sfstrtod.c   [plain text]

#include	"sfhdr.h"

/*	Convert a Sfdouble_t value represented in an ASCII format into
**	the internal Sfdouble_t representation.
**
**	Written by Kiem-Phong Vo.
*/

#define BATCH	(2*sizeof(int))	/* accumulate this many digits at a time */
#define IPART		0	/* doing integer part */
#define FPART		1	/* doing fractional part */
#define EPART		2	/* doing exponent part */

#if __STD_C
static Sfdouble_t sfpow10(reg int n)
#else
static Sfdouble_t sfpow10(n)
reg int	n;
#endif
{
	Sfdouble_t	dval;

	switch(n)
	{	case -3:	return .001;
		case -2:	return .01;
		case -1:	return .1;
		case  0:	return 1.;
		case  1:	return 10.;
		case  2:	return 100.;
		case  3:	return 1000.;
	}

	if(n < 0)
	{	dval = .0001;
		for(n += 4; n < 0; n += 1)
			dval /= 10.;
	}
	else
	{	dval = 10000.;
		for(n -= 4; n > 0; n -= 1)
			dval *= 10.;
	}

	return dval;
}

#if __STD_C
Sfdouble_t _sfstrtod(reg const char* s, char** retp)
#else
Sfdouble_t _sfstrtod(s,retp)
reg char*	s;	/* string to convert */
char**		retp;	/* to return the remainder of string */
#endif
{
	reg int		n, c, m;
	reg int		mode, fexp, sign, expsign;
	Sfdouble_t	dval;
#if _lib_locale
	int		decpoint = 0;
	SFSETLOCALE(&decpoint,NIL(int*));
#else
#define decpoint	'.'
#endif

	/* skip initial blanks */
	while(isspace(*s))
		++s;

	/* get the sign */
	if((sign = (*s == '-')) || *s == '+')
		s += 1;

	mode = IPART;
	fexp = expsign = 0;
	dval = 0.;
	while(*s)
	{	/* accumulate a handful of the digits */
		for(m = BATCH, n = 0; m > 0; --m, ++s)
		{	/* get and process a char */
			c = *s;
			if(isdigit(c))
				n = 10*n + (c - '0');
			else	break;
		}

		/* number of digits accumulated */
		m = BATCH-m;

		if(mode == IPART)
		{	/* doing the integer part */
			if(dval == 0.)
				dval = (Sfdouble_t)n;
			else	dval = dval*sfpow10(m) + (Sfdouble_t)n;
		}
		else if(mode == FPART)
		{	/* doing the fractional part */
			fexp -= m;
			if(n > 0)
				dval += n*sfpow10(fexp);
		}
		else if(n)
		{	/* doing the exponent part */
			if(expsign)
				n = -n;
			dval *= sfpow10(n);
		}

		if(!c)
			break;

		if(m < BATCH)
		{	/* detected a non-digit */
			if(c == decpoint)
			{	/* start the fractional part or no match */
				if(mode != IPART)
					break;
				mode = FPART;
				s += 1;
			}
			else if(c == 'e' || c == 'E')
			{	if(mode == EPART)
					break;
				mode = EPART;
				c = *++s;
				if((expsign = (c == '-')) || c == '+')
					s += 1;
			}
			else	break;
		}
	}

	if(retp)
		*retp = (char*)s;
	return sign ? -dval : dval;
}