gallium/util: add helpers for bitfield manipulation

Add bitwise reversing and signed MSB helpers for software implementation
of the new TGSI opcodes.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>

src/gallium/auxiliary/util/u_math.h

@@ -567,6 +567,22 @@ static INLINE unsigned util_last_bit(unsigned u)
 #endif
 }
 
+/**
+ * Find last bit in a word that does not match the sign bit. The least
+ * significant bit is 1.
+ * Return 0 if no bits are set.
+ */
+static INLINE unsigned util_last_bit_signed(int i)
+{
+#if defined(__GNUC__) && ((__GNUC__ * 100 + __GNUC_MINOR__) >= 407)
+   return 31 - __builtin_clrsb(i);
+#else
+   if (i >= 0)
+      return util_last_bit(i);
+   else
+      return util_last_bit(~(unsigned)i);
+#endif
+}
 
 /* Destructively loop over all of the bits in a mask as in:
  *
@@ -715,6 +731,21 @@ util_bitcount(unsigned n)
 #endif
 }
 
+/**
+ * Reverse bits in n
+ * Algorithm taken from:
+ * http://stackoverflow.com/questions/9144800/c-reverse-bits-in-unsigned-integer
+ */
+static INLINE unsigned
+util_bitreverse(unsigned n)
+{
+    n = ((n >> 1) & 0x55555555u) | ((n & 0x55555555u) << 1);
+    n = ((n >> 2) & 0x33333333u) | ((n & 0x33333333u) << 2);
+    n = ((n >> 4) & 0x0f0f0f0fu) | ((n & 0x0f0f0f0fu) << 4);
+    n = ((n >> 8) & 0x00ff00ffu) | ((n & 0x00ff00ffu) << 8);
+    n = ((n >> 16) & 0xffffu) | ((n & 0xffffu) << 16);
+    return n;
+}
 
 /**
  * Convert from little endian to CPU byte order.