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;

}