Re: [boost] Math constants for naive and gurus? - which constants do you want?

From: Greg Colvin (gcolvin_at_[hidden])
Date: 2001-10-23 20:12:15

From: Greg Colvin <gcolvin_at_[hidden]>
> > Many thanks for your work on this.  Looks promising, but may
> > be worth also producing the plain const double/float/long double files
> > as well for the time being at least?
> > 
> > Paul
> 
> The plain const was actually less efficient for some platforms.
> 
> The only problems I see with the template function approach is
> the extra typing:
> 
>     v = pi
> 
> is certainly easier than
> 
>     v = constant<pi_tag,double>
> 
> but it is not amenable to more precise implementations.
> 
> How about a compromise:
> 
>     v = pi<double>()
> 
> and so on for all the other constants?  I think this can be
> made to work with even the most brain-dead compilers.

The following little test

    template<typename Type> inline Type pi() {
       return (Type)3.1415926535897932384626433832795028841972L;
    }
    extern int f(float&,double&,long double&);
    int pi_test() {
       float pi_float = pi<float>();
       double pi_double = pi<double>();
       long double pi_long_double = pi<long double>();
       return f(pi_float,pi_double,pi_long_double);
    }

produces the following Sparc code with Sun's latest compiler

    ___const_seg_900000101:
         .word   1078530011
         .align  8
         .word   1074340347,1413754136
         .word   1073779231,-1253817647,-2073458292,-9883
         .type   ___const_seg_900000101,1
         .size   ___const_seg_900000101,(.-___const_seg_9
         .align  4
         .global __1cHpi_test6F_i_
    __1cHpi_test6F_i_:
         save    %sp,-128,%sp

    !   float pi_float = pi<float>();
    !   double pi_double = pi<double>();
    !   long double pi_long_double = pi<long double>();

         sethi   %hi(___const_seg_900000101+16),%g1
         sethi   %hi(___const_seg_900000101),%g2
         ld      [%g1+%lo(___const_seg_900000101+16)],%g3
         add     %g1,%lo(___const_seg_900000101+16),%g4
         sethi   %hi(___const_seg_900000101+8),%g1
         ld      [%g4+4],%o3

    !   return f(pi_float,pi_double,pi_long_double);

         add     %fp,-4,%o0
         add     %fp,-16,%o1
         ldd     [%g1+%lo(___const_seg_900000101+8)],%f2
         add     %fp,-32,%o2
         ld      [%g4+8],%o4
         ld      [%g2+%lo(___const_seg_900000101)],%f0
         st      %g3,[%fp-32]
         st      %o3,[%fp-28]
         std     %f2,[%fp-16]
         ld      [%g4+12],%o5
         st      %f0,[%fp-4]
         st      %o4,[%fp-24]
         call    __1cBf6FrfrdrD_i_       ! params =  %o0 
         st      %o5,[%fp-20]
         ret     ! Result =  %i0
         restore %g0,%o0,%o0
         .type   __1cHpi_test6F_i_,2
         .size   __1cHpi_test6F_i_,(.-__1cHpi_test6F_i_)