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strpct.c revision 1.4 
      1 /* $NetBSD: strpct.c,v 1.4 2025/05/02 20:00:45 rillig Exp $ */
      2 
      3 /*-
      4  * Copyright (c) 1998 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
      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 1.4 2025/05/02 20:00:45 rillig Exp $");
     44 
     45 #include <stdint.h>
     46 #include <locale.h>
     47 #include <limits.h>
     48 #include <stdio.h>
     49 #include <errno.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 	switch (bufsiz) {
     65 	case 1:
     66 		*buf = '\0';
     67 		/*FALLTHROUGH*/
     68 	case 0:
     69 		return buf;
     70 	default:
     71 		break;
     72 	}
     73 
     74 	int sign = (numerator < 0) != (denominator < 0) ? 1 : 0;
     75 	(void)strpct(buf + sign, bufsiz - sign, imax_abs(numerator),
     76 	    imax_abs(denominator), digits);
     77 	if (sign)
     78 		*buf = '-';
     79 	return buf;
     80 }
     81 
     82 char *
     83 strpct(char *buf, size_t bufsiz, uintmax_t numerator, uintmax_t denominator,
     84     size_t digits)
     85 {
     86 	uintmax_t factor, result;
     87 	size_t u;
     88 
     89 	factor = 100;
     90 	for (u = 0; u < digits; u++) {
     91 		/* watch out for overflow! */
     92 		if (factor < (UINTMAX_MAX / 10))
     93 			factor *= 10;
     94 		else
     95 			break;
     96 	}
     97 
     98 	/* watch out for overflow! */
     99 	if (numerator < (UINTMAX_MAX / factor))
    100 		numerator *= factor;
    101 	else {
    102 		/* toss some of the bits of lesser significance */
    103 		denominator /= factor;
    104 	}
    105 
    106 	if (denominator == 0)
    107 		denominator = 1;
    108 
    109 	result = numerator / denominator;
    110 
    111 	if (digits == 0)
    112 		(void)snprintf(buf, bufsiz, "%ju", result);
    113 	else {
    114 		factor /= 100;		/* undo initialization */
    115 
    116 		(void)snprintf(buf, bufsiz, "%ju%s%0*ju",
    117 		    result / factor, localeconv()->decimal_point, (int)u,
    118 		    result % factor);
    119 	}
    120 
    121 	return buf;
    122 }
    123