Somewhat faster xor_buf

Avoids the cast alignment problems of yesteryear

src/lib/utils/mem_ops.h

@@ -166,28 +166,25 @@ inline void xor_buf(uint8_t out[],
    {
    while(length >= 16)
       {
-      out[0] ^= in[0];
-      out[1] ^= in[1];
-      out[2] ^= in[2];
-      out[3] ^= in[3];
-      out[4] ^= in[4];
-      out[5] ^= in[5];
-      out[6] ^= in[6];
-      out[7] ^= in[7];
-      out[8] ^= in[8];
-      out[9] ^= in[9];
-      out[10] ^= in[10];
-      out[11] ^= in[11];
-      out[12] ^= in[12];
-      out[13] ^= in[13];
-      out[14] ^= in[14];
-      out[15] ^= in[15];
+      uint64_t x0, x1, y0, y1;
+      memcpy(&x0, in, 8);
+      memcpy(&x1, in + 8, 8);
+      memcpy(&y0, out, 8);
+      memcpy(&y1, out + 8, 8);
+
+      y0 ^= x0;
+      y1 ^= x1;
+      memcpy(out, &y0, 8);
+      memcpy(out + 8, &y1, 8);
       out += 16; in += 16; length -= 16;
       }
 
-   for(size_t i = 0; i != length; ++i)
+   while(length > 0)
       {
-      out[i] ^= in[i];
+      out[0] ^= in[0];
+      out += 1;
+      in += 1;
+      length -= 1;
       }
    }