Re: [cc65] IEEE vs nonstandard floats

Date view Thread view Subject view

From: David Holz (
Date: 2003-03-10 01:58:38

From: "Ullrich von Bassewitz" <>
> If you can prove in advance that a specific custom format is significantly
> faster than the IEEE format, I'm open for this suggestion. But I have to
> that I doubt this is the case.

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

> Here's another one: The standard specifies explicitly how the different
> situations should be handled, so it is easy to diagnose if there are
> with the implementation, and a user knows exactly what he can expect.

If those situations are met, but the binary representation isn't exactly
IEEE, it should still work, right?

> 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
> 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?

White Flame (aka David Holz)

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 01:54:19 CET