port/gen/ecvt.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*  Copyright (c) 1988 AT&T */
/*    All Rights Reserved   */

#pragma ident   "%Z%%M% %I% %E% SMI"

/*
 *  ecvt converts to decimal
 *  the number of digits is specified by ndigit
 *  decpt is set to the position of the decimal point
 *  sign is set to 0 for positive, 1 for negative
 *
 */

#pragma weak _ecvt = ecvt
#pragma weak _fcvt = fcvt

#include "lint.h"
#include <sys/types.h>
#include <values.h>
#include <nan.h>
#include <string.h>
#include "tsd.h"

#define NMAX    ((DSIGNIF * 3 + 19)/10) /* restrict max precision */
#define NDIG    80

static char *cvt(double, int, int *, int *, int);

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

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

static char *
cvt(double value, int ndigit, int *decpt, int *sign, int f_flag)
{
    char *buf = tsdalloc(_T_ECVT, NDIG, NULL);
    char *p = &buf[0], *p_last = &buf[ndigit];

    buf[0] = '\0';

    if (IsNANorINF(value)) {
        if (IsINF(value))  /* value is an INF, return "inf" */
            (void) strncpy(buf, "inf", NDIG);
        else /* value is a NaN, return "NaN" */
            (void) strncpy(buf, "nan", NDIG);

        return (buf);
    }

    if ((*sign = (value < 0.0)) != 0)
        value = -value;
    *decpt = 0;
    if (value != 0.0) {
/*
 * rescale to range [1.0, 10.0)
 * in binary for speed and to minimize error build-up
 * even for the IEEE standard with its high exponents,
 *  it's probably better for speed to just loop on them
 */
        static const struct s { double p10; int n; } s[] = {
            1e32,   32,
            1e16,   16,
            1e8,    8,
            1e4,    4,
            1e2,    2,
            1e1,    1,
        };
        const struct s *sp = s;

        ++*decpt;
        if (value >= 2.0 * MAXPOWTWO) /* can't be precisely integral */
            do {
                for (; value >= sp->p10; *decpt += sp->n)
                    value /= sp->p10;
            } while (sp++->n > 1);
        else if (value >= 10.0) { /* convert integer part separately */
            double pow10 = 10.0, powtemp;

            while ((powtemp = 10.0 * pow10) <= value)
                pow10 = powtemp;
            for (; ; pow10 /= 10.0) {
                int digit = value/pow10;
                *p++ = digit + '0';
                value -= digit * pow10;
                ++*decpt;
                if (pow10 <= 10.0)
                    break;
            }
        } else if (value < 1.0)
            do {
                for (; value * sp->p10 < 10.0; *decpt -= sp->n)
                    value *= sp->p10;
            } while (sp++->n > 1);
    }
    if (f_flag)
        p_last += *decpt;
    if (p_last >= buf) {
        if (p_last > &buf[NDIG - 2])
            p_last = &buf[NDIG - 2];
        for (; ; ++p) {
            if (value == 0 || p >= &buf[NMAX])
                *p = '0';
            else {
                int intx; /* intx in [0, 9] */
                *p = (intx = (int)value) + '0';
                value = 10.0 * (value - (double)intx);
            }
            if (p >= p_last) {
                p = p_last;
                break;
            }
        }
        if (*p >= '5') /* check rounding in last place + 1 */
            do {
                if (p == buf) { /* rollover from 99999... */
                    buf[0] = '1'; /* later digits are 0 */
                    ++*decpt;
                    if (f_flag)
                        ++p_last;
                    break;
                }
                *p = '0';
            } while (++*--p > '9'); /* propagate carries left */
        *p_last = '\0';
    }
    return (buf);
}