[parisc-linux] byte swapping redux

Grant Grundler grundler@parisc-linux.org
Tue, 1 Jul 2003 12:13:27 -0600

On Tue, Jul 01, 2003 at 06:33:07PM +0200, Joel Soete wrote:
> I hope I am not going to anoying you.


> I just found related interesting stuff: <http://lwn.net/Articles/38384/>
> And may be also the source of pb.

Maybe our userspace will encounter this problem as well since I've
ripped out the __STRICT_ANSI__ test...can you work this out?

> I also write this small testcase to try to point out the pb in 32bits mode:
> And here is the results:
> Val of TU64: fedcba9876543210
> Val of ___arch__swab64(TU64): 76543210fedcba98
> Val of __fswab64(TU64): 1032547698badcfe
> What is right (I could not rebuild with hppa64-linux-gcc :( )?

__fswab64() is correct.
___arch__swab64() didn't actually swap within the  32-bit words.

asm-parisc/byteorder.h has:
static __inline__ __const__ __u64 ___arch__swab64(__u64 x)
	__u32 t1 = (__u32) x;
	__u32 t2 = (__u32) ((x) >> 32);
	return (((__u64) t2 << 32) + ((__u64) t1));

DOH! *smack*
Probably my bad.
That should read:

static __inline__ __const__ __u64 ___arch__swab64(__u64 x)
	__u32 t1 = (__u32) x;
	__u32 t2 = (__u32) ((x) >> 32);
	return ((__u64) ___arch__swab32(t1) << 32) + ((__u64) ___arch__swab32(t2));     

Could you please test this?