Use a bit for extra copy length in TagCopy4.

klauspost · Dec 11, 2023 · c928a8d · c928a8d
1 parent 617aeec
commit c928a8d
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Showing 2 changed files with 11 additions and 2 deletions.
diff --git a/s2/encode_best.go b/s2/encode_best.go
@@ -717,7 +717,11 @@ emitRemainder:
 func emitCopySize(offset, length int) int {
 	if offset >= 65536 {
 		// 3 Byte offset + Variable length (base length 4).
-		return 3 + emitRepeatSize(offset, length-3)
+		length -= 3
+		if length > 28 {
+			length -= 28
+		}
+		return 3 + emitRepeatSize(offset, length)
 	}
 
 	// Offset no more than 2 bytes.

diff --git a/s2/encode_go.go b/s2/encode_go.go
@@ -199,8 +199,13 @@ func encodeLength60(dst []byte, tag uint8, length int) int {
 func emitCopy(dst []byte, offset, length int) int {
 	offset--
 	if offset >= 65536 {
+		length = length - 3
 		// Encode tag+length as up to 4 bytes.
-		n := encodeLength(dst, tagCopy4, length-3)
+		if length > 28 {
+			offset |= 1 << 23
+			length -= 28
+		}
+		n := encodeLength(dst, tagCopy4, length)
 		// Encode offset as 3 bytes.
 		dst[n+2] = uint8(offset >> 16)
 		dst[n+1] = uint8(offset >> 8)