/*
 * 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   */

/*
 *      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);
}