Kevin Diggs <[EMAIL PROTECTED]> writes:
> Jeremy Kerr wrote:
>> Hi Kevin,
>>
>>
>>> /*
>>> * Turn r3 (range) into a rotate count for the selected
>>>range. * 0 -> 23, 1 -> 31
>>> */
>>> __asm__ __volatile__ ( "slwi %0,%0,3\n"
>>> "addi %0,%0,23\n"
>>> "rlwnm %0,%1,%0,30,31\n":
>>> "=r"(ret):
>>> "r"(config),"0"(range)
>>> );
>>
>>
>> Wouldn't this be much simpler in plain C?
>>
> I just knew someone was gonna try to rain on my rlwnm'in fun parade!
> Wonder if the C code can be made to compile down to 3 instructions?
This will do:
unsigned int get_PLL_range(unsigned int range, unsigned int config)
{
range = range * 8 + 23;
return ((config << range) | (config >> (32 - range))) & 3;
}
The special pattern ((a << n) | (a >> (32 - n))) is recognized by gcc as
a rotate operation.
Andreas.
--
Andreas Schwab, SuSE Labs, [EMAIL PROTECTED]
SuSE Linux Products GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
PGP key fingerprint = 58CA 54C7 6D53 942B 1756 01D3 44D5 214B 8276 4ED5
"And now for something completely different."
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