cvt.c

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/* $Header: /opt/proj/minix/cvsroot/src/lib/ack/libp/cvt.c,v 1.1 2005/10/10 15:27:46 beng Exp $ */
#ifndef NOFLOAT

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

static char *cvt();
#define NDIGITS 128

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

char *
_fcvt(value, ndigit, decpt, sign)
        double value;
        int ndigit, *decpt, *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(value, ndigit, decpt, sign, ecvtflag)
        double value;
        int ndigit, *decpt, *sign;
{
        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

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