Why NULL is 0

Stan Switzer sjs at spectral.ctt.bellcore.com
Thu Apr 7 22:52:43 AEST 1988


In reference to:
> > People (usually ;>) have no problem with the idea the while assigning a
> > zero to a float gives it the vaule 0.0, in most implementations the
> > float value does not have all bits set to zero.

And:
>   I do believe IEEE and Vax's version of float is a bit pattern
> consisting of all zeros.  So what are these implementations that don't
> use zero bit pattern?

The Honeywell 6000 Series and GE 625/635 machines represented NORMALIZED
float zero as o400000000000 (36 bits, msb ON).  This may date back to its
grand-uncle the 709.

BTW, all 0 bits WAS a float zero, but it wasn't normalized.  The results of
most float operations on unnormalized values was undefined.  I suspect that
additions and subtractions would lose precision in the process
of alligning the points.



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