At Fri, 12 Mar 2004 09:18:41 +0100, Vincent Lefevre wrote: > On 2004-03-12 15:49:08 +0900, GOTO Masanori wrote: > > Could you provide me more information? > > > > - Which merit should we use them? > > It is sometimes absolutely necessary to have double-precision > rounding: some algorithms (e.g. to compute with higher precision) > need that, ditto for some standards (Java, XPath). One of the goals > of the IEEE-754 standard is to get reproducible results on various > architectures; so it would be more sensible to have double-precision > rounding in most cases (in fact, I've been told that this was the > case under MS Windows, but I didn't check). Extended precision was > created to allow to implement standard math functions (exp, log, > sin, cos, and so on) easily, by using the arithmetic operations. > > > - n752.htm has only above explanation. Where can I get more info? > > Concerning the specification, isn't this sufficient? Concerning the > implementation, I suppose that this would merely be a wrapper around > fpu_control.h macros. I probably can write that if you want. > > Fred Tydeman has also written a file fenvx87.h you can download from > his FTP site <ftp://jump.net/pub/tybor/>, as an example. > > > - Do x86 processors have this kind of functions? > > These processors have such control of the dynamic precision modes.
Thanks for your detailed explanation, I understand this is about manipulating wrapper function of x87 precious control field. The similar symbol is already defined in fpu_control.h like _FPU_EXTENDED and so, on i386/adm64/m68k/sparc. > > - Why was this dropped? > > According to Fred Tydeman: "I believe because it only makes sense on > those machines with dynamic rounding precision (which is not mandated > by IEEE-754) and there are many machines with static precision." > > However, you should note that: > > * This wouldn't hurt on machines with static precision. In practice, > the goal would be to change the precision to the double precision > in every case (nothing to do on machines with static precision). > > * There are also machines with static rounding modes (e.g. ARM > processors, at least early ones -- those with a floating-point > coprocessor; and possibly future processors, depending on the > revision of the IEEE-754 standard); but the functions/macros > to set/get the dynamic rounding mode haven't been dropped. I understand this is sometimes useful when a user want to change the precision of FPU. But, the problem is it's extended function, not standard. soft-fp in glibc uses EXTENDED, and don't recommend SINGLE. I found recent Solaris on x86 only defines it. Is this function future-rock? Regards, -- gotom -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
