add BigFloat fma and muladd

[nsajko]

No description provided.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.16 🎉

Comparison is base (86a502e) 88.80% compared to head (4c50cf9) 88.96%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
+ Coverage   88.80%   88.96%   +0.16%     
==========================================
  Files          22       22              
  Lines        2108     2121      +13     
==========================================
+ Hits         1872     1887      +15     
+ Misses        236      234       -2     

Impacted Files	Coverage Δ
src/implementations/BigFloat.jl	100.00% <100.00%> (ø)

... and 1 file with indirect coverage changes

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[blegat]

I prefer a few fixed tests for which we know muladd is different than fma than 100 random tests since it's difficult to reproduce

[nsajko]

Now the testing approach is to try a range of two-bit BigFloat values.

[blegat]

I'm not sure we want to do this because then muladd(x, y, z) would give a different result that operate!(muladd, x, y, z) wouldn't it ?

[nsajko]

Julia Base is being changed in the same direction, using the fused mpfr_fma for muladd: JuliaLang/julia#49401

[blegat]

Looks good to go then

[nsajko]

How to fix this:

julia> MA.operate!!(fma, 1, 1, 1)
ERROR: MethodError: no method matching operate(::typeof(fma), ::Int64, ::Int64, ::Int64)

Do I need to define an operate method for fma and muladd?

[nsajko]

The documentation actually leads me to believe that I shouldn't need to do anything, as immutable types should fall back to op(args...) automatically, no?

[blegat]

The documentation actually leads me to believe that I shouldn't need to do anything, as immutable types should fall back to op(args...) automatically, no?

Yes, operate(op, args...) should redirect to op(args...) like
but also make sure it returns a fresh copy which is what is done in

MutableArithmetics.jl/src/interface.jl

Lines 213 to 217 in 86a502e

	operate(::typeof(convert), ::Type{T}, x::T) where {T} = copy_if_mutable(x)
	function operate(::Union{typeof(+),typeof(*),typeof(gcd),typeof(lcm)}, x)
	return copy_if_mutable(x)
	end

You can add fma in

MutableArithmetics.jl/src/interface.jl

Lines 193 to 207 in 86a502e

	function operate(
	op::Union{
	typeof(+),
	typeof(*),
	AddSubMul,
	typeof(add_dot),
	typeof(gcd),
	typeof(lcm),
	},
	x,
	y,
	args::Vararg{Any,N},
	) where {N}
	return op(x, y, args...)
	end