When does it make sense to use `Base.MultiplicativeInverses`

General Usage Performance
,
2

Right now you’re benchmarking with the constant 56. If it’s truly a constant, then that’ll probably always be equal or fastest (because LLVM does a similar transform on my platform!). Look ma, no divs:

julia> f(x) = div(x, 56)
f (generic function with 1 method)

julia> @code_native debuginfo=:none f(123123)
	.section	__TEXT,__text,regular,pure_instructions
	.build_version macos, 15, 0
	.globl	_julia_f_10054                  ; -- Begin function julia_f_10054
	.p2align	2
_julia_f_10054:                         ; @julia_f_10054
; Function Signature: f(Int64)
; %bb.0:                                ; %pass
	;DEBUG_VALUE: f:x <- $x0
	;DEBUG_VALUE: f:x <- $x0
	mov	x8, #18725
	movk	x8, #9362, lsl #16
	movk	x8, #37449, lsl #32
	movk	x8, #18724, lsl #48
	smulh	x8, x0, x8
	asr	x9, x8, #4
	add	x0, x9, x8, lsr #63
	ret
                                        ; -- End function
.subsections_via_symbols

You’d want to benchmark it without the constant propagation:

julia> @btime div.($un, 56); # constant!
  2.718 μs (3 allocations: 96.06 KiB)

julia> @btime div.($un, $(Ref(56))[]);
  6.267 μs (3 allocations: 96.06 KiB)

julia> @btime div.($un, $(Ref(MultiplicativeInverses.multiplicativeinverse(MultiplicativeInverses.unsigned(56))))[]);
  3.068 μs (3 allocations: 96.06 KiB)
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