PSA: floating-point arithmetic

[simonbyrne]

@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).