1 /*
2 * Linux/PA-RISC Project (http://www.parisc-linux.org/)
3 *
4 * Floating-point emulation code
5 * Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org>
6 *
7 * This program is free software; you can redistribute it and/or modify
8 * it under the terms of the GNU General Public License as published by
9 * the Free Software Foundation; either version 2, or (at your option)
10 * any later version.
11 *
12 * This program is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
15 * GNU General Public License for more details.
16 *
17 * You should have received a copy of the GNU General Public License
18 * along with this program; if not, write to the Free Software
19 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
20 */
21 /*
22 * BEGIN_DESC
23 *
24 * File:
25 * @(#) pa/spmath/sfsqrt.c $Revision: $
26 *
27 * Purpose:
28 * Single Floating-point Square Root
29 *
30 * External Interfaces:
31 * sgl_fsqrt(srcptr,nullptr,dstptr,status)
32 *
33 * Internal Interfaces:
34 *
35 * Theory:
36 * <<please update with a overview of the operation of this file>>
37 *
38 * END_DESC
39 */
40
41
42 #include "float.h"
43 #include "sgl_float.h"
44
45 /*
46 * Single Floating-point Square Root
47 */
48
49 /*ARGSUSED*/
50 unsigned int
sgl_fsqrt(sgl_floating_point * srcptr,unsigned int * nullptr,sgl_floating_point * dstptr,unsigned int * status)51 sgl_fsqrt(
52 sgl_floating_point *srcptr,
53 unsigned int *nullptr,
54 sgl_floating_point *dstptr,
55 unsigned int *status)
56 {
57 register unsigned int src, result;
58 register int src_exponent;
59 register unsigned int newbit, sum;
60 register boolean guardbit = FALSE, even_exponent;
61
62 src = *srcptr;
63 /*
64 * check source operand for NaN or infinity
65 */
66 if ((src_exponent = Sgl_exponent(src)) == SGL_INFINITY_EXPONENT) {
67 /*
68 * is signaling NaN?
69 */
70 if (Sgl_isone_signaling(src)) {
71 /* trap if INVALIDTRAP enabled */
72 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
73 /* make NaN quiet */
74 Set_invalidflag();
75 Sgl_set_quiet(src);
76 }
77 /*
78 * Return quiet NaN or positive infinity.
79 * Fall thru to negative test if negative infinity.
80 */
81 if (Sgl_iszero_sign(src) || Sgl_isnotzero_mantissa(src)) {
82 *dstptr = src;
83 return(NOEXCEPTION);
84 }
85 }
86
87 /*
88 * check for zero source operand
89 */
90 if (Sgl_iszero_exponentmantissa(src)) {
91 *dstptr = src;
92 return(NOEXCEPTION);
93 }
94
95 /*
96 * check for negative source operand
97 */
98 if (Sgl_isone_sign(src)) {
99 /* trap if INVALIDTRAP enabled */
100 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
101 /* make NaN quiet */
102 Set_invalidflag();
103 Sgl_makequietnan(src);
104 *dstptr = src;
105 return(NOEXCEPTION);
106 }
107
108 /*
109 * Generate result
110 */
111 if (src_exponent > 0) {
112 even_exponent = Sgl_hidden(src);
113 Sgl_clear_signexponent_set_hidden(src);
114 }
115 else {
116 /* normalize operand */
117 Sgl_clear_signexponent(src);
118 src_exponent++;
119 Sgl_normalize(src,src_exponent);
120 even_exponent = src_exponent & 1;
121 }
122 if (even_exponent) {
123 /* exponent is even */
124 /* Add comment here. Explain why odd exponent needs correction */
125 Sgl_leftshiftby1(src);
126 }
127 /*
128 * Add comment here. Explain following algorithm.
129 *
130 * Trust me, it works.
131 *
132 */
133 Sgl_setzero(result);
134 newbit = 1 << SGL_P;
135 while (newbit && Sgl_isnotzero(src)) {
136 Sgl_addition(result,newbit,sum);
137 if(sum <= Sgl_all(src)) {
138 /* update result */
139 Sgl_addition(result,(newbit<<1),result);
140 Sgl_subtract(src,sum,src);
141 }
142 Sgl_rightshiftby1(newbit);
143 Sgl_leftshiftby1(src);
144 }
145 /* correct exponent for pre-shift */
146 if (even_exponent) {
147 Sgl_rightshiftby1(result);
148 }
149
150 /* check for inexact */
151 if (Sgl_isnotzero(src)) {
152 if (!even_exponent && Sgl_islessthan(result,src))
153 Sgl_increment(result);
154 guardbit = Sgl_lowmantissa(result);
155 Sgl_rightshiftby1(result);
156
157 /* now round result */
158 switch (Rounding_mode()) {
159 case ROUNDPLUS:
160 Sgl_increment(result);
161 break;
162 case ROUNDNEAREST:
163 /* stickybit is always true, so guardbit
164 * is enough to determine rounding */
165 if (guardbit) {
166 Sgl_increment(result);
167 }
168 break;
169 }
170 /* increment result exponent by 1 if mantissa overflowed */
171 if (Sgl_isone_hiddenoverflow(result)) src_exponent+=2;
172
173 if (Is_inexacttrap_enabled()) {
174 Sgl_set_exponent(result,
175 ((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
176 *dstptr = result;
177 return(INEXACTEXCEPTION);
178 }
179 else Set_inexactflag();
180 }
181 else {
182 Sgl_rightshiftby1(result);
183 }
184 Sgl_set_exponent(result,((src_exponent-SGL_BIAS)>>1)+SGL_BIAS);
185 *dstptr = result;
186 return(NOEXCEPTION);
187 }
188