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Date: Sat, 27 Oct 2007 15:27:01 +0200
From: "Christian \"Eddie\" Dost" <ecd@brainaid.de>
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Subject: Re: [Qemu-devel] Mips 64 emulation not compiling
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To: qemu-devel@nongnu.org

The sparc64 popc works in O(lg(n)), the "optimized" code below work in 
O(n). Could be better to generalize the sparc64 code, like this:

static always_inline int ctpop32 (uint32_t val)
{
	uint32_t i;

	i = (val & 0x55555555) + ((val >>  1) & 0x55555555);
	i = (i   & 0x33333333) + ((i   >>  2) & 0x33333333);
	i = (i   & 0x0f0f0f0f) + ((i   >>  4) & 0x0f0f0f0f);
	i = (i   & 0x00ff00ff) + ((i   >>  8) & 0x00ff00ff);
	i = (i   & 0x0000ffff) + ((i   >> 16) & 0x0000ffff);

	return i;
}

For the 64 bit version see target-sparc/op_helper.c

Best regards,
Eddie

Blue Swirl wrote:
> On 10/27/07, J. Mayer <l_indien@magic.fr> wrote:
>> I also got optimized versions of bit population count which could also
>> be shared:
>> static always_inline int ctpop32 (uint32_t val)
>> {
>>     int i;
>>
>>     for (i = 0; val != 0; i++)
>>         val = val ^ (val - 1);
>>
>>     return i;
>> }
>>
>> If you prefer, I can add those shared functions (ctz32, ctz64, cto32,
>> cto64, ctpop32, ctpop64) later, as they do not seem as widely used as
>> clxxx functions.
> 
> This would be interesting for Sparc64. Could you compare your version
> to do_popc() in target-sparc/op_helper.c?
> 
> 

-- 
___________________________________________________brainaid_____________
Eddie C. Dost           Rue de la Chapelle 51      phone +32 87 788817
                         B-4850 Moresnet            fax   +32 87 788818
ecd@brainaid.de         Belgium                    cell  +49 172 9312808