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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