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Architectures and Processors forum How can i achieve a fixed timing using udiv?

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How can i achieve a fixed timing using udiv?

RBaeyens over 4 years ago

I am trying to generate a piece of code on an M4 with an exact known runtime, independent of the input.

Currently my bottleneck is that the duration of a division (udiv) is dependent on the input and therefore variable in execution time. Is there a way to ensure that my division lasts a same amount of instructions for each input?

Note: I am trying to write this with as minimal overhead as possible due to rather extreme execution time constraints.

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RBaeyens over 4 years ago in reply to 42Bastian Schick +2 verified

Hi Bastian, thanks a lot for your help. Currently I have used a cast to float such that it performs a float division which always lasts 14 cycles. Timingwise it's all stable now. Will try your proposition...
WestfW over 4 years ago +1

When does "early termination" happen? (how does up-to 63 leading zeros become 12 cycles or less?) With a 16bit numerator, presumably the range in number of cycles is smaller than if there were a full 32bit...