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|
//go:build !amd64 || appengine || !gc || noasm
// +build !amd64 appengine !gc noasm
package s2
import (
"math/bits"
)
// 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))
func encodeBlock(dst, src []byte) (d int) {
if len(src) < minNonLiteralBlockSize {
return 0
}
return encodeBlockGo(dst, src)
}
// encodeBlockBetter 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))
func encodeBlockBetter(dst, src []byte) (d int) {
return encodeBlockBetterGo(dst, src)
}
// encodeBlockBetter 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))
func encodeBlockBetterSnappy(dst, src []byte) (d int) {
return encodeBlockBetterSnappyGo(dst, src)
}
// 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))
func encodeBlockSnappy(dst, src []byte) (d int) {
if len(src) < minNonLiteralBlockSize {
return 0
}
return encodeBlockSnappyGo(dst, src)
}
// emitLiteral writes a literal chunk and returns the number of bytes written.
//
// It assumes that:
// dst is long enough to hold the encoded bytes
// 0 <= len(lit) && len(lit) <= math.MaxUint32
func emitLiteral(dst, lit []byte) int {
if len(lit) == 0 {
return 0
}
const num = 63<<2 | tagLiteral
i, n := 0, uint(len(lit)-1)
switch {
case n < 60:
dst[0] = uint8(n)<<2 | tagLiteral
i = 1
case n < 1<<8:
dst[1] = uint8(n)
dst[0] = 60<<2 | tagLiteral
i = 2
case n < 1<<16:
dst[2] = uint8(n >> 8)
dst[1] = uint8(n)
dst[0] = 61<<2 | tagLiteral
i = 3
case n < 1<<24:
dst[3] = uint8(n >> 16)
dst[2] = uint8(n >> 8)
dst[1] = uint8(n)
dst[0] = 62<<2 | tagLiteral
i = 4
default:
dst[4] = uint8(n >> 24)
dst[3] = uint8(n >> 16)
dst[2] = uint8(n >> 8)
dst[1] = uint8(n)
dst[0] = 63<<2 | tagLiteral
i = 5
}
return i + copy(dst[i:], lit)
}
// emitRepeat writes a repeat chunk and returns the number of bytes written.
// Length must be at least 4 and < 1<<24
func emitRepeat(dst []byte, offset, length int) int {
// Repeat offset, make length cheaper
length -= 4
if length <= 4 {
dst[0] = uint8(length)<<2 | tagCopy1
dst[1] = 0
return 2
}
if length < 8 && offset < 2048 {
// Encode WITH offset
dst[1] = uint8(offset)
dst[0] = uint8(offset>>8)<<5 | uint8(length)<<2 | tagCopy1
return 2
}
if length < (1<<8)+4 {
length -= 4
dst[2] = uint8(length)
dst[1] = 0
dst[0] = 5<<2 | tagCopy1
return 3
}
if length < (1<<16)+(1<<8) {
length -= 1 << 8
dst[3] = uint8(length >> 8)
dst[2] = uint8(length >> 0)
dst[1] = 0
dst[0] = 6<<2 | tagCopy1
return 4
}
const maxRepeat = (1 << 24) - 1
length -= 1 << 16
left := 0
if length > maxRepeat {
left = length - maxRepeat + 4
length = maxRepeat - 4
}
dst[4] = uint8(length >> 16)
dst[3] = uint8(length >> 8)
dst[2] = uint8(length >> 0)
dst[1] = 0
dst[0] = 7<<2 | tagCopy1
if left > 0 {
return 5 + emitRepeat(dst[5:], offset, left)
}
return 5
}
// 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 <= math.MaxUint32
// 4 <= length && length <= 1 << 24
func emitCopy(dst []byte, offset, length int) int {
if offset >= 65536 {
i := 0
if length > 64 {
// Emit a length 64 copy, encoded as 5 bytes.
dst[4] = uint8(offset >> 24)
dst[3] = uint8(offset >> 16)
dst[2] = uint8(offset >> 8)
dst[1] = uint8(offset)
dst[0] = 63<<2 | tagCopy4
length -= 64
if length >= 4 {
// Emit remaining as repeats
return 5 + emitRepeat(dst[5:], offset, length)
}
i = 5
}
if length == 0 {
return i
}
// Emit a copy, offset encoded as 4 bytes.
dst[i+0] = uint8(length-1)<<2 | tagCopy4
dst[i+1] = uint8(offset)
dst[i+2] = uint8(offset >> 8)
dst[i+3] = uint8(offset >> 16)
dst[i+4] = uint8(offset >> 24)
return i + 5
}
// Offset no more than 2 bytes.
if length > 64 {
// Emit a length 60 copy, encoded as 3 bytes.
