Scott Wood <[EMAIL PROTECTED]> wrote:
> int tmp;
>
> asm volatile("addi %1, %2, -1;"
> "andc %1, %2, %1;"
> "cntlzw %1, %1;"
> "subfic %0, %1, 31" : "=r" (j), "=&r" (tmp) : "r" (i));
Registers are usually assumed to be 'long' in size, so I'd recommend using
that rather than 'int' for tmp, though I suspect it'll make little difference
(except, perhaps on x86 where you can partially use registers).
> However, it'd be better to let the compiler do more, by just using the
> existing cntlzw() function.
Look in include/asm-powerpc/bitops.h. There are examples of the things you're
trying to do:
static __inline__ __attribute__((const))
int __ilog2(unsigned long x)
{
int lz;
asm (PPC_CNTLZL "%0,%1" : "=r" (lz) : "r" (x));
return BITS_PER_LONG - 1 - lz;
}
static __inline__ int __ffs(unsigned long x)
{
return __ilog2(x & -x);
}
Where:
asm-compat.h:79:#define PPC_CNTLZL stringify_in_c(cntlzd)
asm-compat.h:100:#define PPC_CNTLZL stringify_in_c(cntlzw)
Depending on whether you're in 32-bit mode or 64-bit mode.
David
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