/* $NetBSD: strpct.c,v 1.6 2025/05/13 04:50:45 rillig 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 <
[email protected]>, May 8, 1997
*/
#include <sys/cdefs.h>
__RCSID("$NetBSD: strpct.c,v 1.6 2025/05/13 04:50:45 rillig Exp $");
#include <limits.h>
#include <locale.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <util.h>
static uintmax_t
imax_abs(intmax_t x)
{
return x < 0 ? -(uintmax_t)x : (uintmax_t)x;
}
char *
strspct(char *buf, size_t bufsiz, intmax_t numerator, intmax_t denominator,
size_t digits)
{
if (bufsiz == 1)
buf[0] = '\0';
if (bufsiz <= 1)
return buf;
int sign = (numerator < 0) != (denominator < 0);
(void)strpct(buf + sign, bufsiz - sign, imax_abs(numerator),
imax_abs(denominator), digits);
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)
{
char *p = buf;
size_t n = bufsiz;
if (denominator == 0)
denominator = 1;
if (numerator >= denominator) {
size_t nw = snprintf(p, n, "%ju", numerator / denominator);
if (nw >= n)
return buf;
p += nw, n -= nw;
numerator %= denominator;
}
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 > 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;
}
