1// SPDX-License-Identifier: GPL-2.0-only
2/* IEEE754 floating point arithmetic
3 * double precision: common utilities
4 */
5/*
6 * MIPS floating point support
7 * Copyright (C) 1994-2000 Algorithmics Ltd.
8 */
9
10#include "ieee754dp.h"
11
12union ieee754dp ieee754dp_add(union ieee754dp x, union ieee754dp y)
13{
14	int s;
15
16	COMPXDP;
17	COMPYDP;
18
19	EXPLODEXDP;
20	EXPLODEYDP;
21
22	ieee754_clearcx();
23
24	FLUSHXDP;
25	FLUSHYDP;
26
27	switch (CLPAIR(xc, yc)) {
28	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
29	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
30	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
31	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
32	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
33		return ieee754dp_nanxcpt(y);
34
35	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
36	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
37	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
38	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
39	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
40	case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
41		return ieee754dp_nanxcpt(x);
42
43	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
44	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
45	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
46	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
47		return y;
48
49	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
50	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
51	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
52	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
53	case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
54		return x;
55
56
57	/*
58	 * Infinity handling
59	 */
60	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
61		if (xs == ys)
62			return x;
63		ieee754_setcx(IEEE754_INVALID_OPERATION);
64		return ieee754dp_indef();
65
66	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
67	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
68	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
69		return y;
70
71	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
72	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
73	case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
74		return x;
75
76	/*
77	 * Zero handling
78	 */
79	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
80		if (xs == ys)
81			return x;
82		else
83			return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
84
85	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
86	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
87		return x;
88
89	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
90	case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
91		return y;
92
93	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
94		DPDNORMX;
95		fallthrough;
96	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
97		DPDNORMY;
98		break;
99
100	case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
101		DPDNORMX;
102		break;
103
104	case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
105		break;
106	}
107	assert(xm & DP_HIDDEN_BIT);
108	assert(ym & DP_HIDDEN_BIT);
109
110	/*
111	 * Provide guard,round and stick bit space.
112	 */
113	xm <<= 3;
114	ym <<= 3;
115
116	if (xe > ye) {
117		/*
118		 * Have to shift y fraction right to align.
119		 */
120		s = xe - ye;
121		ym = XDPSRS(ym, s);
122		ye += s;
123	} else if (ye > xe) {
124		/*
125		 * Have to shift x fraction right to align.
126		 */
127		s = ye - xe;
128		xm = XDPSRS(xm, s);
129		xe += s;
130	}
131	assert(xe == ye);
132	assert(xe <= DP_EMAX);
133
134	if (xs == ys) {
135		/*
136		 * Generate 28 bit result of adding two 27 bit numbers
137		 * leaving result in xm, xs and xe.
138		 */
139		xm = xm + ym;
140
141		if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */
142			xm = XDPSRS1(xm);
143			xe++;
144		}
145	} else {
146		if (xm >= ym) {
147			xm = xm - ym;
148		} else {
149			xm = ym - xm;
150			xs = ys;
151		}
152		if (xm == 0)
153			return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
154
155		/*
156		 * Normalize to rounding precision.
157		 */
158		while ((xm >> (DP_FBITS + 3)) == 0) {
159			xm <<= 1;
160			xe--;
161		}
162	}
163
164	return ieee754dp_format(xs, xe, xm);
165}
166