xref: /titanic_51/usr/src/lib/libm/common/m9x/nearbyintf.c (revision 0ed5c46e82c989cfa9726d9dae452e3d24ef83be)
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 2011 Nexenta Systems, Inc.  All rights reserved.
24  */
25 /*
26  * Copyright 2006 Sun Microsystems, Inc.  All rights reserved.
27  * Use is subject to license terms.
28  */
29 
30 #if defined(ELFOBJ)
31 #pragma weak nearbyintf = __nearbyintf
32 #endif
33 
34 #include "libm.h"
35 #include "fenv_synonyms.h"
36 #include <fenv.h>
37 
38 float
39 __nearbyintf(float x) {
40 	union {
41 		unsigned i;
42 		float f;
43 	} xx;
44 	unsigned hx, sx, i, frac;
45 	int rm;
46 
47 	xx.f = x;
48 	sx = xx.i & 0x80000000;
49 	hx = xx.i & ~0x80000000;
50 
51 	/* handle trivial cases */
52 	if (hx >= 0x4b000000) {	/* x is nan, inf, or already integral */
53 		if (hx > 0x7f800000)	/* x is nan */
54 			return (x * x);		/* + -> * for Cheetah */
55 		return (x);
56 	} else if (hx == 0)		/* x is zero */
57 		return (x);
58 
59 	/* get the rounding mode */
60 	rm = fegetround();
61 
62 	/* flip the sense of directed roundings if x is negative */
63 	if (sx && (rm == FE_UPWARD || rm == FE_DOWNWARD))
64 		rm = (FE_UPWARD + FE_DOWNWARD) - rm;
65 
66 	/* handle |x| < 1 */
67 	if (hx < 0x3f800000) {
68 		if (rm == FE_UPWARD || (rm == FE_TONEAREST && hx > 0x3f000000))
69 			xx.i = sx | 0x3f800000;
70 		else
71 			xx.i = sx;
72 		return (xx.f);
73 	}
74 
75 	/* round x at the integer bit */
76 	i = 1 << (0x96 - (hx >> 23));
77 	frac = hx & (i - 1);
78 	if (!frac)
79 		return (x);
80 
81 	hx &= ~(i - 1);
82 	if (rm == FE_UPWARD || (rm == FE_TONEAREST && (frac > (i >> 1) ||
83 		((frac == (i >> 1)) && (hx & i)))))
84 		xx.i = sx | (hx + i);
85 	else
86 		xx.i = sx | hx;
87 	return (xx.f);
88 }
89 
90 #if 0
91 
92 /*
93  * Alternate implementations for SPARC, x86, using fp ops.  These may
94  * be faster depending on how expensive saving and restoring the fp
95  * modes and status flags is.
96  */
97 
98 #include "libm.h"
99 #include "fma.h"
100 
101 #if defined(__sparc)
102 
103 float
104 __nearbyintf(float x) {
105 	union {
106 		unsigned i;
107 		float f;
108 	} xx, yy;
109 	float z;
110 	unsigned hx, sx, fsr, oldfsr;
111 	int rm;
112 
113 	xx.f = x;
114 	sx = xx.i & 0x80000000;
115 	hx = xx.i & ~0x80000000;
116 
117 	/* handle trivial cases */
118 	if (hx >= 0x4b000000)	/* x is nan, inf, or already integral */
119 		return (x + 0.0f);
120 	else if (hx == 0)	/* x is zero */
121 		return (x);
122 
123 	/* save the fsr */
124 	__fenv_getfsr(&oldfsr);
125 
126 	/* handle |x| < 1 */
127 	if (hx < 0x3f800000) {
128 		/* flip the sense of directed roundings if x is negative */
129 		rm = oldfsr >> 30;
130 		if (sx)
131 			rm ^= rm >> 1;
132 		if (rm == FSR_RP || (rm == FSR_RN && hx > 0x3f000000))
133 			xx.i = sx | 0x3f800000;
134 		else
135 			xx.i = sx;
136 		return (xx.f);
137 	}
138 
139 	/* clear the inexact trap */
140 	fsr = oldfsr & ~FSR_NXM;
141 	__fenv_setfsr(&fsr);
142 
143 	/* round x at the integer bit */
144 	yy.i = sx | 0x4b000000;
145 	z = (x + yy.f) - yy.f;
146 
147 	/* restore the old fsr */
148 	__fenv_setfsr(&oldfsr);
149 
150 	return (z);
151 }
152 
153 #elif defined(__x86)
154 
155 /* inline template */
156 extern long double frndint(long double);
157 
158 float
159 __nearbyintf(float x) {
160 	long double z;
161 	unsigned oldcwsw, cwsw;
162 
163 	/* save the control and status words, mask the inexact exception */
164 	__fenv_getcwsw(&oldcwsw);
165 	cwsw = oldcwsw | 0x00200000;
166 	__fenv_setcwsw(&cwsw);
167 
168 	z = frndint((long double) x);
169 
170 	/*
171 	 * restore the control and status words, preserving all but the
172 	 * inexact flag
173 	 */
174 	__fenv_getcwsw(&cwsw);
175 	oldcwsw |= (cwsw & 0x1f);
176 	__fenv_setcwsw(&oldcwsw);
177 
178 	/* note: the value of z is representable in single precision */
179 	return (z);
180 }
181 
182 #else
183 #error Unknown architecture
184 #endif
185 
186 #endif
187