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1da177e4 LT |
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., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA | |
20 | */ | |
21 | /* | |
22 | * BEGIN_DESC | |
23 | * | |
24 | * File: | |
25 | * @(#) pa/spmath/dfsqrt.c $Revision: 1.1 $ | |
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 | |
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. | |
7022672e | 79 | * Fall through to negative test if negative infinity. |
1da177e4 LT |
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 | } |