# PSA: floating-point arithmetic

**URL:** <https://discourse.julialang.org/t/psa-floating-point-arithmetic/8678>\
**Category:** Offtopic\
**Created:** [January 29, 2018, 7:56pm UTC](https://discourse.julialang.org/t/psa-floating-point-arithmetic/8678 "2018-01-29T19:56:38Z")\
**Posts on this page:** 1\
**Showing post:** 8

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**Author:** ![simonbyrne](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/simonbyrne/32/19_2.png) [@simonbyrne](https://discourse.julialang.org/u/simonbyrne)\
**Post date:** [January 31, 2018, 10:10pm UTC](https://discourse.julialang.org/t/psa-floating-point-arithmetic/8678/8 "2018-01-31T22:10:15Z")

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> [@foobar\_lv2](#):
>
> I have never seen julia emit the 80 bit stuff; I guess it is never used, but I’d be happy about reassurance.

No, on x86 we only use SSE instructions (80-bit floats are only available with x87 instructions).

Note there are still some ways you might get non-deterministic results:

- BLAS or LAPACK operations
- `@fastmath`: which lets the compiler do a _lot_ of manipulations
- `@simd`: which allows re-association of arithmetic operations to exploit SIMD operations.
- `muladd`: allows use of either `a*b+c` or `fma(a,b,c)` depending on which is faster. This is a tricky one, as we’re increasingly making use of it (such as the recent libm work).

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