+2005-05-09 Richard Earnshaw <richard.earnshaw@arm.com>
+
+ * arm.c (arm_gen_constant): Add new heuristic for generating
+ constant integers that can be expressed as the difference of two
+ valid immediates.
+
2005-05-09 Roger Sayle <roger@eyesopen.com>
* c-tree.h (parser_build_unary_op): New prototype.
int
const_ok_for_arm (HOST_WIDE_INT i)
{
- unsigned HOST_WIDE_INT mask = ~(unsigned HOST_WIDE_INT)0xFF;
-
+ int lowbit;
+
/* For machines with >32 bit HOST_WIDE_INT, the bits above bit 31 must
be all zero, or all one. */
if ((i & ~(unsigned HOST_WIDE_INT) 0xffffffff) != 0
& ~(unsigned HOST_WIDE_INT) 0xffffffff)))
return FALSE;
- /* Fast return for 0 and powers of 2 */
- if ((i & (i - 1)) == 0)
+ i &= (unsigned HOST_WIDE_INT) 0xffffffff;
+
+ /* Fast return for 0 and small values. We must do this for zero, since
+ the code below can't handle that one case. */
+ if ((i & ~(unsigned HOST_WIDE_INT) 0xff) == 0)
return TRUE;
- do
- {
- if ((i & mask & (unsigned HOST_WIDE_INT) 0xffffffff) == 0)
- return TRUE;
- mask =
- (mask << 2) | ((mask & (unsigned HOST_WIDE_INT) 0xffffffff)
- >> (32 - 2)) | ~(unsigned HOST_WIDE_INT) 0xffffffff;
- }
- while (mask != ~(unsigned HOST_WIDE_INT) 0xFF);
+ /* Get the number of trailing zeros, rounded down to the nearest even
+ number. */
+ lowbit = (ffs ((int) i) - 1) & ~1;
+
+ if ((i & ~(((unsigned HOST_WIDE_INT) 0xff) << lowbit)) == 0)
+ return TRUE;
+ else if (lowbit <= 4
+ && ((i & ~0xc000003f) == 0
+ || (i & ~0xf000000f) == 0
+ || (i & ~0xfc000003) == 0))
+ return TRUE;
return FALSE;
}