Re: [avr-libc-dev] [bug #23677] Request for cbrt() and strdup to be added to libc

[Russell Shaw]

Andy Hutchinson wrote:
> URL:
>   <http://savannah.nongnu.org/bugs/?23677>
>
>                  Summary: Request for cbrt() and strdup to be added to libc
>                  Project: AVR C Runtime Library
>             Submitted by: hutchinsonandy
>             Submitted on: Sunday 06/22/2008 at 21:51
>                 Category: Feature Request
>                 Severity: 3 - Normal
>                 Priority: 5 - Normal
>               Item Group: libc code
>                   Status: None
>         Percent Complete: 0%
>              Assigned to: None
>              Open/Closed: Open
>          Discussion Lock: Any
>                  Release: Any
>            Fixed Release: None
>
>     _______________________________________________________
>
> Details:
>
> It seems gcc testsuite assumes presence of widely available strdup() and
> cbrt() functions.
>
> strdup is a derivative of malloc
> cbrt is cubic root x^(1/3) 
>
> Here are some generic version that can be used as starter.
> I'm sure someone can trim them up a bit - or even convert to asm.
>
> Best version depends on how we built existing maths  functions.
>
> double cbrt(const double x)
>
> {
> return pow(x,1.0/3.0);
> }
>
> OR
>
> double cbrt(const double xx)
> {
>    double x= xx;
>    if  (x==0.0) /* log will fail, but answer is easy */
>       return 0.0;
>    else if  (x>0.0)
>        return(exp(log(x)/3.0));
>    else
>    x= -x;
>       return(exp(log(x)/3.0));
>   }

I *never* use straight fp equality in code (x==0.0 baaad).

http://c-faq.com/fp/fpequal.html
http://c-faq.com/fp/strangefp.html

> char *  strdup( const char *str)
> {
>        unsigned int len;
>        char *copy;
>        len = strlen(str) + 1;
>        copy = malloc(len);
>        if (!copy)
>                return (copy);
>        memcpy(copy, str, len);
>        return (copy);
> }

char *strdup(const char *str)
{
  if(!str) {
    return NULL;
  }
  return strdup(str);
}