libc6 uses long double for math constants

[Enrique Zanardi <ezanardi@noah.dfis.ull.es>]

This one may bite many others:

The file /usr/include/math.h defines a few math contants like
M_PI, M_E or M_LN2 to name a few. 

The problem is, in libc5 those were defined as floats: 

"...
#ifndef M_PI
#define M_PI        3.14159265358979323846      /* pi */
#endif
..."

but in libc6, if using GCC (or any standard C compiler), those are defined
as long double floats:

"...
#ifdef __USE_BSD
...
#define M_PI            _Mldbl(3.14159265358979323846)  /* pi */
...
/* Our constants might specify more precision than `double' can represent.
   Use `long double' constants in standard and GNU C, where they are
   supported and the cast to `double'.  */
#if __STDC__ - 0 || __GNUC__ - 0
#define _Mldbl(x) x##L
#else   /* Traditional C.  */
#define _Mldbl(x) x
#endif  /* Standard or GNU C.  */

#endif
..."

So, if you do some calculations in your function calls, like:

#include <math.h>
#include <stdio.h>

#define RADtoDEG(a)     ((a) * 180.0 / M_PI)

void main(){
    double a;

    a=3.14159265;
    printf ("%g rad = %g deg\n",a,RADtoDEG(a));
    /*  Look mama, no casting ----^^^^^^^^^^^ */              
}

your programs, that were working fine compiled with libc5, will go
berserk as soon as you recompile them with libc6.

-- 
Enrique Zanardi					ezanardi@noah.dfis.ull.es
Dpto. Fisica Fundamental y Experimental
Univ. de La Laguna


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