Difference between revisions of "Div and idiv (x86)"
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Latest revision as of 17:17, 7 January 2018
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Flesh out, include more than just caveats
Caveats
Both of these instructions are notoriously slow. If we do [ilmath]a%b[/ilmath] where [ilmath]0\le a<b[/ilmath] and [ilmath]b>0[/ilmath] then the result will be [ilmath]0[/ilmath] for the divisor and [ilmath]a[/ilmath] for the remainder. This is the trivial case, yet it's still really slow.
It is faster to do:
//for a,b unsigned integers if(a < b) { return a; } return a % b;
and similarly in the signed case, if the "return a" happens 80% of the time (this is from memory on Sandy Bridge arch, confirmed on Haswell.
