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Linux/arch/mips/math-emu/ieee754dp.c

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  1 /* IEEE754 floating point arithmetic
  2  * double precision: common utilities
  3  */
  4 /*
  5  * MIPS floating point support
  6  * Copyright (C) 1994-2000 Algorithmics Ltd.
  7  *
  8  * ########################################################################
  9  *
 10  *  This program is free software; you can distribute it and/or modify it
 11  *  under the terms of the GNU General Public License (Version 2) as
 12  *  published by the Free Software Foundation.
 13  *
 14  *  This program is distributed in the hope it will be useful, but WITHOUT
 15  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 16  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 17  *  for more details.
 18  *
 19  *  You should have received a copy of the GNU General Public License along
 20  *  with this program; if not, write to the Free Software Foundation, Inc.,
 21  *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
 22  *
 23  * ########################################################################
 24  */
 25 
 26 
 27 #include "ieee754dp.h"
 28 
 29 int ieee754dp_class(ieee754dp x)
 30 {
 31         COMPXDP;
 32         EXPLODEXDP;
 33         return xc;
 34 }
 35 
 36 int ieee754dp_isnan(ieee754dp x)
 37 {
 38         return ieee754dp_class(x) >= IEEE754_CLASS_SNAN;
 39 }
 40 
 41 int ieee754dp_issnan(ieee754dp x)
 42 {
 43         assert(ieee754dp_isnan(x));
 44         return ((DPMANT(x) & DP_MBIT(DP_MBITS-1)) == DP_MBIT(DP_MBITS-1));
 45 }
 46 
 47 
 48 ieee754dp ieee754dp_xcpt(ieee754dp r, const char *op, ...)
 49 {
 50         struct ieee754xctx ax;
 51         if (!TSTX())
 52                 return r;
 53 
 54         ax.op = op;
 55         ax.rt = IEEE754_RT_DP;
 56         ax.rv.dp = r;
 57         va_start(ax.ap, op);
 58         ieee754_xcpt(&ax);
 59         va_end(ax.ap);
 60         return ax.rv.dp;
 61 }
 62 
 63 ieee754dp ieee754dp_nanxcpt(ieee754dp r, const char *op, ...)
 64 {
 65         struct ieee754xctx ax;
 66 
 67         assert(ieee754dp_isnan(r));
 68 
 69         if (!ieee754dp_issnan(r))       /* QNAN does not cause invalid op !! */
 70                 return r;
 71 
 72         if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
 73                 /* not enabled convert to a quiet NaN */
 74                 DPMANT(r) &= (~DP_MBIT(DP_MBITS-1));
 75                 if (ieee754dp_isnan(r))
 76                         return r;
 77                 else
 78                         return ieee754dp_indef();
 79         }
 80 
 81         ax.op = op;
 82         ax.rt = 0;
 83         ax.rv.dp = r;
 84         va_start(ax.ap, op);
 85         ieee754_xcpt(&ax);
 86         va_end(ax.ap);
 87         return ax.rv.dp;
 88 }
 89 
 90 ieee754dp ieee754dp_bestnan(ieee754dp x, ieee754dp y)
 91 {
 92         assert(ieee754dp_isnan(x));
 93         assert(ieee754dp_isnan(y));
 94 
 95         if (DPMANT(x) > DPMANT(y))
 96                 return x;
 97         else
 98                 return y;
 99 }
100 
101 
102 static u64 get_rounding(int sn, u64 xm)
103 {
104         /* inexact must round of 3 bits
105          */
106         if (xm & (DP_MBIT(3) - 1)) {
107                 switch (ieee754_csr.rm) {
108                 case IEEE754_RZ:
109                         break;
110                 case IEEE754_RN:
111                         xm += 0x3 + ((xm >> 3) & 1);
112                         /* xm += (xm&0x8)?0x4:0x3 */
113                         break;
114                 case IEEE754_RU:        /* toward +Infinity */
115                         if (!sn)        /* ?? */
116                                 xm += 0x8;
117                         break;
118                 case IEEE754_RD:        /* toward -Infinity */
119                         if (sn) /* ?? */
120                                 xm += 0x8;
121                         break;
122                 }
123         }
124         return xm;
125 }
126 
127 
128 /* generate a normal/denormal number with over,under handling
129  * sn is sign
130  * xe is an unbiased exponent
131  * xm is 3bit extended precision value.
