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660662f8 | 1 | // SPDX-License-Identifier: GPL-2.0-or-later |
1da177e4 LT |
2 | /* |
3 | * Linux/PA-RISC Project (http://www.parisc-linux.org/) | |
4 | * | |
5 | * Floating-point emulation code | |
6 | * Copyright (C) 2001 Hewlett-Packard (Paul Bame) <bame@debian.org> | |
1da177e4 LT |
7 | */ |
8 | /* | |
9 | * BEGIN_DESC | |
10 | * | |
11 | * File: | |
12 | * @(#) pa/spmath/dfsqrt.c $Revision: 1.1 $ | |
13 | * | |
14 | * Purpose: | |
15 | * Double Floating-point Square Root | |
16 | * | |
17 | * External Interfaces: | |
18 | * dbl_fsqrt(srcptr,nullptr,dstptr,status) | |
19 | * | |
20 | * Internal Interfaces: | |
21 | * | |
22 | * Theory: | |
23 | * <<please update with a overview of the operation of this file>> | |
24 | * | |
25 | * END_DESC | |
26 | */ | |
27 | ||
28 | ||
29 | #include "float.h" | |
30 | #include "dbl_float.h" | |
31 | ||
32 | /* | |
33 | * Double Floating-point Square Root | |
34 | */ | |
35 | ||
36 | /*ARGSUSED*/ | |
37 | unsigned int | |
38 | dbl_fsqrt( | |
39 | dbl_floating_point *srcptr, | |
40 | unsigned int *nullptr, | |
41 | dbl_floating_point *dstptr, | |
42 | unsigned int *status) | |
43 | { | |
44 | register unsigned int srcp1, srcp2, resultp1, resultp2; | |
45 | register unsigned int newbitp1, newbitp2, sump1, sump2; | |
46 | register int src_exponent; | |
47 | register boolean guardbit = FALSE, even_exponent; | |
48 | ||
49 | Dbl_copyfromptr(srcptr,srcp1,srcp2); | |
50 | /* | |
51 | * check source operand for NaN or infinity | |
52 | */ | |
53 | if ((src_exponent = Dbl_exponent(srcp1)) == DBL_INFINITY_EXPONENT) { | |
54 | /* | |
55 | * is signaling NaN? | |
56 | */ | |
57 | if (Dbl_isone_signaling(srcp1)) { | |
58 | /* trap if INVALIDTRAP enabled */ | |
59 | if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); | |
60 | /* make NaN quiet */ | |
61 | Set_invalidflag(); | |
62 | Dbl_set_quiet(srcp1); | |
63 | } | |
64 | /* | |
65 | * Return quiet NaN or positive infinity. | |
7022672e | 66 | * Fall through to negative test if negative infinity. |
1da177e4 LT |
67 | */ |
68 | if (Dbl_iszero_sign(srcp1) || | |
69 | Dbl_isnotzero_mantissa(srcp1,srcp2)) { | |
70 | Dbl_copytoptr(srcp1,srcp2,dstptr); | |
71 | return(NOEXCEPTION); | |
72 | } | |
73 | } | |
74 | ||
75 | /* | |
76 | * check for zero source operand | |
77 | */ | |
78 | if (Dbl_iszero_exponentmantissa(srcp1,srcp2)) { | |
79 | Dbl_copytoptr(srcp1,srcp2,dstptr); | |
80 | return(NOEXCEPTION); | |
81 | } | |
82 | ||
83 | /* | |
84 | * check for negative source operand | |
85 | */ | |
86 | if (Dbl_isone_sign(srcp1)) { | |
87 | /* trap if INVALIDTRAP enabled */ | |
88 | if (Is_invalidtrap_enabled()) return(INVALIDEXCEPTION); | |
89 | /* make NaN quiet */ | |
90 | Set_invalidflag(); | |
91 | Dbl_makequietnan(srcp1,srcp2); | |
92 | Dbl_copytoptr(srcp1,srcp2,dstptr); | |
93 | return(NOEXCEPTION); | |
94 | } | |
95 | ||
96 | /* | |
97 | * Generate result | |
98 | */ | |
99 | if (src_exponent > 0) { | |
