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+---- Thread: small optimization idea (/Thread-small-optimization-idea)
small optimization idea - spacy51 - 08-18-2009 03:16 AM
gba-thumb.cpp @l1587:
Quote:// LDR Rd, [Rs, #Imm]Couldn't the highlighted block be optimized by replacing it with
static INSN_REGPARM void thumb68(u32 opcode)
{
if (busPrefetchCount == 0)
busPrefetch = busPrefetchEnable;
u32 address = reg[(opcode>>3)&7].I + (((opcode>>6)&31)<<2);
reg[opcode&7].I = CPUReadMemory(address);
clockTicks = 3 + dataTicksAccess32(address) + codeTicksAccess16(armNextPC);
}
Code:
((opcode>>4)&124)There are several cases like this around that area.
RE: small optimization idea - Zach Thibeau - 08-18-2009 05:46 AM
I'll give it a try and see what happens
RE: small optimization idea - Zach Thibeau - 08-18-2009 05:54 AM
ok tried
u32 address = reg[(opcode>>3)&7].I + (((opcode>>4)&124)<<2); and it didn't work (I know not what you said to try)
so then I tried
u32 address = reg[(opcode>>3)&7].I + (((opcode>>4)&124); compile didn't work since it was missing a bracket (that was kind of your fault for not giving the extra bracket
)once the extra bracket was added it worked again
u32 address = reg[(opcode>>3)&7].I + (((opcode>>4)&124));
and it was fairly optimized
RE: small optimization idea - spacy51 - 08-18-2009 06:08 AM
My replacement should be perfectly fine o.o
(08-18-2009 05:54 AM)Zach Thibeau Wrote: u32 address = reg[(opcode>>3)&7].I + (((opcode>>4)&124));
Do you seriously want to tell me there have to be two brackets???
It would be interesting to see the actual speed differences, if all of those similar code pieces were edited like that.
RE: small optimization idea - Zach Thibeau - 08-18-2009 06:09 AM
well I was tired and didn't notice >_< I didn't have my coffee at all but yeah I say let's do this as an experiment first before submitting it to svn and if the others like it then submit it
RE: small optimization idea - spacy51 - 08-18-2009 06:25 AM
It would be cool if some binary junky can tell me if the expression (((opcode>>6)&31)<<2) always gives the same results as ((opcode>>4)&124). I only had some basic binary term transformation in school ^^. I really don't want to introduce bugs like I did before I took a break xD
RE: small optimization idea - jbo_85 - 08-18-2009 06:28 AM
(08-18-2009 06:25 AM)spacy51 Wrote: It would be cool if some binary junky can tell me if the expression (((opcode>>6)&31)<<2) always gives the same results as ((opcode>>4)&124). I only had some basic binary term transformation in school ^^. I really don't want to introduce bugs like I did before I took a break xDThe two expressions are the same. But it doesn't make a difference for the release build because the compiler already optimizes it.
RE: small optimization idea - spacy51 - 08-18-2009 07:37 AM
Is there any proof that the compiler optimizes that? Hm, maybe it's possible to look at the assembler code the compiler produced.
RE: small optimization idea - jbo_85 - 08-18-2009 07:43 AM
I compared the executables.
RE: small optimization idea - spacy51 - 08-18-2009 08:04 AM
OK, good to know, thanks.