// Emit remaining as repeat value (minimum 4 bytes).
dst[2] = uint8(offset >> 8)
dst[1] = uint8(offset)
dst[0] = 59<<2 | tagCopy2
length -= 60
// Emit remaining as repeats, at least 4 bytes remain.
return 3 + emitRepeat(dst[3:], offset, length)
}
if length >= 12 || offset >= 2048 {
// Emit the remaining copy, encoded as 3 bytes.
dst[2] = uint8(offset >> 8)
dst[1] = uint8(offset)
dst[0] = uint8(length-1)<<2 | tagCopy2
return 3
}
// Emit the remaining copy, encoded as 2 bytes.
dst[1] = uint8(offset)
dst[0] = uint8(offset>>8)<<5 | uint8(length-4)<<2 | tagCopy1
return 2
}
// emitCopyNoRepeat 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 <= math.MaxUint32
// 4 <= length && length <= 1 << 24
func emitCopyNoRepeat(dst []byte, offset, length int) int {
if offset >= 65536 {
i := 0
if length > 64 {
// Emit a length 64 copy, encoded as 5 bytes.
dst[4] = uint8(offset >> 24)
dst[3] = uint8(offset >> 16)
dst[2] = uint8(offset >> 8)
dst[1] = uint8(offset)
dst[0] = 63<<2 | tagCopy4
length -= 64
if length >= 4 {
// Emit remaining as repeats
return 5 + emitCopyNoRepeat(dst[5:], offset, length)
}
i = 5
}
if length == 0 {
return i
}
// Emit a copy, offset encoded as 4 bytes.
dst[i+0] = uint8(length-1)<<2 | tagCopy4
dst[i+1] = uint8(offset)
dst[i+2] = uint8(offset >> 8)
dst[i+3] = uint8(offset >> 16)
dst[i+4] = uint8(offset >> 24)
return i + 5
}
// Offset no more than 2 bytes.
if length > 64 {
// Emit a length 60 copy, encoded as 3 bytes.
// Emit remaining as repeat value (minimum 4 bytes).
dst[2] = uint8(offset >> 8)
dst[1] = uint8(offset)
dst[0] = 59<<2 | tagCopy2
length -= 60
// Emit remaining as repeats, at least 4 bytes remain.
return 3 + emitCopyNoRepeat(dst[3:], offset, length)
}
if length >= 12 || offset >= 2048 {
// Emit the remaining copy, encoded as 3 bytes.
dst[2] = uint8(offset >> 8)
dst[1] = uint8(offset)
dst[0] = uint8(length-1)<<2 | tagCopy2
return 3
}
// Emit the remaining copy, encoded as 2 bytes.
dst[1] = uint8(offset)
dst[0] = uint8(offset>>8)<<5 | uint8(length-4)<<2 | tagCopy1
return 2
}
// matchLen returns how many bytes match in a and b
//
// It assumes that:
// len(a) <= len(b)
//
func matchLen(a []byte, b []byte) int {
b = b[:len(a)]
var checked int
if len(a) > 4 {
// Try 4 bytes first
if diff := load32(a, 0) ^ load32(b, 0); diff != 0 {
return bits.TrailingZeros32(diff) >> 3
}
// Switch to 8 byte matching.
checked = 4
a = a[4:]
b = b[4:]
for len(a) >= 8 {
b = b[:len(a)]
if diff := load64(a, 0) ^ load64(b, 0); diff != 0 {
return checked + (bits.TrailingZeros64(diff) >> 3)
}
checked += 8
a = a[8:]
b = b[8:]
}
}
b = b[:len(a)]
for i := range a {
if a[i] != b[i] {
return int(i) + checked
}
}
return len(a) + checked
}
|
