On Tue, Oct 17, 2006 at 11:12:56PM -0400, Adam Kropelin wrote:
...
> Write the code in userspace to prove it to yourself if you don't believe
> me. In fact, here. I did it for you. (x86 32 bit assumed; adjust to
> taste)
Thanks for the test code.
I'll resubmit with a patch that works for 32-bit extracts/implements
and integrate the more useful comments from this thread.
With just 1ULL and the original test, I get:
[EMAIL PROTECTED]:~$ ./test_extract
broken=0x61626364, working=0x00000000
The test code didn't attempt to correct for endianess...so the bytes
are backwards on gsyprf11. But 32-bit extract fails for offsets
1-7 like I expected.
I've rewritten the test to cover a few more cases.
And I've fixed the algorithm to handle 32-bit extracts in the test
below and will submit the same code in the next patch.
thanks,
grant
----------------------------------------------------------------------
/* test_extract.c */
#include <stdio.h>
typedef unsigned long u32;
typedef unsigned long long u64;
typedef unsigned char u8;
typedef unsigned long long __le64;
#define get_unaligned(x) (*(x)) /* kernel handles this though it might complain
*/
#ifdef __hppa__
/* copied from include/asm-parisc/byteorder.h */
#define __u32 u32
#define __u64 u64
static __u32 ___arch__swab32(__u32 x)
{
unsigned int temp;
__asm__("shd %0, %0, 16, %1\n\t" /* shift abcdabcd -> cdab */
"dep %1, 15, 8, %1\n\t" /* deposit cdab -> cbab */
"shd %0, %1, 8, %0" /* shift abcdcbab -> dcba */
: "=r" (x), "=&r" (temp)
: "0" (x));
return x;
}
static __inline__ __u64 le64_to_cpu(__u64 x)
{
__u32 t1 = ___arch__swab32((__u32) x);
__u32 t2 = ___arch__swab32((__u32) (x >> 32));
return (((__u64) t1 << 32) | t2);
}
#else
#define le64_to_cpu(x) (x)
#endif
static u32 working(u8 *report, unsigned offset, unsigned n)
{
report += (offset >> 5) << 2; offset &= 31;
return (le64_to_cpu(get_unaligned((__le64*)report)) >> offset) &
((1ULL << n) - 1);
}
static u32 broken(u8 *report, unsigned offset, unsigned n)
{
u64 x;
report += offset >> 3; /* adjust byte index */
offset &= 8 - 1;
x = get_unaligned((u64 *) report);
x = le64_to_cpu(x);
x = (x >> offset) & ((1ULL << n) - 1);
return x;
}
int main(int argc, char* argv)
{
unsigned int i;
u8 t[10] = { 0x10, 0x32, 0x54, 0x76, 0x98, 0xba, 0xdc, 0xfe, 0x10, 0x32
};
for (i = 0; i <= 40; i++)
printf("%2d : new 0x%08x orig 0x%08x\n", i,
broken(t, i, 32),
working(t, i, 32) );
return 0;
}
-------------------------------------------------------------------------
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