From: Ullrich von Bassewitz (uz_at_musoftware.de)
Date: 2003-03-10 00:09:42
Hi! On Sun, Mar 09, 2003 at 01:46:07PM -0800, David Holz wrote: > What would cc65 gain by having IEEE standard FP notation as opposed to a > custom one that ran faster on the 6502? 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 admit that I doubt this is the case. A floating point number consists of two parts: Mantissa and exponent. The existing formats (yes, also the one used by Commodore) differ only in the representation of these two parts in the binary representation of the floating point number. The floating point routines need to work on both parts separately, so most of the difference is in separating the two components and joining them after the computation part is done. Maybe you can tell which concrete properties of the IEEE 32 bit format will lead to a slow implementation, so we can discuss the possible impact and alternatives. > The only one that I could think of > would be read/write compatibility with files that export floating point in > binary files which isn't that common. Here's another one: The standard specifies explicitly how the different situations should be handled, so it is easy to diagnose if there are problems with the implementation, and a user knows exactly what he can expect. > NaN and infinite also don't show up in Posix C programs without tossing a > SIGFPE signal do they? If not, they don't need to be handled with special > code which can tighten up the FP library and make it easier to implement. 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. I don't think that raising a signal is a good idea (my comment suggesting this was a joke) but the few bytes saved by not calling raise() are definitely not the reason for it. Regards Uz -- Ullrich von Bassewitz uz_at_musoftware.de ---------------------------------------------------------------------- To unsubscribe from the list send mail to majordomo_at_musoftware.de with the string "unsubscribe cc65" in the body(!) of the mail.
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