DragonTCP

go/internal/protocol/xor_fast32.go

@@ -0,0 +1,44 @@
+//go:build arm || 386
+
+package protocol
+
+import "unsafe"
+
+const xorWordMask32 uint32 = 0xADADADAD
+
+// XorInPlace is the 32-bit optimized path used by ARMv7/386 builds.
+// It aligns once, then processes 32 bytes per iteration with native uint32
+// operations instead of a byte-at-a-time loop.
+func XorInPlace(b []byte) {
+	n := len(b)
+	if n == 0 {
+		return
+	}
+
+	i := 0
+	for i < n && (uintptr(unsafe.Pointer(&b[i]))&3) != 0 {
+		b[i] ^= XORKey
+		i++
+	}
+
+	for ; i+32 <= n; i += 32 {
+		p := unsafe.Pointer(&b[i])
+		*(*uint32)(unsafe.Add(p, 0)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 4)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 8)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 12)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 16)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 20)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 24)) ^= xorWordMask32
+		*(*uint32)(unsafe.Add(p, 28)) ^= xorWordMask32
+	}
+
+	for ; i+4 <= n; i += 4 {
+		p := (*uint32)(unsafe.Pointer(&b[i]))
+		*p ^= xorWordMask32
+	}
+
+	for ; i < n; i++ {
+		b[i] ^= XORKey
+	}
+}