Two functions which I think could be beneficially added to l3fp without
straining its role as a kernel module (in the way that, say, the gamma
function would) are the signature function (sgn) and a unit step
function (Heaviside?  the difficulty is what value to assign at 0).
Given the numerical values assigned to true and false in l3fp, it is
easy to mimic these with simple inequalities (e.g. (#1 > 0)  (#1 < 0)
for sgn) but perhaps the functions should be there in the first place?
I found myself wanting these when considering a table of fp values where
it made sense to blank cells containing negative values which "got in
the way". The code creating the table contained the option of blanking
zerovalue cells, so I multiplied the tabulated formula by 1  (#1 < 0).
Andrew

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