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strpct.c revision 1.6 
      1 /*	$NetBSD: strpct.c,v 1.6 2025/05/13 04:50:45 rillig Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1998, 2025 The NetBSD Foundation, Inc.
      5  * All rights reserved.
      6  *
      7  * This code is derived from software contributed to The NetBSD Foundation
      8  * by Erik E. Fair and Roland Illig.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  *
     19  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     20  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     21  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     22  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     23  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     24  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     25  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     26  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     27  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     28  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     29  * POSSIBILITY OF SUCH DAMAGE.
     30  */
     31 
     32 /*
     33  * Calculate a percentage without resorting to floating point
     34  * and return a pointer to a string
     35  *
     36  * "digits" is the number of digits past the decimal place you want
     37  * (zero being the straight percentage with no decimals)
     38  *
     39  * Erik E. Fair <fair (at) clock.org>, May 8, 1997
     40  */
     41 
     42 #include <sys/cdefs.h>
     43 __RCSID("$NetBSD: strpct.c,v 1.6 2025/05/13 04:50:45 rillig Exp $");
     44 
     45 #include <limits.h>
     46 #include <locale.h>
     47 #include <stdbool.h>
     48 #include <stdint.h>
     49 #include <stdio.h>
     50 #include <util.h>
     51 
     52 static uintmax_t
     53 imax_abs(intmax_t x)
     54 {
     55 
     56 	return x < 0 ? -(uintmax_t)x : (uintmax_t)x;
     57 }
     58 
     59 char *
     60 strspct(char *buf, size_t bufsiz, intmax_t numerator, intmax_t denominator,
     61     size_t digits)
     62 {
     63 
     64 	if (bufsiz == 1)
     65 		buf[0] = '\0';
     66 	if (bufsiz <= 1)
     67 		return buf;
     68 
     69 	int sign = (numerator < 0) != (denominator < 0);
     70 	(void)strpct(buf + sign, bufsiz - sign, imax_abs(numerator),
     71 	    imax_abs(denominator), digits);
     72 	if (sign)
     73 		*buf = '-';
     74 	return buf;
     75 }
     76 
     77 typedef struct {
     78 	unsigned hi;
     79 	uintmax_t lo;
     80 } bignum;
     81 
     82 static bignum
     83 bignum_plus(bignum x, bignum y)
     84 {
     85 	x.hi += y.hi;
     86 	if (x.lo + y.lo < x.lo)
     87 		x.hi++;
     88 	x.lo += y.lo;
     89 	return x;
     90 }
     91 
     92 static bignum
     93 bignum_minus_u(bignum x, uintmax_t y)
     94 {
     95 	if (x.lo - y > x.lo)
     96 		x.hi--;
     97 	x.lo -= y;
     98 	return x;
     99 }
    100 
    101 static bignum
    102 bignum_times_10(bignum x)
    103 {
    104 	bignum x2 = bignum_plus(x, x);
    105 	bignum x4 = bignum_plus(x2, x2);
    106 	bignum x8 = bignum_plus(x4, x4);
    107 	return bignum_plus(x2, x8);
    108 }
    109 
    110 static bool
    111 bignum_ge_u(bignum x, uintmax_t y)
    112 {
    113 	return x.hi > 0 || x.lo >= y;
    114 }
    115 
    116 char *
    117 strpct(char *buf, size_t bufsiz, uintmax_t numerator, uintmax_t denominator,
    118     size_t digits)
    119 {
    120 	char *p = buf;
    121 	size_t n = bufsiz;
    122 
    123 	if (denominator == 0)
    124 		denominator = 1;
    125 
    126 	if (numerator >= denominator) {
    127 		size_t nw = snprintf(p, n, "%ju", numerator / denominator);
    128 		if (nw >= n)
    129 			return buf;
    130 		p += nw, n -= nw;
    131 		numerator %= denominator;
    132 	}
    133 
    134 	bignum num = { 0, numerator };
    135 	for (size_t i = 0; i < 2 + digits; i++) {
    136 		num = bignum_times_10(num);
    137 
    138 		unsigned digit = 0;
    139 		for (; bignum_ge_u(num, denominator); digit++)
    140 			num = bignum_minus_u(num, denominator);
    141 
    142 		if (i > 0 || p > buf || digit > 0) {
    143 			if (n >= 2)
    144 				*p++ = '0' + digit, n--;
    145 			if (n >= 1)
    146 				*p = '\0';
    147 			if (n <= 1)
    148 				break;
    149 		}
    150 
    151 		if (i == 1 && digits > 0) {
    152 			const char *dp = localeconv()->decimal_point;
    153 			while (*dp != '\0' && n >= 2)
    154 				*p++ = *dp++, n--;
    155 			if (n >= 1)
    156 				*p = '\0';
    157 			if (n <= 1)
    158 				break;
    159 		}
    160 	}
    161 	return buf;
    162 }
    163