[racket-dev] [plt] Push #26002: master branch updated

On 01/01/2013 12:36 PM, mflatt at racket-lang.org wrote:
> 07d5a9e Matthew Flatt <mflatt at racket-lang.org> 2013-01-01 12:31
> :
> | fix `expt' on small negative number and large positive odd
> |
> | The pow() function apparently gets it wrong on some platforms.
> |
> | Closes PR 13391

Thanks, Matthew. I'm looking forward to getting bugged by DrDr less. :D

One question about the fix:

> src/racket/src/number.c
> ~~~~~~~~~~~~~~~~~~~~~~~
> --- OLD/src/racket/src/number.c
> +++ NEW/src/racket/src/number.c
> @@ -2729,7 +2729,16 @@ static double sch_pow(double x, double y)
>           return scheme_infinity_val;
>       }
>     } else {
> -    return protected_pow(x, y);
> +    double r;
> +    r = protected_pow(x, y);
> +    if ((r == 0.0) && !minus_zero_p(r)) {
> +      /* check large odd power of a small negative number,
> +         which some libraries get wrong for some reason */
> +      if ((x < 0) && (fmod(y, 2.0) == 1.0)) {
> +	r = scheme_floating_point_nzero;
> +      }
> +    }
> +    return r;
>     }
>   }
>   #endif

I looked into fixing this myself, and identified this as a spot to 
change. I also saw some JIT-looking stuff for `flexpt' that looked kind 
of like it was machine code, so I didn't try to fix it. Does this code 
you just changed get compiled during the build and then inlined by the JIT?

Neil ⊥