xref: /illumos-gate/usr/src/lib/libc/port/gen/ecvt.c (revision 1da57d551424de5a9d469760be7c4b4d4f10a755)
1 /*
2  * CDDL HEADER START
3  *
4  * The contents of this file are subject to the terms of the
5  * Common Development and Distribution License (the "License").
6  * You may not use this file except in compliance with the License.
7  *
8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
9  * or http://www.opensolaris.org/os/licensing.
10  * See the License for the specific language governing permissions
11  * and limitations under the License.
12  *
13  * When distributing Covered Code, include this CDDL HEADER in each
14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
15  * If applicable, add the following below this CDDL HEADER, with the
16  * fields enclosed by brackets "[]" replaced with your own identifying
17  * information: Portions Copyright [yyyy] [name of copyright owner]
18  *
19  * CDDL HEADER END
20  */
21 
22 /*
23  * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
24  * Use is subject to license terms.
25  */
26 
27 /*	Copyright (c) 1988 AT&T	*/
28 /*	  All Rights Reserved  	*/
29 
30 /*
31  *	ecvt converts to decimal
32  *	the number of digits is specified by ndigit
33  *	decpt is set to the position of the decimal point
34  *	sign is set to 0 for positive, 1 for negative
35  *
36  */
37 
38 #pragma weak _ecvt = ecvt
39 #pragma weak _fcvt = fcvt
40 
41 #include "lint.h"
42 #include <sys/types.h>
43 #include <values.h>
44 #include <nan.h>
45 #include <string.h>
46 #include "tsd.h"
47 
48 #define	NMAX	((DSIGNIF * 3 + 19)/10) /* restrict max precision */
49 #define	NDIG	80
50 
51 static char *cvt(double, int, int *, int *, int);
52 
53 char *
ecvt(double value,int ndigit,int * decpt,int * sign)54 ecvt(double value, int ndigit, int *decpt, int *sign)
55 {
56 	return (cvt(value, ndigit, decpt, sign, 0));
57 }
58 
59 char *
fcvt(double value,int ndigit,int * decpt,int * sign)60 fcvt(double value, int ndigit, int *decpt, int *sign)
61 {
62 	return (cvt(value, ndigit, decpt, sign, 1));
63 }
64 
65 static char *
cvt(double value,int ndigit,int * decpt,int * sign,int f_flag)66 cvt(double value, int ndigit, int *decpt, int *sign, int f_flag)
67 {
68 	char *buf = tsdalloc(_T_ECVT, NDIG, NULL);
69 	char *p = &buf[0], *p_last = &buf[ndigit];
70 
71 	buf[0] = '\0';
72 
73 	if (IsNANorINF(value)) {
74 		if (IsINF(value))  /* value is an INF, return "inf" */
75 			(void) strncpy(buf, "inf", NDIG);
76 		else /* value is a NaN, return "NaN" */
77 			(void) strncpy(buf, "nan", NDIG);
78 
79 		return (buf);
80 	}
81 
82 	if ((*sign = (value < 0.0)) != 0)
83 		value = -value;
84 	*decpt = 0;
85 	if (value != 0.0) {
86 /*
87  * rescale to range [1.0, 10.0)
88  * in binary for speed and to minimize error build-up
89  * even for the IEEE standard with its high exponents,
90  *  it's probably better for speed to just loop on them
91  */
92 		static const struct s { double p10; int n; } s[] = {
93 			1e32,	32,
94 			1e16,	16,
95 			1e8,	8,
96 			1e4,	4,
97 			1e2,	2,
98 			1e1,	1,
99 		};
100 		const struct s *sp = s;
101 
102 		++*decpt;
103 		if (value >= 2.0 * MAXPOWTWO) /* can't be precisely integral */
104 			do {
105 				for (; value >= sp->p10; *decpt += sp->n)
106 					value /= sp->p10;
107 			} while (sp++->n > 1);
108 		else if (value >= 10.0) { /* convert integer part separately */
109 			double pow10 = 10.0, powtemp;
110 
111 			while ((powtemp = 10.0 * pow10) <= value)
112 				pow10 = powtemp;
113 			for (; ; pow10 /= 10.0) {
114 				int digit = value/pow10;
115 				*p++ = digit + '0';
116 				value -= digit * pow10;
117 				++*decpt;
118 				if (pow10 <= 10.0)
119 					break;
120 			}
121 		} else if (value < 1.0)
122 			do {
123 				for (; value * sp->p10 < 10.0; *decpt -= sp->n)
124 					value *= sp->p10;
125 			} while (sp++->n > 1);
126 	}
127 	if (f_flag)
128 		p_last += *decpt;
129 	if (p_last >= buf) {
130 		if (p_last > &buf[NDIG - 2])
131 			p_last = &buf[NDIG - 2];
132 		for (; ; ++p) {
133 			if (value == 0 || p >= &buf[NMAX])
134 				*p = '0';
135 			else {
136 				int intx; /* intx in [0, 9] */
137 				*p = (intx = (int)value) + '0';
138 				value = 10.0 * (value - (double)intx);
139 			}
140 			if (p >= p_last) {
141 				p = p_last;
142 				break;
143 			}
144 		}
145 		if (*p >= '5') /* check rounding in last place + 1 */
146 			do {
147 				if (p == buf) { /* rollover from 99999... */
148 					buf[0] = '1'; /* later digits are 0 */
149 					++*decpt;
150 					if (f_flag)
151 						++p_last;
152 					break;
153 				}
154 				*p = '0';
155 			} while (++*--p > '9'); /* propagate carries left */
156 		*p_last = '\0';
157 	}
158 	return (buf);
159 }
160