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sp_sub.c
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1 /* IEEE754 floating point arithmetic
2  * single precision
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 "ieee754sp.h"
28 
29 ieee754sp ieee754sp_sub(ieee754sp x, ieee754sp y)
30 {
31  COMPXSP;
32  COMPYSP;
33 
34  EXPLODEXSP;
35  EXPLODEYSP;
36 
37  CLEARCX;
38 
39  FLUSHXSP;
40  FLUSHYSP;
41 
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 ieee754sp_nanxcpt(ieee754sp_indef(), "sub", x, y);
56 
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):
61  return y;
62 
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):
68  return x;
69 
70 
71  /* Infinity handling
72  */
73 
74  case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
75  if (xs != ys)
76  return x;
77  SETCX(IEEE754_INVALID_OPERATION);
78  return ieee754sp_xcpt(ieee754sp_indef(), "sub", x, y);
79 
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 ieee754sp_inf(ys ^ 1);
84 
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):
88  return x;
89 
90  /* Zero handling
91  */
92 
93  case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
94  if (xs != ys)
95  return x;
96  else
97  return ieee754sp_zero(ieee754_csr.rm ==
98  IEEE754_RD);
99 
100  case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
101  case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
102  return x;
103 
104  case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
105  case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
106  /* quick fix up */
107  DPSIGN(y) ^= 1;
108  return y;
109 
110  case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
111  SPDNORMX;
112 
113  case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
114  SPDNORMY;
115  break;
116 
117  case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
118  SPDNORMX;
119  break;
120 
121  case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
122  break;
123  }
124  /* flip sign of y and handle as add */
125  ys ^= 1;
126 
127  assert(xm & SP_HIDDEN_BIT);
128  assert(ym & SP_HIDDEN_BIT);
129 
130 
131  /* provide guard,round and stick bit space */
132  xm <<= 3;
133  ym <<= 3;
134 
135  if (xe > ye) {
136  /* have to shift y fraction right to align
137  */
138  int s = xe - ye;
139  SPXSRSYn(s);
140  } else if (ye > xe) {
141  /* have to shift x fraction right to align
142  */
143  int s = ye - xe;
144  SPXSRSXn(s);
145  }
146  assert(xe == ye);
147  assert(xe <= SP_EMAX);
148 
149  if (xs == ys) {
150  /* generate 28 bit result of adding two 27 bit numbers
151  */
152  xm = xm + ym;
153  xe = xe;
154  xs = xs;
155 
156  if (xm >> (SP_MBITS + 1 + 3)) { /* carry out */
157  SPXSRSX1(); /* shift preserving sticky */
158  }
159  } else {
160  if (xm >= ym) {
161  xm = xm - ym;
162  xe = xe;
163  xs = xs;
164  } else {
165  xm = ym - xm;
166  xe = xe;
167  xs = ys;
168  }
169  if (xm == 0) {
170  if (ieee754_csr.rm == IEEE754_RD)
171  return ieee754sp_zero(1); /* round negative inf. => sign = -1 */
172  else
173  return ieee754sp_zero(0); /* other round modes => sign = 1 */
174  }
175  /* normalize to rounding precision
176  */
177  while ((xm >> (SP_MBITS + 3)) == 0) {
178  xm <<= 1;
179  xe--;
180  }
181  }
182  SPNORMRET2(xs, xe, xm, "sub", x, y);
183 }
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