Re: [Mingw-users] RE: The value of pi

[<dan...@ya...>]

And this brings us back to the original post that started this thread. 
Should mingw math.h header define PI as a manifest constant.

This example, IMO, indicates the value of having a constant defined as a
macro, rather than a function.

If we do this:
 #define PI 3.1415926535897932

or even this (ugh)

/* in library */
double __d; 
unsigned short __s[4];
} __PI = { __s:{0x2d18,0x5444,0x21fb,0x4009}}; 

/* in header */
extern const double __PI;
#define PI __PI;

we get the same value for PI no matter how it is used.   A "constant" whose
precision is dependent on surrounding code is not much good to me.  I would
rather have less precision that I know about rather than try to figure out
why I get different answers with different levels of optimisation.

My two cents.  I think we should define PI and friends as constants (the
simple way)  Having a mingw PI the same as an i386 glibc (or newlib or
cephes) PI is a good thing.

Danny

--- Wu Yongwei <ad...@ne...> wrote: > I found a way to simulate the
inline sin of MSVC:
> 
> #include <stdio.h>
> //#include <math.h>
> #include "pi.h"
> 
> #define sin(x) \
>     ({ double v; __asm ("fsin" : "=&t" (v) : "0" (x)); v; })
> 
> int main()
> {
>     //printf("%.16g\n", 3 * pi() / 8.0);
>     printf("%.16g\n", sin(pi()));
>     printf("%.16g\n", sin(3.1415926535897932));
>     return 0;
> }
> 
> -5.421010862427522e-020
> 1.224606353822377e-016
> 
> However, uncomment the first printf and you will not see the improved
> result
> of sin(pi) because GCC stored pi in memory already. I really don't like
> this. I am now assured that a floating-point-intensive application should
> use MSVC indeed.
> 
> (BTW, vim seems to think the strange definition of sin is invalid.)
> 
> Best regards,
> 
> Wu Yongwei
> 
> 
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