Re: [cc65] IEEE vs nonstandard floats

Date view Thread view Subject view

From: Spiro Trikaliotis (
Date: 2003-03-10 10:21:27


David Holz wrote:

> What I meant is if there's a good 6502 FP library available that doesn't use
> exactly the IEEE binary representation.  For instance, my math lib that I've
> been messing around with for some time has the exponent as the number of
> bytes (instead of bits) to shift, and I normalize the highest mantissa byte
> to non-zero instead of having the implied "1" hanging off the end.  Saves a
> load of bit-shifting, but I add another byte onto the mantissa to maintain
> precision.  Plus, I haven't finished it so it's as of yet unproven, but I
> think it's got good potential as a different, faster way of doing FP on the
> 6502.

Yes, it is faster, but it is not binary FP anymore, this is hexadecimal FP.
And this has some severe disadvantages which I don't remember anymore. For 
those interested, have a look at Donald E. Knuth: TAOCP, Vol. 2: "Seminumerical 

> > The C standard does not require fp math functions to raise a signal on an
> > error condition. But it requires that the a math function returns an
> > implementation defined value, so these error conditions have to be
> > detected
> > and handled in some way.
> Right, so SIGFPE is Posix or somesuch, but you can implement any error
> mechanism you want (well, besides crashing ;) ) and still be C compliant?

yes, an error mechanism could even be "doing nothing".


To unsubscribe from the list send mail to with
the string "unsubscribe cc65" in the body(!) of the mail.

Date view Thread view Subject view

This archive was generated by hypermail 2.1.3 : 2003-03-10 10:19:20 CET