132  */
133 ieee754dp ieee754dp_format(int sn, int xe, u64 xm)
134 {
135         assert(xm);             /* we don't gen exact zeros (probably should) */
136 
137         assert((xm >> (DP_MBITS + 1 + 3)) == 0);        /* no execess */
138         assert(xm & (DP_HIDDEN_BIT << 3));
139 
140         if (xe < DP_EMIN) {
141                 /* strip lower bits */
142                 int es = DP_EMIN - xe;
143 
144                 if (ieee754_csr.nod) {
145                         SETCX(IEEE754_UNDERFLOW);
146                         SETCX(IEEE754_INEXACT);
147 
148                         switch(ieee754_csr.rm) {
149                         case IEEE754_RN:
150                         case IEEE754_RZ:
151                                 return ieee754dp_zero(sn);
152                         case IEEE754_RU:    /* toward +Infinity */
153                                 if(sn == 0)
154                                         return ieee754dp_min(0);
155                                 else
156                                         return ieee754dp_zero(1);
157                         case IEEE754_RD:    /* toward -Infinity */
158                                 if(sn == 0)
159                                         return ieee754dp_zero(0);
160                                 else
161                                         return ieee754dp_min(1);
162                         }
163                 }
164 
165                 if (xe == DP_EMIN - 1
166                                 && get_rounding(sn, xm) >> (DP_MBITS + 1 + 3))
167                 {
168                         /* Not tiny after rounding */
169                         SETCX(IEEE754_INEXACT);
170                         xm = get_rounding(sn, xm);
171                         xm >>= 1;
172                         /* Clear grs bits */
173                         xm &= ~(DP_MBIT(3) - 1);
174                         xe++;
175                 }
176                 else {
177                         /* sticky right shift es bits
178                          */
179                         xm = XDPSRS(xm, es);
180                         xe += es;
181                         assert((xm & (DP_HIDDEN_BIT << 3)) == 0);
182                         assert(xe == DP_EMIN);
183                 }
184         }
185         if (xm & (DP_MBIT(3) - 1)) {
186                 SETCX(IEEE754_INEXACT);
187                 if ((xm & (DP_HIDDEN_BIT << 3)) == 0) {
188                         SETCX(IEEE754_UNDERFLOW);
189                 }
190 
191                 /* inexact must round of 3 bits
192                  */
193                 xm = get_rounding(sn, xm);
194                 /* adjust exponent for rounding add overflowing
195                  */
196                 if (xm >> (DP_MBITS + 3 + 1)) {
197                         /* add causes mantissa overflow */
198                         xm >>= 1;
199                         xe++;
200                 }
201         }
202         /* strip grs bits */
203         xm >>= 3;
204 
205         assert((xm >> (DP_MBITS + 1)) == 0);    /* no execess */
206         assert(xe >= DP_EMIN);
207 
208         if (xe > DP_EMAX) {
209                 SETCX(IEEE754_OVERFLOW);
210                 SETCX(IEEE754_INEXACT);
211                 /* -O can be table indexed by (rm,sn) */
212                 switch (ieee754_csr.rm) {
213                 case IEEE754_RN:
214                         return ieee754dp_inf(sn);
215                 case IEEE754_RZ:
216                         return ieee754dp_max(sn);
217                 case IEEE754_RU:        /* toward +Infinity */
218                         if (sn == 0)
219                                 return ieee754dp_inf(0);
220                         else
221                                 return ieee754dp_max(1);
222                 case IEEE754_RD:        /* toward -Infinity */
223                         if (sn == 0)
224                                 return ieee754dp_max(0);
225                         else
226                                 return ieee754dp_inf(1);
227                 }
228         }
229         /* gen norm/denorm/zero */
230 
231         if ((xm & DP_HIDDEN_BIT) == 0) {
232                 /* we underflow (tiny/zero) */
233                 assert(xe == DP_EMIN);
234                 if (ieee754_csr.mx & IEEE754_UNDERFLOW)
235                         SETCX(IEEE754_UNDERFLOW);
236                 return builddp(sn, DP_EMIN - 1 + DP_EBIAS, xm);
237         } else {
238                 assert((xm >> (DP_MBITS + 1)) == 0);    /* no execess */
239                 assert(xm & DP_HIDDEN_BIT);
240 
241                 return builddp(sn, xe + DP_EBIAS, xm & ~DP_HIDDEN_BIT);
242         }
243 }
244 

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