Re: Different printed output with floating point numbers

From: Russell Browne (
Date: Wed Mar 07 2001 - 18:10:31 GMT

As William Dowling points out:

> "1.3" and "1.29999995232" are two ASCII decimal representations of the
> same underlying 32-bit binary floating point value, that differ only
> in how much they are lying about the precision (32 bits) of the
> underlying value. (There are infinitely many such ASCII decimal
> representationas -- add as many mor 9's as you like.)

In fact, if you try the following program:

   int main()
       float foo = 1.3;
       double food = foo;
       return 0;

Run under ups, stop on the return and display foo and food, you see 

      main                                           bob.c:5
	       float <foo>                        1.3
	       double <food>                      1.29999995232

The problem Bob reports arises in the C interpreter, where there is a
conversion of intermediate float results to doubles.


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