Plus42 Equations, Preview Release

[Thomas Okken]

The HP-41C manual even mentions using SIGN to recognize strings. The 42S has the STR? function for that purpose, but still has SIGN return 1 for X=0 and 0 for strings, for backward compatibility with the 41.

In the equation compiler in Plus42, I made SGN() 17B-compatible by generating REAL? X≠0? SIGN. For complex arguments, SIGN works like UVEC, and this way, I was able to keep that behavior, while only working around the special case for real numbers equal to zero.