1 /* IEEE754 floating point arithmetic
2 * double precision: common utilities
5 * MIPS floating point support
6 * Copyright (C) 1994-2000 Algorithmics Ltd.
8 * ########################################################################
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.
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
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.
23 * ########################################################################
27 #include "ieee754dp.h"
29 ieee754dp ieee754dp_sub(ieee754dp x, ieee754dp y)
42 switch (CLPAIR(xc, yc)) {
43 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
44 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
45 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
46 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
47 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
48 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
49 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
50 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
51 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
52 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
53 case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
54 SETCX(IEEE754_INVALID_OPERATION);
55 return ieee754dp_nanxcpt(ieee754dp_indef(), "sub", x, y);
57 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
58 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
59 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
60 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
63 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
64 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
65 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
66 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
67 case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
74 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
77 SETCX(IEEE754_INVALID_OPERATION);
78 return ieee754dp_xcpt(ieee754dp_indef(), "sub", x, y);
80 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
81 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
82 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
83 return ieee754dp_inf(ys ^ 1);
85 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
86 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
87 case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
93 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
97 return ieee754dp_zero(ieee754_csr.rm ==
100 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
101 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
104 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
105 case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
110 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
114 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
115 /* normalize ym,ye */
119 case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
120 /* normalize xm,xe */
124 case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
127 /* flip sign of y and handle as add */
130 assert(xm & DP_HIDDEN_BIT);
131 assert(ym & DP_HIDDEN_BIT);
134 /* provide guard,round and stick bit dpace */
139 /* have to shift y fraction right to align
144 } else if (ye > xe) {
145 /* have to shift x fraction right to align
152 assert(xe <= DP_EMAX);
155 /* generate 28 bit result of adding two 27 bit numbers
161 if (xm >> (DP_MBITS + 1 + 3)) { /* carry out */
162 xm = XDPSRS1(xm); /* shift preserving sticky */
176 if (ieee754_csr.rm == IEEE754_RD)
177 return ieee754dp_zero(1); /* round negative inf. => sign = -1 */
179 return ieee754dp_zero(0); /* other round modes => sign = 1 */
182 /* normalize to rounding precision
184 while ((xm >> (DP_MBITS + 3)) == 0) {
189 DPNORMRET2(xs, xe, xm, "sub", x, y);