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Sep 14, 2023 at 13:30 comment added Peter Cordes IIRC, -std=c++?? might change the FP-contract default, as opposed to the default -std=gnu++11 or whatever.
Sep 13, 2023 at 23:52 comment added Peter Cordes @G.Sliepen: GCC's default (without -ffast-math) is -ffp-contract=fast - contract a*b+c into FMA even if it's split across separate statements. (ISO C and C++ only allow contraction within one expression). Clang's default is IIRC -ffp-contract=no; unlike GCC, it supports on (within expressions but not across statements) as well as fast. -ffast-math sets fp-contract=fast, so yes probably good since I don't expect it to hurt precision in this case.
Sep 13, 2023 at 16:37 comment added G. Sliepen The compiler may in fact use fused multiply-accumulate instructions automatically in some cases. Using -ffast-math with GCC and Clang will allow the compiler to do more agressive math optimizations that might affect precision.
Sep 13, 2023 at 16:35 history edited G. Sliepen CC BY-SA 4.0
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Sep 13, 2023 at 16:12 history edited gnasher729 CC BY-SA 4.0
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Sep 13, 2023 at 16:05 history answered gnasher729 CC BY-SA 4.0