internal/compress: Import flate and such from klauspost/compress

1 files changed, 34 insertions, 0 deletions

diff --git a/internal/compress/flate/matchlen_generic.go b/internal/compress/flate/matchlen_generic.go
new file mode 100644
index 00000000..63c0637d
--- /dev/null
+++ b/internal/compress/flate/matchlen_generic.go
@@ -0,0 +1,34 @@
+// Copyright 2019+ Klaus Post. All rights reserved.
+// License information can be found in the LICENSE file.
+
+package flate
+
+import (
+	"math/bits"
+
+	"codeberg.org/lindenii/furgit/internal/compress/internal/le"
+)
+
+// matchLen returns the maximum common prefix length of a and b.
+// a must be the shortest of the two.
+func matchLen(a, b []byte) (n int) {
+	left := len(a)
+	for left >= 8 {
+		diff := le.Load64(a, n) ^ le.Load64(b, n)
+		if diff != 0 {
+			return n + bits.TrailingZeros64(diff)>>3
+		}
+		n += 8
+		left -= 8
+	}
+
+	a = a[n:]
+	b = b[n:]
+	for i := range a {
+		if a[i] != b[i] {
+			break
+		}
+		n++
+	}
+	return n
+}