Use "table look-up" method for reversing byte

This method takes constant time and is less prone to (CPU) pipeline stalling due to less
computation. Also it is slightly faster than the previous method.

src/base/bittorrent/ltqbitarray.cpp

@@ -37,8 +37,18 @@ namespace
 {
     unsigned char reverseByte(const unsigned char byte)
     {
-        // https://graphics.stanford.edu/~seander/bithacks.html#ReverseByteWith64Bits
-        return (((byte * 0x80200802ULL) & 0x0884422110ULL) * 0x0101010101ULL) >> 32;
+        // https://graphics.stanford.edu/~seander/bithacks.html#BitReverseTable
+        static const unsigned char table[] =
+        {
+#define R2(n) n, (n + (2 * 64)), (n + 64), (n + (3 * 64))
+#define R4(n) R2(n), R2(n + (2 * 16)), R2(n + 16), R2(n + (3 * 16))
+#define R6(n) R4(n), R4(n + (2 * 4)), R4(n + 4), R4(n + (3 * 4))
+            R6(0), R6(2), R6(1), R6(3)
+#undef R6
+#undef R4
+#undef R2
+        };
+        return table[byte];
     }
 }