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
zero-value cells, so I multiplied the tabulated formula by 1 - (#1 < 0).
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