1 files changed, 188 insertions, 0 deletions
diff --git a/common/bitutil/bitutil.go b/common/bitutil/bitutil.go
new file mode 100644
index 000000000..117616543
--- /dev/null
+++ b/common/bitutil/bitutil.go
@@ -0,0 +1,188 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Adapted from: https://golang.org/src/crypto/cipher/xor.go
+
+// Package bitutil implements fast bitwise operations.
+package bitutil
+
+import (
+	"runtime"
+	"unsafe"
+)
+
+const wordSize = int(unsafe.Sizeof(uintptr(0)))
+const supportsUnaligned = runtime.GOARCH == "386" || runtime.GOARCH == "amd64" || runtime.GOARCH == "ppc64" || runtime.GOARCH == "ppc64le" || runtime.GOARCH == "s390x"
+
+// XORBytes xors the bytes in a and b. The destination is assumed to have enough
+// space. Returns the number of bytes xor'd.
+func XORBytes(dst, a, b []byte) int {
+	if supportsUnaligned {
+		return fastXORBytes(dst, a, b)
+	}
+	return safeXORBytes(dst, a, b)
+}
+
+// fastXORBytes xors in bulk. It only works on architectures that support
+// unaligned read/writes.
+func fastXORBytes(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	w := n / wordSize
+	if w > 0 {
+		dw := *(*[]uintptr)(unsafe.Pointer(&dst))
+		aw := *(*[]uintptr)(unsafe.Pointer(&a))
+		bw := *(*[]uintptr)(unsafe.Pointer(&b))
+		for i := 0; i < w; i++ {
+			dw[i] = aw[i] ^ bw[i]
+		}
+	}
+	for i := (n - n%wordSize); i < n; i++ {
+		dst[i] = a[i] ^ b[i]
+	}
+	return n
+}
+
+// safeXORBytes xors one by one. It works on all architectures, independent if
+// it supports unaligned read/writes or not.
+func safeXORBytes(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	for i := 0; i < n; i++ {
+		dst[i] = a[i] ^ b[i]
+	}
+	return n
+}
+
+// ANDBytes ands the bytes in a and b. The destination is assumed to have enough
+// space. Returns the number of bytes and'd.
+func ANDBytes(dst, a, b []byte) int {
+	if supportsUnaligned {
+		return fastANDBytes(dst, a, b)
+	}
+	return safeANDBytes(dst, a, b)
+}
+
+// fastANDBytes ands in bulk. It only works on architectures that support
+// unaligned read/writes.
+func fastANDBytes(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	w := n / wordSize
+	if w > 0 {
+		dw := *(*[]uintptr)(unsafe.Pointer(&dst))
+		aw := *(*[]uintptr)(unsafe.Pointer(&a))
+		bw := *(*[]uintptr)(unsafe.Pointer(&b))
+		for i := 0; i < w; i++ {
+			dw[i] = aw[i] & bw[i]
+		}
+	}
+	for i := (n - n%wordSize); i < n; i++ {
+		dst[i] = a[i] & b[i]
+	}
+	return n
+}
+
+// safeANDBytes ands one by one. It works on all architectures, independent if
+// it supports unaligned read/writes or not.
+func safeANDBytes(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	for i := 0; i < n; i++ {
+		dst[i] = a[i] & b[i]
+	}
+	return n
+}
+
+// ORBytes ors the bytes in a and b. The destination is assumed to have enough
+// space. Returns the number of bytes or'd.
+func ORBytes(dst, a, b []byte) int {
+	if supportsUnaligned {
+		return fastORBytes(dst, a, b)
+	}
+	return safeORBytes(dst, a, b)
+}
+
+// fastORBytes ors in bulk. It only works on architectures that support
+// unaligned read/writes.
+func fastORBytes(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	w := n / wordSize
+	if w > 0 {
+		dw := *(*[]uintptr)(unsafe.Pointer(&dst))
+		aw := *(*[]uintptr)(unsafe.Pointer(&a))
+		bw := *(*[]uintptr)(unsafe.Pointer(&b))
+		for i := 0; i < w; i++ {
+			dw[i] = aw[i] | bw[i]
+		}
+	}
+	for i := (n - n%wordSize); i < n; i++ {
+		dst[i] = a[i] | b[i]
+	}
+	return n
+}
+
+// safeORBytes ors one by one. It works on all architectures, independent if
+// it supports unaligned read/writes or not.
+func safeORBytes(dst, a, b []byte) int {
+	n := len(a)
+	if len(b) < n {
+		n = len(b)
+	}
+	for i := 0; i < n; i++ {
+		dst[i] = a[i] | b[i]
+	}
+	return n
+}
+
+// TestBytes tests whether any bit is set in the input byte slice.
+func TestBytes(p []byte) bool {
+	if supportsUnaligned {
+		return fastTestBytes(p)
+	}
+	return safeTestBytes(p)
+}
+
+// fastTestBytes tests for set bits in bulk. It only works on architectures that
+// support unaligned read/writes.
+func fastTestBytes(p []byte) bool {
+	n := len(p)
+	w := n / wordSize
+	if w > 0 {
+		pw := *(*[]uintptr)(unsafe.Pointer(&p))
+		for i := 0; i < w; i++ {
+			if pw[i] != 0 {
+				return true
+			}
+		}
+	}
+	for i := (n - n%wordSize); i < n; i++ {
+		if p[i] != 0 {
+			return true
+		}
+	}
+	return false
+}
+
+// safeTestBytes tests for set bits one byte at a time. It works on all
+// architectures, independent if it supports unaligned read/writes or not.
+func safeTestBytes(p []byte) bool {
+	for i := 0; i < len(p); i++ {
+		if p[i] != 0 {
+			return true
+		}
+	}
+	return false
+}