optimization - C/Arm4 Mult and Division performance -


i trying optimize code going used on arm architecture.

the target architecture arm9 architecture doesn't support fpcalculations, , testing configuration arm4 emulation in vs2008. have tried run comparisons see if it's worth attempting change divisions multiplications , i've ran interesting results don't understand.

here code ran:

for(int = 0; < testrate; i++){     num = 356.0f * 0.06666666666666666666666666666667f; } queryperformancecounter( &end ); double result1 = end.quadpart - start.quadpart;  queryperformancecounter( &start ); for(int = 0; < testrate; i++)     num2 = 356.0f / 15.0f ; queryperformancecounter( &end ); double result2 = end.quadpart - start.quadpart;

and result:

calculation time 1: 1485016.000000, result : 23.733335  calculation time 2: 1068092.000000, result : 23.733334

calculation 1 when done multiplications , calculation 2 divisions. result shows divisions faster , on better cases difference between 2 calculations become negligible. here testrate = 1000000.

i know multiplications have fixed cycle divisions can take 24 cycles @ worst case, same arm architecture? in code trying port have various divisions have dynamic denominators considering using fast reciprocal function reciprocal , multiply instead of dividing it, , based on result test above i'm thinking might not render result expecting. can clarify me?


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