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// +build !amd64 appengine !gc noasm
package lz4
func decodeBlock(dst, src []byte) (ret int) {
const hasError = -2
defer func() {
if recover() != nil {
ret = hasError
}
}()
var si, di int
for {
// Literals and match lengths (token).
b := int(src[si])
si++
// Literals.
if lLen := b >> 4; lLen > 0 {
switch {
case lLen < 0xF && si+16 < len(src):
// Shortcut 1
// if we have enough room in src and dst, and the literals length
// is small enough (0..14) then copy all 16 bytes, even if not all
// are part of the literals.
copy(dst[di:], src[si:si+16])
si += lLen
di += lLen
if mLen := b & 0xF; mLen < 0xF {
// Shortcut 2
// if the match length (4..18) fits within the literals, then copy
// all 18 bytes, even if not all are part of the literals.
mLen += 4
if offset := int(src[si]) | int(src[si+1])<<8; mLen <= offset {
i := di - offset
end := i + 18
if end > len(dst) {
// The remaining buffer may not hold 18 bytes.
// See https://github.com/pierrec/lz4/issues/51.
end = len(dst)
}
copy(dst[di:], dst[i:end])
si += 2
di += mLen
continue
}
}
case lLen == 0xF:
for src[si] == 0xFF {
lLen += 0xFF
si++
}
lLen += int(src[si])
si++
fallthrough
default:
copy(dst[di:di+lLen], src[si:si+lLen])
si += lLen
di += lLen
}
}
if si >= len(src) {
return di
}
offset := int(src[si]) | int(src[si+1])<<8
if offset == 0 {
return hasError
}
si += 2
// Match.
mLen := b & 0xF
if mLen == 0xF {
for src[si] == 0xFF {
mLen += 0xFF
si++
}
mLen += int(src[si])
si++
}
mLen += minMatch
// Copy the match.
expanded := dst[di-offset:]
if mLen > offset {
// Efficiently copy the match dst[di-offset:di] into the dst slice.
bytesToCopy := offset * (mLen / offset)
for n := offset; n <= bytesToCopy+offset; n *= 2 {
copy(expanded[n:], expanded[:n])
}
di += bytesToCopy
mLen -= bytesToCopy
}
di += copy(dst[di:di+mLen], expanded[:mLen])
}
}
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