Re: Inexact floating-point compare

[EMAIL PROTECTED] wrote:
> Terje Mathisen <[EMAIL PROTECTED]> wrote:
> : 
> : The easiest method would seem to be a subtract, scale, add and compare:
> : 
> : double inexact_compare(double a, double b, int bits_to_skip)
> : {
> :   // First the the regular difference:
> :   double diff = b - a;
> : 
> :   // Shift this difference down by the number of bits to ignore:
> :   double scaled_diff = diff / ((double) (2 << bits_to_skip));
> :
>
> This does not work for floating point..... or am I missing something 
> obvious?

Well, it does work (modulo having a shift which is smaller than the 
bitsoze of an integer), but the casting to double of the integer shift 
result is pretty non-optimal, as is the fp division that follows.

As I wrote in my post, this was only for illustration, a useful 
implementation would either use a fp scale operation or a lookup table 
to generate a suitable shifting multiplier.

Terje

--
- <[EMAIL PROTECTED]>
"almost all programming can be viewed as an exercise in caching"