Use arrays for constant size copies (klauspost#659)

* Use arrays for constant size copies Requires Go 1.17
burmilla · Sep 9, 2022 · 5d754d7 · 5d754d7
1 parent 49d8cf2
commit 5d754d7
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Showing 7 changed files with 51 additions and 30 deletions.
diff --git a/flate/deflate.go b/flate/deflate.go
@@ -131,7 +131,8 @@ func (d *compressor) fillDeflate(b []byte) int {
 	s := d.state
 	if s.index >= 2*windowSize-(minMatchLength+maxMatchLength) {
 		// shift the window by windowSize
-		copy(d.window[:], d.window[windowSize:2*windowSize])
+		//copy(d.window[:], d.window[windowSize:2*windowSize])
+		*(*[windowSize]byte)(d.window) = *(*[windowSize]byte)(d.window[windowSize:])
 		s.index -= windowSize
 		d.windowEnd -= windowSize
 		if d.blockStart >= windowSize {

diff --git a/flate/fast_encoder.go b/flate/fast_encoder.go
@@ -104,7 +104,8 @@ func (e *fastGen) addBlock(src []byte) int32 {
 			}
 			// Move down
 			offset := int32(len(e.hist)) - maxMatchOffset
-			copy(e.hist[0:maxMatchOffset], e.hist[offset:])
+			// copy(e.hist[0:maxMatchOffset], e.hist[offset:])
+			*(*[maxMatchOffset]byte)(e.hist) = *(*[maxMatchOffset]byte)(e.hist[offset:])
 			e.cur += offset
 			e.hist = e.hist[:maxMatchOffset]
 		}

diff --git a/flate/huffman_bit_writer.go b/flate/huffman_bit_writer.go
@@ -790,9 +790,11 @@ func (w *huffmanBitWriter) fillTokens() {
 // and offsetEncoding.
 // The number of literal and offset tokens is returned.
 func (w *huffmanBitWriter) indexTokens(t *tokens, filled bool) (numLiterals, numOffsets int) {
-	copy(w.literalFreq[:], t.litHist[:])
-	copy(w.literalFreq[256:], t.extraHist[:])
-	copy(w.offsetFreq[:], t.offHist[:offsetCodeCount])
+	//copy(w.literalFreq[:], t.litHist[:])
+	*(*[256]uint16)(w.literalFreq[:]) = t.litHist
+	//copy(w.literalFreq[256:], t.extraHist[:])
+	*(*[32]uint16)(w.literalFreq[256:]) = t.extraHist
+	w.offsetFreq = t.offHist
 
 	if t.n == 0 {
 		return

diff --git a/huff0/decompress.go b/huff0/decompress.go
@@ -763,17 +763,20 @@ func (d *Decoder) decompress4X8bit(dst, src []byte) ([]byte, error) {
 				d.bufs.Put(buf)
 				return nil, errors.New("corruption detected: stream overrun 1")
 			}
-			copy(out, buf[0][:])
-			copy(out[dstEvery:], buf[1][:])
-			copy(out[dstEvery*2:], buf[2][:])
-			copy(out[dstEvery*3:], buf[3][:])
-			out = out[bufoff:]
-			decoded += bufoff * 4
 			// There must at least be 3 buffers left.
-			if len(out) < dstEvery*3 {
+			if len(out)-bufoff < dstEvery*3 {
 				d.bufs.Put(buf)
 				return nil, errors.New("corruption detected: stream overrun 2")
 			}
+			//copy(out, buf[0][:])
+			//copy(out[dstEvery:], buf[1][:])
+			//copy(out[dstEvery*2:], buf[2][:])
+			*(*[bufoff]byte)(out) = buf[0]
+			*(*[bufoff]byte)(out[dstEvery:]) = buf[1]
+			*(*[bufoff]byte)(out[dstEvery*2:]) = buf[2]
+			*(*[bufoff]byte)(out[dstEvery*3:]) = buf[3]
+			out = out[bufoff:]
+			decoded += bufoff * 4
 		}
 	}
 	if off > 0 {
@@ -997,17 +1000,22 @@ func (d *Decoder) decompress4X8bitExactly(dst, src []byte) ([]byte, error) {
 				d.bufs.Put(buf)
 				return nil, errors.New("corruption detected: stream overrun 1")
 			}
-			copy(out, buf[0][:])
-			copy(out[dstEvery:], buf[1][:])
-			copy(out[dstEvery*2:], buf[2][:])
-			copy(out[dstEvery*3:], buf[3][:])
-			out = out[bufoff:]
-			decoded += bufoff * 4
 			// There must at least be 3 buffers left.
-			if len(out) < dstEvery*3 {
+			if len(out)-bufoff < dstEvery*3 {
 				d.bufs.Put(buf)
 				return nil, errors.New("corruption detected: stream overrun 2")
 			}
+
+			//copy(out, buf[0][:])
+			//copy(out[dstEvery:], buf[1][:])
+			//copy(out[dstEvery*2:], buf[2][:])
+			// copy(out[dstEvery*3:], buf[3][:])
+			*(*[bufoff]byte)(out) = buf[0]
+			*(*[bufoff]byte)(out[dstEvery:]) = buf[1]
+			*(*[bufoff]byte)(out[dstEvery*2:]) = buf[2]
+			*(*[bufoff]byte)(out[dstEvery*3:]) = buf[3]
+			out = out[bufoff:]
+			decoded += bufoff * 4
 		}
 	}
 	if off > 0 {

