableMask is redundant, but helps the compiler eliminate bounds - // checks. - tableMask = maxTableSize - 1 - ) - shift := uint32(32 - 8) - for tableSize := 1 << 8; tableSize < maxTableSize && tableSize < len(src); tableSize *= 2 { - shift-- - } - // In Go, all array elements are zero-initialized, so there is no advantage - // to a smaller tableSize per se. However, it matches the C++ algorithm, - // and in the asm versions of this code, we can get away with zeroing only - // the first tableSize elements. - var table [maxTableSize]uint16 - - // sLimit is when to stop looking for offset/length copies. The inputMargin - // lets us use a fast path for emitLiteral in the main loop, while we are - // looking for copies. - sLimit := len(src) - inputMargin - - // nextEmit is where in src the next emitLiteral should start from. - nextEmit := 0 - - // The encoded form must start with a literal, as there are no previous - // bytes to copy, so we start looking for hash matches at s == 1. - s := 1 - nextHash := hash(load32(src, s), shift) - - for { - // Copied from the C++ snappy implementation: - // - // Heuristic match skipping: If 32 bytes are scanned with no matches - // found, start looking only at every other byte. If 32 more bytes are - // scanned (or skipped), look at every third byte, etc.. When a match - // is found, immediately go back to looking at every byte. This is a - // small loss (~5% performance, ~0.1% density) for compressible data - // due to more bookkeeping, but for non-compressible data (such as - // JPEG) it's a huge win since the compressor quickly "realizes" the - // data is incompressible and doesn't bother looking for matches - // everywhere. - // - // The "skip" variable keeps track of how many bytes there are since - // the last match; dividing it by 32 (ie. right-shifting by five) gives - // the number of bytes to move ahead for each iteration. - skip := 32 - - nextS := s - candidate := 0 - for { - s = nextS - bytesBetweenHashLookups := skip >> 5 - nextS = s + bytesBetweenHashLookups - skip += bytesBetweenHashLookups - if nextS > sLimit { - goto emitRemainder - } - candidate = int(table[nextHash&tableMask]) - table[nextHash&tableMask] = uint16(s) - nextHash = hash(load32(src, nextS), shift) - if load32(src, s) == load32(src, candidate) { - break - } - } - - // A 4-byte match has been found. We'll later see if more than 4 bytes - // match. But, prior to the match, src[nextEmit:s] are unmatched. Emit - // them as literal bytes. - d += emitLiteral(dst[d:], src[nextEmit:s]) - - // Call emitCopy, and then see if another emitCopy could be our next - // move. Repeat until we find no match for the input immediately after - // what was consumed by the last emitCopy call. - // - // If we exit this loop normally then we need to call emitLiteral next, - // though we don't yet know how big the literal will be. We handle that - // by proceeding to the next iteration of the main loop. We also can - // exit this loop via goto if we get close to exhausting the input. - for { - // Invariant: we have a 4-byte match at s, and no need to emit any - // literal bytes prior to s. - base := s - - // Extend the 4-byte match as long as possible. - // - // This is an inlined version of: - // s = extendMatch(src, candidate+4, s+4) - s += 4 - for i := candidate + 4; s < len(src) && src[i] == src[s]; i, s = i+1, s+1 { - } - - d += emitCopy(dst[d:], base-candidate, s-base) - nextEmit = s - if s >= sLimit { - goto emitRemainder - } - - // We could immediately start working at s now, but to improve - // compression we first update the hash table at s-1 and at s. If - // another emitCopy is not our next move, also calculate nextHash - // at s+1. At least on GOARCH=amd64, these three hash calculations - // are faster as one load64 call (with some shifts) instead of - // three load32 calls. - x := load64(src, s-1) - prevHash := hash(uint32(x>>0), shift) - table[prevHash&tableMask] = uint16(s - 1) - currHash := hash(uint32(x>>8), shift) - candidate = int(table[currHash&tableMask]) - table[currHash&tableMask] = uint16(s) - if uint32(x>>8) != load32(src, candidate) { - nextHash = hash(uint32(x>>16), shift) - s++ - break - } - } - } - -emitRemainder: - if nextEmit < len(src) { - d += emitLiteral(dst[d:], src[nextEmit:]) - } - return d -} |