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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/sfsqrt.c $Revision: 1.1 $ | |
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 | |
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. | |
7022672e | 79 | * Fall through to negative test if negative infinity. |
1da177e4 LT |
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 | } |