Subversion Repositories planix.SVN

#include <math.h>
#include <stdlib.h>
double pow10(int);
#define NDIG    18
#define NFTOA   (NDIG+4)
/*
 * convert floating to ascii.  ftoa returns an integer e such that
 * f=g*10**e, with .1<=|g|<1 (e=0 when g==0) and puts an ascii
 * representation of g in the buffer pointed to by bp.  bp[0] will
 * be '+' or '-', and bp[1] to bp[NFTOA-2]
 * will be appropriate digits of g. bp[NFTOA-1] will be '\0'
 */
int ftoa(double f, char *bp){
        int e, e1, e2, i;
        double digit, g, p;
        if(f>=0) *bp++='+';
        else{
                f=-f;
                *bp++='-';
        }
        /* find e such that f==0 or 1<=f*pow10(e)<10, and set f=f*pow10(e) */
        if(f==0.) e=1;
        else{
                frexp(f, &e);
                e=-e*30103/100000;
                /* split in 2 pieces to guard against overflow in extreme cases */
                e1=e/2;
                e2=e-e1;
                p=f*pow10(e2);
                while((g=p*pow10(e1))<1.) e1++;
                while((g=p*pow10(e1))>=10.) --e1;
                e=e1+e2;
                f=g;
        }
        for(i=0;i!=NDIG;i++){
                f=modf(f, &digit)*10.;
                *bp++=digit+'0';
        }
        *bp='\0';
        return 1-e;
}