Catch overflow when incrementing src pointers.

decode.go

@@ -63,25 +63,25 @@ func Decode(dst, src []byte) ([]byte, error) {
 				s++
 			case x == 60:
 				s += 2
-				if s > len(src) {
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
 					return nil, ErrCorrupt
 				}
 				x = uint(src[s-1])
 			case x == 61:
 				s += 3
-				if s > len(src) {
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
 					return nil, ErrCorrupt
 				}
 				x = uint(src[s-2]) | uint(src[s-1])<<8
 			case x == 62:
 				s += 4
-				if s > len(src) {
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
 					return nil, ErrCorrupt
 				}
 				x = uint(src[s-3]) | uint(src[s-2])<<8 | uint(src[s-1])<<16
 			case x == 63:
 				s += 5
-				if s > len(src) {
+				if uint(s) > uint(len(src)) { // The uint conversions catch overflow from the previous line.
 					return nil, ErrCorrupt
 				}
 				x = uint(src[s-4]) | uint(src[s-3])<<8 | uint(src[s-2])<<16 | uint(src[s-1])<<24

encode.go

@@ -111,7 +111,7 @@ func Encode(dst, src []byte) []byte {
 		t   int // The last position with the same hash as s.
 		lit int // The start position of any pending literal bytes.
 	)
-	for s+3 < len(src) {
+	for uint(s+3) < uint(len(src)) { // The uint conversions catch overflow from the +3.
 		// Update the hash table.
 		b0, b1, b2, b3 := src[s], src[s+1], src[s+2], src[s+3]
 		h := uint32(b0) | uint32(b1)<<8 | uint32(b2)<<16 | uint32(b3)<<24