diff options
| author | Nicolas Pitre <nico@cam.org> | 2006-01-10 19:48:02 +0000 |
|---|---|---|
| committer | Russell King <rmk+kernel@arm.linux.org.uk> | 2006-01-10 19:48:02 +0000 |
| commit | a3e49436867e6c7acc1b5eed21d30c88d156825b (patch) | |
| tree | 1460c6474c721eaabf3f84f5df4a6a72b90f9621 /include/asm-arm/byteorder.h | |
| parent | b016450f9f603210239e1a91e3c28f17c310dcc7 (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.h | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/include/asm-arm/byteorder.h b/include/asm-arm/byteorder.h index 741f5bc5d016..17eaf8bdf092 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 */ |