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
30ieee754dp 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		/* FAAL THOROUGH */
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