Marcel Kilgus writes: > > In internal format, Exponent . Mantissa: > > > -1 = $800 . $C0000000 > > -1 + 0 = $801 . $80000000 > > > which can be a flaming nuisance! > > You got the mantissas and exponents mixed up, $800 $80000000 is "-1" > and $801 $C0000000 is "-1" but not your two. As Robert wrote this is a
Just checking whether everyone was paying attention. You obviously were ;) > question of normalisation, however, QDOS FP values don't have the > implied "1." he mentions (this is for example found in the IEEE > standard, except the 80bit one which is a bit special in this > respect). As far as I know normalisation is not required for QDOS FP > values. A "bit" special, eh. Nice pun. <> > Example: Epsilon = 0.000000001 > IF (a - b) < Epsilon THEN PRINT "They are equal". > > In SuperBasic I believe this technique is already implied when using > the "=" operator. But you cannot just compare the bytes of the two The S*Basic "==" (double equals) works in this case. > values (e.g. in assembler) because of the different representations a > value can have (there's some rounding going on almost every time one > uses FP). So that means a hefty re-write of my old assembler float comparison routine ;( And anyone using SNG's diy stuff, based on the same assumptions, is in for a surprise too. I just checked.) > > Is this a bug? > > Point of view, I'd say no. The original SMSQ/E routines give the same > result for both -1 and -1+0, it's the PC FPU (or the IEEE->QDOS > translation) that gives something different on QPC. I could probably > do some normalisation, which could solve your problem in THIS case, > but other than that... Bug or no bug, it is a compatibility issue, and one that may trash existing programs. Are there any other likely pitfalls? Thanks for your comprehensive reply! Per
