/*      $NetBSD: strpct.c,v 1.7 2025/12/14 16:28:05 kre Exp $   */

/*-
 * Copyright (c) 1998, 2025 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Erik E. Fair and Roland Illig.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Calculate a percentage without resorting to floating point
 * and return a pointer to a string
 *
 * "digits" is the number of digits past the decimal place you want
 * (zero being the straight percentage with no decimals)
 *
 * Erik E. Fair <fair@clock.org>, May 8, 1997
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: strpct.c,v 1.7 2025/12/14 16:28:05 kre Exp $");

#include <limits.h>
#include <locale.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <string.h>
#include <util.h>

static uintmax_t
imax_abs(intmax_t x)
{

        return x < 0 ? -(uintmax_t)x : (uintmax_t)x;
}

static  uint32_t _round_ = STRPCT_RTZ;  /* Historic method */
/*
 * Set the rounding mode used by the strpct() and strspct() functions
 */
uint32_t
strpct_round(uint32_t mode)
{
        uint32_t oldmode = _round_;

        switch (mode) {
        case STRPCT_RTN:
        case STRPCT_RTZ:
        case STRPCT_RAZ:
        case STRPCT_RTI:
        case STRPCT_RAI:
                _round_ = mode;
                break;
        }

        return oldmode;
}

char *
strspct(char *buf, size_t bufsiz, intmax_t numerator, intmax_t denominator,
    size_t digits)
{
        return
            strspct_r(buf, bufsiz, numerator, denominator, digits, _round_);
}

char *
strspct_r(char *buf, size_t bufsiz, intmax_t numerator, intmax_t denominator,
    size_t digits, uint32_t round)
{
        int sign;

        if (bufsiz == 1)
                buf[0] = '\0';
        if (bufsiz <= 1)
                return buf;

        sign = (numerator < 0) != (denominator < 0);
        if (sign && (round == STRPCT_RTI || round == STRPCT_RAI))
                round ^= (STRPCT_RTI ^ STRPCT_RAI);

        (void)strpct_r(buf + sign, bufsiz - sign, imax_abs(numerator),
            imax_abs(denominator), digits, round);
        if (sign)
                *buf = '-';
        return buf;
}

typedef struct {
        unsigned hi;
        uintmax_t lo;
} bignum;

static bignum
bignum_plus(bignum x, bignum y)
{
        x.hi += y.hi;
        if (x.lo + y.lo < x.lo)
                x.hi++;
        x.lo += y.lo;
        return x;
}

static bignum
bignum_minus_u(bignum x, uintmax_t y)
{
        if (x.lo - y > x.lo)
                x.hi--;
        x.lo -= y;
        return x;
}

static bignum
bignum_times_10(bignum x)
{
        bignum x2 = bignum_plus(x, x);
        bignum x4 = bignum_plus(x2, x2);
        bignum x8 = bignum_plus(x4, x4);
        return bignum_plus(x2, x8);
}

static bool
bignum_ge_u(bignum x, uintmax_t y)
{
        return x.hi > 0 || x.lo >= y;
}

char *
strpct(char *buf, size_t bufsiz, uintmax_t numerator, uintmax_t denominator,
    size_t digits)
{
        return
            strpct_r(buf, bufsiz, numerator, denominator, digits, _round_);
}

char *
strpct_r(char *buf, size_t bufsiz, uintmax_t numerator, uintmax_t denominator,
    size_t digits, uint32_t round)
{
        char *p = buf;
        size_t n = bufsiz;

        if (denominator == 0)
                denominator = 1;

        if (numerator >= denominator) {
                uintmax_t quotient = numerator / denominator;
                uintmax_t remainder = numerator - (quotient * denominator);
                size_t nw = snprintf(p, n, "%ju", quotient);

                if (nw >= n) {
                        /*
                         * We have only unsigned numbers here, so
                         * rounding away from zero and towards Inf are the same
                         * Sim rounding towards zero, and away from Inf
                         * (away from Inf is the same thing as towards -Inf)
                         */
                        switch (round & 3) {
                                /* round towards 0, round towards -Inf */
                        case STRPCT_RTZ:
                                        /* truncate; do nothing */
                                break;

                                /* round to nearest (0.5 always away) */
                        case STRPCT_RTN:
                        default:
                                if (remainder * 2 < denominator)
                                        break;
                                /* FALLTHROUGH */

                                /* round away from 0, or towards Inf */
                        case STRPCT_RAZ:
                                if (remainder == 0)
                                        break;

                                (void)snprintf(p, n, "%ju", quotient + 1);
                                break;
                        }
                        return buf;
                }
                p += nw, n -= nw;
                numerator = remainder;
        }

        if (n < 2) {
                if (n != 0)
                        buf[0] = '\0';
                return buf;
        }

        bignum num = { 0, numerator };
        for (size_t i = 0; i < 2 + digits; i++) {
                num = bignum_times_10(num);

                unsigned digit = 0;
                for (; bignum_ge_u(num, denominator); digit++)
                        num = bignum_minus_u(num, denominator);

                if (i == 1 + digits || n <= 2) {
                        /*
                         * This will be the last digit, so round it.
                         * nb: all values here are non-negative
                         */
                        if (!(round & 1)) {                   /* round down  */
                            if (round != 0 ? bignum_ge_u(num, 1) :  /* up   */
                                bignum_ge_u(bignum_plus(num, num),  /* rtn */
                                                         denominator)) {
                                if (digit < 9) {
                                    digit++;
                                } else {
                                    if (n == 0)
                                        break;
                                    digit = 0;
                                    if (p == buf) {
                                        *p++ = '1';
                                        n--;
                                    } else for (char *q = p; --q >= buf; ) {
                                        if (*q < '0' || *q > '9') /* the '.' */
                                                continue;
                                        if (*q == '9') {
                                            *q = '0';
                                            if (q == buf) {
                                                if ((size_t)(p - buf) >=
                                                    bufsiz - 1)
                                                        p--;
                                                memmove(q+1,q,(size_t)(p-buf));
                                                *q = '1';
                                                p++;
                                                n--;
                                                break;
                                            }
                                        } else {
                                            (*q)++;
                                            break;
                                        }
                                    }
                                }
                            }
                        }
                }

                if (i > 0 || p > buf || digit > 0) {
                        if (n >= 2)
                                *p++ = '0' + digit, n--;
                        if (n >= 1)
                                *p = '\0';
                        if (n <= 1)
                                break;
                }

                if (i == 1 && digits > 0) {
                        const char *dp = localeconv()->decimal_point;
                        while (*dp != '\0' && n >= 2)
                                *p++ = *dp++, n--;
                        if (n >= 1)
                                *p = '\0';
                        if (n <= 1)
                                break;
                }
        }
        return buf;
}