xref: /freebsd/lib/libc/gdtoa/_ldtoa.c (revision c66ec88fed842fbaad62c30d510644ceb7bd2d71)
1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3  *
4  * Copyright (c) 2003 David Schultz <das@FreeBSD.ORG>
5  * All rights reserved.
6  *
7  * Redistribution and use in source and binary forms, with or without
8  * modification, are permitted provided that the following conditions
9  * are met:
10  * 1. Redistributions of source code must retain the above copyright
11  *    notice, this list of conditions and the following disclaimer.
12  * 2. Redistributions in binary form must reproduce the above copyright
13  *    notice, this list of conditions and the following disclaimer in the
14  *    documentation and/or other materials provided with the distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26  * SUCH DAMAGE.
27  */
28 
29 #include <sys/cdefs.h>
30 __FBSDID("$FreeBSD$");
31 
32 #include <float.h>
33 #include <inttypes.h>
34 #include <limits.h>
35 #include <math.h>
36 #include <stdlib.h>
37 #include "../stdio/floatio.h"
38 #include "fpmath.h"
39 #include "gdtoaimp.h"
40 
41 /*
42  * ldtoa() is a wrapper for gdtoa() that makes it smell like dtoa(),
43  * except that the floating point argument is passed by reference.
44  * When dtoa() is passed a NaN or infinity, it sets expt to 9999.
45  * However, a long double could have a valid exponent of 9999, so we
46  * use INT_MAX in ldtoa() instead.
47  */
48 char *
49 __ldtoa(long double *ld, int mode, int ndigits, int *decpt, int *sign,
50     char **rve)
51 {
52 	FPI fpi = {
53 		LDBL_MANT_DIG,			/* nbits */
54 		LDBL_MIN_EXP - LDBL_MANT_DIG,	/* emin */
55 		LDBL_MAX_EXP - LDBL_MANT_DIG,	/* emax */
56 		FLT_ROUNDS,	       		/* rounding */
57 #ifdef Sudden_Underflow	/* unused, but correct anyway */
58 		1
59 #else
60 		0
61 #endif
62 	};
63 	int be, kind;
64 	char *ret;
65 	union IEEEl2bits u;
66 	uint32_t bits[(LDBL_MANT_DIG + 31) / 32];
67 	void *vbits = bits;
68 
69 	u.e = *ld;
70 
71 	/*
72 	 * gdtoa doesn't know anything about the sign of the number, so
73 	 * if the number is negative, we need to swap rounding modes of
74 	 * 2 (upwards) and 3 (downwards).
75 	 */
76 	*sign = u.bits.sign;
77 	fpi.rounding ^= (fpi.rounding >> 1) & u.bits.sign;
78 
79 	be = u.bits.exp - (LDBL_MAX_EXP - 1) - (LDBL_MANT_DIG - 1);
80 	LDBL_TO_ARRAY32(u, bits);
81 
82 	switch (fpclassify(u.e)) {
83 	case FP_NORMAL:
84 		kind = STRTOG_Normal;
85 #ifdef	LDBL_IMPLICIT_NBIT
86 		bits[LDBL_MANT_DIG / 32] |= 1 << ((LDBL_MANT_DIG - 1) % 32);
87 #endif /* LDBL_IMPLICIT_NBIT */
88 		break;
89 	case FP_ZERO:
90 		kind = STRTOG_Zero;
91 		break;
92 	case FP_SUBNORMAL:
93 		kind = STRTOG_Denormal;
94 		be++;
95 		break;
96 	case FP_INFINITE:
97 		kind = STRTOG_Infinite;
98 		break;
99 	case FP_NAN:
100 		kind = STRTOG_NaN;
101 		break;
102 	default:
103 		abort();
104 	}
105 
106 	ret = gdtoa(&fpi, be, vbits, &kind, mode, ndigits, decpt, rve);
107 	if (*decpt == -32768)
108 		*decpt = INT_MAX;
109 	return ret;
110 }
111