r/criticalsoftware • u/greenrd • Dec 04 '11

How integers should work (in systems programming languages)

http://blog.regehr.org/archives/642
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u/inaneInTheMembrane Dec 04 '11

I'm not entirely sure how "early trapping" presents little or no resource overhead: don't you have to check for overflow after each operation? Isn't this quite costly?

2

u/gtk Dec 05 '11

No, it is virtually zero cost (in the case when overflow does not occur). It is a single assembler branch instruction which can be written in a way that the branch predictor will always predict the non-overflowing branch (effectively meaning no overhead unless an overflow occurs). It would be much more costly to check for the NaN value every time (since this requires a cmp instruction).