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/dfsqrt.c $Revision: $
26 *
27 * Purpose:
28 * Double Floating-point Square Root
29 *
30 * External Interfaces:
31 * dbl_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 "dbl_float.h"
44
45 /*
46 * Double Floating-point Square Root
47 */
48
49 /*ARGSUSED*/
50 unsigned int
dbl_fsqrt(dbl_floating_point * srcptr,unsigned int * nullptr,dbl_floating_point * dstptr,unsigned int * status)51 dbl_fsqrt(
52 dbl_floating_point *srcptr,
53 unsigned int *nullptr,
54 dbl_floating_point *dstptr,
55 unsigned int *status)
56 {
57 register unsigned int srcp1, srcp2, resultp1, resultp2;
58 register unsigned int newbitp1, newbitp2, sump1, sump2;
59 register int src_exponent;
60 register boolean guardbit = FALSE, even_exponent;
61
62 Dbl_copyfromptr(srcptr,srcp1,srcp2);
63 /*
64 * check source operand for NaN or infinity
65 */
66 if ((src_exponent = Dbl_exponent(srcp1)) == DBL_INFINITY_EXPONENT) {
67 /*
68 * is signaling NaN?
69 */
70 if (Dbl_isone_signaling(srcp1)) {
71 /* trap if INVALIDTRAP enabled */
72 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
73 /* make NaN quiet */
74 Set_invalidflag();
75 Dbl_set_quiet(srcp1);
76 }
77 /*
78 * Return quiet NaN or positive infinity.
79 * Fall thru to negative test if negative infinity.
80 */
81 if (Dbl_iszero_sign(srcp1) ||
82 Dbl_isnotzero_mantissa(srcp1,srcp2)) {
83 Dbl_copytoptr(srcp1,srcp2,dstptr);
84 return(NOEXCEPTION);
85 }
86 }
87
88 /*
89 * check for zero source operand
90 */
91 if (Dbl_iszero_exponentmantissa(srcp1,srcp2)) {
92 Dbl_copytoptr(srcp1,srcp2,dstptr);
93 return(NOEXCEPTION);
94 }
95
96 /*
97 * check for negative source operand
98 */
99 if (Dbl_isone_sign(srcp1)) {
100 /* trap if INVALIDTRAP enabled */
101 if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION);
102 /* make NaN quiet */
103 Set_invalidflag();
104 Dbl_makequietnan(srcp1,srcp2);
105 Dbl_copytoptr(srcp1,srcp2,dstptr);
106 return(NOEXCEPTION);
107 }
108
109 /*
110 * Generate result
111 */
112 if (src_exponent > 0) {
113 even_exponent = Dbl_hidden(srcp1);
114 Dbl_clear_signexponent_set_hidden(srcp1);
115 }
116 else {
117 /* normalize operand */
118 Dbl_clear_signexponent(srcp1);
119 src_exponent++;
120 Dbl_normalize(srcp1,srcp2,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 Dbl_leftshiftby1(srcp1,srcp2);
127 }
128 /*
129 * Add comment here. Explain following algorithm.
130 *
131 * Trust me, it works.
132 *
133 */
134 Dbl_setzero(resultp1,resultp2);
135 Dbl_allp1(newbitp1) = 1 << (DBL_P - 32);
136 Dbl_setzero_mantissap2(newbitp2);
137 while (Dbl_isnotzero(newbitp1,newbitp2) && Dbl_isnotzero(srcp1,srcp2)) {
138 Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,sump1,sump2);
139 if(Dbl_isnotgreaterthan(sump1,sump2,srcp1,srcp2)) {
140 Dbl_leftshiftby1(newbitp1,newbitp2);
141 /* update result */
142 Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,
143 resultp1,resultp2);
144 Dbl_subtract(srcp1,srcp2,sump1,sump2,srcp1,srcp2);
145 Dbl_rightshiftby2(newbitp1,newbitp2);
146 }
147 else {
148 Dbl_rightshiftby1(newbitp1,newbitp2);
149 }
150 Dbl_leftshiftby1(srcp1,srcp2);
151 }
152 /* correct exponent for pre-shift */
153 if (even_exponent) {
154 Dbl_rightshiftby1(resultp1,resultp2);
155 }
156
157 /* check for inexact */
158 if (Dbl_isnotzero(srcp1,srcp2)) {
159 if (!even_exponent && Dbl_islessthan(resultp1,resultp2,srcp1,srcp2)) {
160 Dbl_increment(resultp1,resultp2);
161 }
162 guardbit = Dbl_lowmantissap2(resultp2);
163 Dbl_rightshiftby1(resultp1,resultp2);
164
165 /* now round result */
166 switch (Rounding_mode()) {
167 case ROUNDPLUS:
168 Dbl_increment(resultp1,resultp2);
169 break;
170 case ROUNDNEAREST:
171 /* stickybit is always true, so guardbit
172 * is enough to determine rounding */
173 if (guardbit) {
174 Dbl_increment(resultp1,resultp2);
175 }
176 break;
177 }
178 /* increment result exponent by 1 if mantissa overflowed */
179 if (Dbl_isone_hiddenoverflow(resultp1)) src_exponent+=2;
180
181 if (Is_inexacttrap_enabled()) {
182 Dbl_set_exponent(resultp1,
183 ((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
184 Dbl_copytoptr(resultp1,resultp2,dstptr);
185 return(INEXACTEXCEPTION);
186 }
187 else Set_inexactflag();
188 }
189 else {
190 Dbl_rightshiftby1(resultp1,resultp2);
191 }
192 Dbl_set_exponent(resultp1,((src_exponent-DBL_BIAS)>>1)+DBL_BIAS);
193 Dbl_copytoptr(resultp1,resultp2,dstptr);
194 return(NOEXCEPTION);
195 }
196