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by burfog
2748 days ago
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Ah, but floating-point math is such fun! Here is how it might work... den is a tiny non-zero value in an 80-bit register. It gets spilled to a 64-bit slot on the stack, rounding it to zero, while another copy of it remains in an 80-bit register. The 80-bit version is compared against zero, and is non-zero. The 64-bit version, which is zero, gets used for the division. It is fully standards-compliant for a C compiler to do this. Some languages may specify otherwise, but often the behavior is unspecified or is implicitly the same as C. |
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However if you do use floating point, then the kind of dangers you point out make my point even stronger. You could conceivably embed the `calc_div` function in a larger system that knew about pre-validating for div0. But if you want to deal with all possible sources of FP weirdness when doing division, then you really need to concentrate it in the "division expert": i.e. have calc_div pre validate all that stuff, and have its caller accept that errors are a normal result.