ack/lang/pc/libpc/cvt.c

#include "pc.h"

/* $Id$ */
#ifndef NOFLOAT

#if __STDC__
#include <float.h>
#else
#include <math.h>
#define DBL_MAX M_MAX_D
#endif

static char* cvt(double value, int ndigit, int* decpt, int* sign, int ecvtflag);

#define NDIGITS 128

char *_ecvt(double value, int ndigit, int *decpt, int *sign)
{
	return cvt(value, ndigit, decpt, sign, 1);
}

char *_fcvt(double value, int ndigit, int *decpt, int *sign)
{
	return cvt(value, ndigit, decpt, sign, 0);
}

static struct powers_of_10
{
	double pval;
	double rpval;
	int exp;
} p10[] = {
	1.0e32, 1.0e-32, 32,
	1.0e16, 1.0e-16, 16,
	1.0e8, 1.0e-8, 8,
	1.0e4, 1.0e-4, 4,
	1.0e2, 1.0e-2, 2,
	1.0e1, 1.0e-1, 1,
	1.0e0, 1.0e0, 0
};

static char* cvt(double value, int ndigit, int* decpt, int* sign, int ecvtflag)
{
	static char buf[NDIGITS + 1];
	register char* p = buf;
	register char* pe;

	if (ndigit < 0)
		ndigit = 0;
	if (ndigit > NDIGITS)
		ndigit = NDIGITS;
	pe = &buf[ndigit];
	buf[0] = '\0';

	*sign = 0;
	if (value < 0)
	{
		*sign = 1;
		value = -value;
	}

	*decpt = 0;
	if (value >= DBL_MAX)
	{
		value = DBL_MAX;
	}
	if (value != 0.0)
	{
		register struct powers_of_10* pp = &p10[0];

		if (value >= 10.0)
			do
			{
				while (value >= pp->pval)
				{
					value *= pp->rpval;
					*decpt += pp->exp;
				}
			} while ((++pp)->exp > 0);

		pp = &p10[0];
		if (value < 1.0)
			do
			{
				while (value * pp->pval < 10.0)
				{
					value *= pp->pval;
					*decpt -= pp->exp;
				}
			} while ((++pp)->exp > 0);

		(*decpt)++; /* because now value in [1.0, 10.0) */
	}
	if (!ecvtflag)
	{
		/* for fcvt() we need ndigit digits behind the dot */
		pe += *decpt;
		if (pe > &buf[NDIGITS])
			pe = &buf[NDIGITS];
	}
	while (p <= pe)
	{
		*p++ = (int)value + '0';
		value = 10.0 * (value - (int)value);
	}
	if (pe >= buf)
	{
		p = pe;
		*p += 5; /* round of at the end */
		while (*p > '9')
		{
			*p = '0';
			if (p > buf)
				++*--p;
			else
			{
				*p = '1';
				++*decpt;
				if (!ecvtflag)
				{
					/* maybe add another digit at the end,
					   because the point was shifted right
					*/
					if (pe > buf)
						*pe = '0';
					pe++;
				}
			}
		}
		*pe = '\0';
	}
	return buf;
}
#endif