xexpx(z)

[cossio]

I frequently encounter the function xexpx(z) = z * exp(z), with the caveat that xexpx(-Inf) == 0. Thus xexpx(z) = xlogx(exp(z)), but computing it directly is faster because it avoids a superfluous log call and might prevent intermediate overflows..

Can we consider adding the definition:

xexpx(x::Real) = x == -Inf ? exp(x) : x * exp(x)

[tpapp]

JuliaStats/StatsFuns.jl#58 was just closed, but porting it here is welcome.