xref: /openbmc/linux/arch/mips/math-emu/dp_sub.c (revision b6dcefde)
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  * http://www.algor.co.uk
8  *
9  * ########################################################################
10  *
11  *  This program is free software; you can distribute it and/or modify it
12  *  under the terms of the GNU General Public License (Version 2) as
13  *  published by the Free Software Foundation.
14  *
15  *  This program is distributed in the hope it will be useful, but WITHOUT
16  *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17  *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
18  *  for more details.
19  *
20  *  You should have received a copy of the GNU General Public License along
21  *  with this program; if not, write to the Free Software Foundation, Inc.,
22  *  59 Temple Place - Suite 330, Boston MA 02111-1307, USA.
23  *
24  * ########################################################################
25  */
26 
27 
28 #include "ieee754dp.h"
29 
30 ieee754dp ieee754dp_sub(ieee754dp x, ieee754dp y)
31 {
32 	COMPXDP;
33 	COMPYDP;
34 
35 	EXPLODEXDP;
36 	EXPLODEYDP;
37 
38 	CLEARCX;
39 
40 	FLUSHXDP;
41 	FLUSHYDP;
42 
43 	switch (CLPAIR(xc, yc)) {
44 	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
45 	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
46 	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
47 	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
48 	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
49 	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
50 	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
51 	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
52 	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
53 	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
54 	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
55 		SETCX(IEEE754_INVALID_OPERATION);
56 		return ieee754dp_nanxcpt(ieee754dp_indef(), "sub", x, y);
57 
58 	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
59 	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
60 	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
61 	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
62 		return y;
63 
64 	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
65 	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
66 	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
67 	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
68 	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
69 		return x;
70 
71 
72 		/* Infinity handling
73 		 */
74 
75 	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
76 		if (xs != ys)
77 			return x;
78 		SETCX(IEEE754_INVALID_OPERATION);
79 		return ieee754dp_xcpt(ieee754dp_indef(), "sub", x, y);
80 
81 	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
82 	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
83 	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
84 		return ieee754dp_inf(ys ^ 1);
85 
86 	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
87 	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
88 	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
89 		return x;
90 
91 		/* Zero handling
92 		 */
93 
94 	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
95 		if (xs != ys)
96 			return x;
97 		else
98 			return ieee754dp_zero(ieee754_csr.rm ==
99 					      IEEE754_RD);
100 
101 	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
102 	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
103 		return x;
104 
105 	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
106 	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
107 		/* quick fix up */
108 		DPSIGN(y) ^= 1;
109 		return y;
110 
111 	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
112 		DPDNORMX;
113 		/* FALL THROUGH */
114 
115 	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
116 		/* normalize ym,ye */
117 		DPDNORMY;
118 		break;
119 
120 	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
121 		/* normalize xm,xe */
122 		DPDNORMX;
123 		break;
124 
125 	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
126 		break;
127 	}
128 	/* flip sign of y and handle as add */
129 	ys ^= 1;
130 
131 	assert(xm & DP_HIDDEN_BIT);
132 	assert(ym & DP_HIDDEN_BIT);
133 
134 
135 	/* provide guard,round and stick bit dpace */
136 	xm <<= 3;
137 	ym <<= 3;
138 
139 	if (xe > ye) {
140 		/* have to shift y fraction right to align
141 		 */
142 		int s = xe - ye;
143 		ym = XDPSRS(ym, s);
144 		ye += s;
145 	} else if (ye > xe) {
146 		/* have to shift x fraction right to align
147 		 */
148 		int s = ye - xe;
149 		xm = XDPSRS(xm, s);
150 		xe += s;
151 	}
152 	assert(xe == ye);
153 	assert(xe <= DP_EMAX);
154 
155 	if (xs == ys) {
156 		/* generate 28 bit result of adding two 27 bit numbers
157 		 */
158 		xm = xm + ym;
159 		xe = xe;
160 		xs = xs;
161 
162 		if (xm >> (DP_MBITS + 1 + 3)) {	/* carry out */
163 			xm = XDPSRS1(xm);	/* shift preserving sticky */
164 			xe++;
165 		}
166 	} else {
167 		if (xm >= ym) {
168 			xm = xm - ym;
169 			xe = xe;
170 			xs = xs;
171 		} else {
172 			xm = ym - xm;
173 			xe = xe;
174 			xs = ys;
175 		}
176 		if (xm == 0) {
177 			if (ieee754_csr.rm == IEEE754_RD)
178 				return ieee754dp_zero(1);	/* round negative inf. => sign = -1 */
179 			else
180 				return ieee754dp_zero(0);	/* other round modes   => sign = 1 */
181 		}
182 
183 		/* normalize to rounding precision
184 		 */
185 		while ((xm >> (DP_MBITS + 3)) == 0) {
186 			xm <<= 1;
187 			xe--;
188 		}
189 	}
190 	DPNORMRET2(xs, xe, xm, "sub", x, y);
191 }
192