100 | even_exponent = Dbl_hidden(srcp1); | |
101 | Dbl_clear_signexponent_set_hidden(srcp1); | |
102 | } | |
103 | else { | |
104 | /* normalize operand */ | |
105 | Dbl_clear_signexponent(srcp1); | |
106 | src_exponent++; | |
107 | Dbl_normalize(srcp1,srcp2,src_exponent); | |
108 | even_exponent = src_exponent & 1; | |
109 | } | |
110 | if (even_exponent) { | |
111 | /* exponent is even */ | |
112 | /* Add comment here. Explain why odd exponent needs correction */ | |
113 | Dbl_leftshiftby1(srcp1,srcp2); | |
114 | } | |
115 | /* | |
116 | * Add comment here. Explain following algorithm. | |
117 | * | |
118 | * Trust me, it works. | |
119 | * | |
120 | */ | |
121 | Dbl_setzero(resultp1,resultp2); | |
122 | Dbl_allp1(newbitp1) = 1 << (DBL_P - 32); | |
123 | Dbl_setzero_mantissap2(newbitp2); | |
124 | while (Dbl_isnotzero(newbitp1,newbitp2) && Dbl_isnotzero(srcp1,srcp2)) { | |
125 | Dbl_addition(resultp1,resultp2,newbitp1,newbitp2,sump1,sump2); | |
126 | if(Dbl_isnotgreaterthan(sump1,sump2,srcp1,srcp2)) { | |
127 | Dbl_leftshiftby1(newbitp1,newbitp2); | |
128 | /* update result */ | |
129 | Dbl_addition(resultp1,resultp2,newbitp1,newbitp2, | |
130 | resultp1,resultp2); | |
131 | Dbl_subtract(srcp1,srcp2,sump1,sump2,srcp1,srcp2); | |
132 | Dbl_rightshiftby2(newbitp1,newbitp2); | |
133 | } | |
134 | else { | |
135 | Dbl_rightshiftby1(newbitp1,newbitp2); | |
136 | } | |
137 | Dbl_leftshiftby1(srcp1,srcp2); | |
138 | } | |
139 | /* correct exponent for pre-shift */ | |
140 | if (even_exponent) { | |
141 | Dbl_rightshiftby1(resultp1,resultp2); | |
142 | } | |
143 | ||
144 | /* check for inexact */ | |
145 | if (Dbl_isnotzero(srcp1,srcp2)) { | |
146 | if (!even_exponent && Dbl_islessthan(resultp1,resultp2,srcp1,srcp2)) { | |
147 | Dbl_increment(resultp1,resultp2); | |
148 | } | |
149 | guardbit = Dbl_lowmantissap2(resultp2); | |
150 | Dbl_rightshiftby1(resultp1,resultp2); | |
151 | ||
152 | /* now round result */ | |
153 | switch (Rounding_mode()) { | |
154 | case ROUNDPLUS: | |
155 | Dbl_increment(resultp1,resultp2); | |
156 | break; | |
157 | case ROUNDNEAREST: | |
158 | /* stickybit is always true, so guardbit | |
159 | * is enough to determine rounding */ | |
160 | if (guardbit) { | |
161 | Dbl_increment(resultp1,resultp2); | |
162 | } | |
163 | break; | |
164 | } | |
165 | /* increment result exponent by 1 if mantissa overflowed */ | |
166 | if (Dbl_isone_hiddenoverflow(resultp1)) src_exponent+=2; | |
167 | ||
168 | if (Is_inexacttrap_enabled()) { | |
169 | Dbl_set_exponent(resultp1, | |
170 | ((src_exponent-DBL_BIAS)>>1)+DBL_BIAS); | |
171 | Dbl_copytoptr(resultp1,resultp2,dstptr); | |
172 | return(INEXACTEXCEPTION); | |
173 | } | |
174 | else Set_inexactflag(); | |
175 | } | |
176 | else { | |
177 | Dbl_rightshiftby1(resultp1,resultp2); | |
178 | } | |
179 | Dbl_set_exponent(resultp1,((src_exponent-DBL_BIAS)>>1)+DBL_BIAS); | |
180 | Dbl_copytoptr(resultp1,resultp2,dstptr); | |
181 | return(NOEXCEPTION); | |
182 | } |