diff --git a/huff0/decompress_generic.go b/huff0/decompress_generic.go
@@ -122,17 +122,21 @@ func (d *Decoder) Decompress4X(dst, src []byte) ([]byte, error) {
 				d.bufs.Put(buf)
 				return nil, errors.New("corruption detected: stream overrun 1")
 			}
-			copy(out, buf[0][:])
-			copy(out[dstEvery:], buf[1][:])
-			copy(out[dstEvery*2:], buf[2][:])
-			copy(out[dstEvery*3:], buf[3][:])
-			out = out[bufoff:]
-			decoded += bufoff * 4
 			// There must at least be 3 buffers left.
-			if len(out) < dstEvery*3 {
+			if len(out)-bufoff < dstEvery*3 {
 				d.bufs.Put(buf)
 				return nil, errors.New("corruption detected: stream overrun 2")
 			}
+			//copy(out, buf[0][:])
+			//copy(out[dstEvery:], buf[1][:])
+			//copy(out[dstEvery*2:], buf[2][:])
+			//copy(out[dstEvery*3:], buf[3][:])
+			*(*[bufoff]byte)(out) = buf[0]
+			*(*[bufoff]byte)(out[dstEvery:]) = buf[1]
+			*(*[bufoff]byte)(out[dstEvery*2:]) = buf[2]
+			*(*[bufoff]byte)(out[dstEvery*3:]) = buf[3]
+			out = out[bufoff:]
+			decoded += bufoff * 4
 		}
 	}
 	if off > 0 {

diff --git a/zstd/enc_dfast.go b/zstd/enc_dfast.go
@@ -1103,7 +1103,8 @@ func (e *doubleFastEncoderDict) Reset(d *dict, singleBlock bool) {
 	}
 
 	if allDirty || dirtyShardCnt > dLongTableShardCnt/2 {
-		copy(e.longTable[:], e.dictLongTable)
+		//copy(e.longTable[:], e.dictLongTable)
+		e.longTable = *(*[dFastLongTableSize]tableEntry)(e.dictLongTable)
 		for i := range e.longTableShardDirty {
 			e.longTableShardDirty[i] = false
 		}
@@ -1114,7 +1115,9 @@ func (e *doubleFastEncoderDict) Reset(d *dict, singleBlock bool) {
 			continue
 		}
 
-		copy(e.longTable[i*dLongTableShardSize:(i+1)*dLongTableShardSize], e.dictLongTable[i*dLongTableShardSize:(i+1)*dLongTableShardSize])
+		// copy(e.longTable[i*dLongTableShardSize:(i+1)*dLongTableShardSize], e.dictLongTable[i*dLongTableShardSize:(i+1)*dLongTableShardSize])
+		*(*[dLongTableShardSize]tableEntry)(e.longTable[i*dLongTableShardSize:]) = *(*[dLongTableShardSize]tableEntry)(e.dictLongTable[i*dLongTableShardSize:])
+
 		e.longTableShardDirty[i] = false
 	}
 }

diff --git a/zstd/enc_fast.go b/zstd/enc_fast.go
@@ -871,7 +871,8 @@ func (e *fastEncoderDict) Reset(d *dict, singleBlock bool) {
 	const shardCnt = tableShardCnt
 	const shardSize = tableShardSize
 	if e.allDirty || dirtyShardCnt > shardCnt*4/6 {
-		copy(e.table[:], e.dictTable)
+		//copy(e.table[:], e.dictTable)
+		e.table = *(*[tableSize]tableEntry)(e.dictTable)
 		for i := range e.tableShardDirty {
 			e.tableShardDirty[i] = false
 		}
@@ -883,7 +884,8 @@ func (e *fastEncoderDict) Reset(d *dict, singleBlock bool) {
 			continue
 		}
 
-		copy(e.table[i*shardSize:(i+1)*shardSize], e.dictTable[i*shardSize:(i+1)*shardSize])
+		//copy(e.table[i*shardSize:(i+1)*shardSize], e.dictTable[i*shardSize:(i+1)*shardSize])
+		*(*[shardSize]tableEntry)(e.table[i*shardSize:]) = *(*[shardSize]tableEntry)(e.dictTable[i*shardSize:])
 		e.tableShardDirty[i] = false
 	}
 	e.allDirty = false