Pull misc into release branch
[linux-2.6] / arch / parisc / math-emu / dfsqrt.c
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.
79                  *  Fall through 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 }