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authorNicolas Pitre <nico@cam.org>2006-01-10 19:48:02 +0000
committerRussell King <rmk+kernel@arm.linux.org.uk>2006-01-10 19:48:02 +0000
commita3e49436867e6c7acc1b5eed21d30c88d156825b (patch)
tree1460c6474c721eaabf3f84f5df4a6a72b90f9621 /include/asm-arm/byteorder.h
parentb016450f9f603210239e1a91e3c28f17c310dcc7 (diff)
[ARM] 3252/1: help gcc do the best with ___arch__swab32
Patch from Nicolas Pitre Depending on your gcc version, the current C-only implementation would produce suboptimal code, ranging from a bad register selection forcing an additional mov instruction to a failure to merge the eor and the ror in a single instruction. With a little help gcc always produces the best code. Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
Diffstat (limited to 'include/asm-arm/byteorder.h')
-rw-r--r--include/asm-arm/byteorder.h11
1 files changed, 10 insertions, 1 deletions
diff --git a/include/asm-arm/byteorder.h b/include/asm-arm/byteorder.h
index 741f5bc5d01..17eaf8bdf09 100644
--- a/include/asm-arm/byteorder.h
+++ b/include/asm-arm/byteorder.h
@@ -22,7 +22,16 @@ static inline __attribute_const__ __u32 ___arch__swab32(__u32 x)
{
__u32 t;
- t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
+ if (__builtin_constant_p(x)) {
+ t = x ^ ((x << 16) | (x >> 16)); /* eor r1,r0,r0,ror #16 */
+ } else {
+ /*
+ * The compiler needs a bit of a hint here to always do the
+ * right thing and not screw it up to different degrees
+ * depending on the gcc version.
+ */
+ asm ("eor\t%0, %1, %1, ror #16" : "=r" (t) : "r" (x));
+ }
x = (x << 24) | (x >> 8); /* mov r0,r0,ror #8 */
t &= ~0x00FF0000; /* bic r1,r1,#0x00FF0000 */
x ^= (t >> 8); /* eor r0,r0,r1,lsr #8 */