1 /* $NetBSD: sfsqrt.c,v 1.6 2016/02/29 18:20:31 christos Exp $ */
2
3 /* $OpenBSD: sfsqrt.c,v 1.5 2001/03/29 03:58:19 mickey Exp $ */
4
5 /*
6 * Copyright 1996 1995 by Open Software Foundation, Inc.
7 * All Rights Reserved
8 *
9 * Permission to use, copy, modify, and distribute this software and
10 * its documentation for any purpose and without fee is hereby granted,
11 * provided that the above copyright notice appears in all copies and
12 * that both the copyright notice and this permission notice appear in
13 * supporting documentation.
14 *
15 * OSF DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE
16 * INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
17 * FOR A PARTICULAR PURPOSE.
18 *
19 * IN NO EVENT SHALL OSF BE LIABLE FOR ANY SPECIAL, INDIRECT, OR
20 * CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
21 * LOSS OF USE, DATA OR PROFITS, WHETHER IN ACTION OF CONTRACT,
22 * NEGLIGENCE, OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION
23 * WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
24 *
25 */
26 /*
27 * pmk1.1
28 */
29 /*
30 * (c) Copyright 1986 HEWLETT-PACKARD COMPANY
31 *
32 * To anyone who acknowledges that this file is provided "AS IS"
33 * without any express or implied warranty:
34 * permission to use, copy, modify, and distribute this file
35 * for any purpose is hereby granted without fee, provided that
36 * the above copyright notice and this notice appears in all
37 * copies, and that the name of Hewlett-Packard Company not be
38 * used in advertising or publicity pertaining to distribution
39 * of the software without specific, written prior permission.
40 * Hewlett-Packard Company makes no representations about the
41 * suitability of this software for any purpose.
42 */
43
44 #include <sys/cdefs.h>
45 __KERNEL_RCSID(0, "$NetBSD: sfsqrt.c,v 1.6 2016/02/29 18:20:31 christos Exp $");
46
47 #include "../spmath/float.h"
48 #include "../spmath/sgl_float.h"
49
50 /*
51 * Single Floating-point Square Root
52 */
53
54 /*ARGSUSED*/
55 int
sgl_fsqrt(sgl_floating_point * srcptr,sgl_floating_point * dstptr,unsigned int * status)56 sgl_fsqrt(sgl_floating_point *srcptr, sgl_floating_point *dstptr,
57 unsigned int *status)
58 {
59 register unsigned int src, result;
60 register int src_exponent, newbit, sum;
61 register int guardbit = false, even_exponent;
62
63 src = *srcptr;
64 /*
65 * check source operand for NaN or infinity
66 */
67 if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
68 /*
69 * is signaling NaN?
70 */
71 if (Sgl_isone_signaling(src)) {
72 /* trap if INVALIDTRAP enabled */
73 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
74 /* make NaN quiet */
75 Set_invalidflag();
76 Sgl_set_quiet(src);
77 }
78 /*
79 * Return quiet NaN or positive infinity.
80 * Fall thru to negative test if negative infinity.
81 */
82 if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
83 *dstptr = src;
84 return(NOEXCEPTION);
85 }
86 }
87
88 /*
89 * check for zero source operand
90 */
91 if (Sgl_iszero_exponentmantissa(src)) {
92 *dstptr = src;
93 return(NOEXCEPTION);
94 }
95
96 /*
97 * check for negative source operand
98 */
99 if (Sgl_isone_sign(src)) {
100 /* trap if INVALIDTRAP enabled */
101 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
102 /* make NaN quiet */
103 Set_invalidflag();
104 Sgl_makequietnan(src);
105 *dstptr = src;
106 return(NOEXCEPTION);
107 }
108
109 /*
110 * Generate result
111 */
112 if (src_exponent > 0) {
113 even_exponent = Sgl_hidden(src);
114 Sgl_clear_signexponent_set_hidden(src);
115 }
116 else {
117 /* normalize operand */
118 Sgl_clear_signexponent(src);
119 src_exponent++;
120 Sgl_normalize(src,src_exponent);
121 even_exponent = src_exponent & 1;
122 }
123 if (even_exponent) {
124 /* exponent is even */
125 /* Add comment here. Explain why odd exponent needs correction */
126 Sgl_leftshiftby1(src);
127 }
128 /*
129 * Add comment here. Explain following algorithm.
130 *
131 * Trust me, it works.
132 *
133 */
134 Sgl_setzero(result);
135 newbit = 1 << SGL_P;
136 while (newbit && Sgl_isnotzero(src)) {
137 Sgl_addition(result,newbit,sum);
138 if(sum <= Sgl_all(src)) {
139 /* update result */
140 Sgl_addition(result,(newbit<<1),result);
141 Sgl_subtract(src,sum,src);
142 }
143 Sgl_rightshiftby1(newbit);
144 Sgl_leftshiftby1(src);
145 }
146 /* correct exponent for pre-shift */
147 if (even_exponent) {
148 Sgl_rightshiftby1(result);
149 }
150
151 /* check for inexact */
152 if (Sgl_isnotzero(src)) {
153 if (!even_exponent && Sgl_islessthan(result,src))
154 Sgl_increment(result);
155 guardbit = Sgl_lowmantissa(result);
156 Sgl_rightshiftby1(result);
157
158 /* now round result */
159 switch (Rounding_mode()) {
160 case ROUNDPLUS:
161 Sgl_increment(result);
162 break;
163 case ROUNDNEAREST:
164 /* stickybit is always true, so guardbit
165 * is enough to determine rounding */
166 if (guardbit) {
167 Sgl_increment(result);
168 }
169 break;
170 }
171 /* increment result exponent by 1 if mantissa overflowed */
172 if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;
173
174 if (Is_inexacttrap_enabled()) {
175 Sgl_set_exponent(result,
176 ((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
177 *dstptr = result;
178 return(INEXACTEXCEPTION);
179 }
180 else Set_inexactflag();
181 }
182 else {
183 Sgl_rightshiftby1(result);
184 }
185 Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
186 *dstptr = result;
187 return(NOEXCEPTION);
188 }
189