[VA] "Introducing APRIL !" microchallenge

[Valentin Albillo]

  
Hi, all,

Let me introduce APRIL (Arithmetic Problem Recently Identified Locally), which is an arithmetic problem I recently identified locally while using some vintage HP calcs. My identification might be recent but the problem itself has been lurking unnoticed for 40+ years, AFAIK.

To wit, there's a purely arithmetic operation that produces a result when executed in one series ("Spice": HP-33E/C, HP-34C ...) and a different one when executed in another series ("Nut" CPUs: HP-41, HP-10C, HP-15C ...). The term "arithmetic operation" does include √x but excludes all transcendental functions, statistics-related ones, y^x, ->H.MS and ->HR.

I thought that by the early '80s all basic arithmetic firmware would be thoroughly debugged and essentially cast in stone but it seems it wasn't, which hit me hard when this purely arithmetic program of mine (dealing with values in the range [0.1 ... 1500]) would produce very different results when run on said HP calcs, so it took me some sleuthing to isolate the culprit.

Now that you know beyond a shadow of a doubt that there's one, see if you can find such a faulty arithmetic operation. Unless this is another elaborate April Fools' Day joke !!.

V.