This can show up as material differences in output in the least significant bits in some cases.įor floating point intensive algorithms, these small discrepancies and edge cases will occasionally bubble to the surface as material differences in high-level code behavior. In practice, some alternative implementations of these instructions treat the underspecification as license to do just enough to clear the threshold of being technically compliant with the standard and no more.
The intent was to allow future microarchitectures to make small refinements in implementation as transistor budgets grew that might flip a bit in some high-precision edge cases. The underlying cause is that some floating point operations are underspecified, such that the behavior of some bits in the output of some operations are implementation defined.
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