1*4882a593Smuzhiyun // SPDX-License-Identifier: GPL-2.0-only
2*4882a593Smuzhiyun /* IEEE754 floating point arithmetic
3*4882a593Smuzhiyun * double precision: common utilities
4*4882a593Smuzhiyun */
5*4882a593Smuzhiyun /*
6*4882a593Smuzhiyun * MIPS floating point support
7*4882a593Smuzhiyun * Copyright (C) 1994-2000 Algorithmics Ltd.
8*4882a593Smuzhiyun */
9*4882a593Smuzhiyun
10*4882a593Smuzhiyun #include "ieee754dp.h"
11*4882a593Smuzhiyun
ieee754dp_sub(union ieee754dp x,union ieee754dp y)12*4882a593Smuzhiyun union ieee754dp ieee754dp_sub(union ieee754dp x, union ieee754dp y)
13*4882a593Smuzhiyun {
14*4882a593Smuzhiyun int s;
15*4882a593Smuzhiyun
16*4882a593Smuzhiyun COMPXDP;
17*4882a593Smuzhiyun COMPYDP;
18*4882a593Smuzhiyun
19*4882a593Smuzhiyun EXPLODEXDP;
20*4882a593Smuzhiyun EXPLODEYDP;
21*4882a593Smuzhiyun
22*4882a593Smuzhiyun ieee754_clearcx();
23*4882a593Smuzhiyun
24*4882a593Smuzhiyun FLUSHXDP;
25*4882a593Smuzhiyun FLUSHYDP;
26*4882a593Smuzhiyun
27*4882a593Smuzhiyun switch (CLPAIR(xc, yc)) {
28*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_SNAN):
29*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_SNAN):
30*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_SNAN):
31*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_SNAN):
32*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_SNAN):
33*4882a593Smuzhiyun return ieee754dp_nanxcpt(y);
34*4882a593Smuzhiyun
35*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_SNAN):
36*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_QNAN):
37*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_ZERO):
38*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_NORM):
39*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_DNORM):
40*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_SNAN, IEEE754_CLASS_INF):
41*4882a593Smuzhiyun return ieee754dp_nanxcpt(x);
42*4882a593Smuzhiyun
43*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_QNAN):
44*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_QNAN):
45*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_QNAN):
46*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_QNAN):
47*4882a593Smuzhiyun return y;
48*4882a593Smuzhiyun
49*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_QNAN):
50*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_ZERO):
51*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_NORM):
52*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_DNORM):
53*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_QNAN, IEEE754_CLASS_INF):
54*4882a593Smuzhiyun return x;
55*4882a593Smuzhiyun
56*4882a593Smuzhiyun
57*4882a593Smuzhiyun /*
58*4882a593Smuzhiyun * Infinity handling
59*4882a593Smuzhiyun */
60*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_INF):
61*4882a593Smuzhiyun if (xs != ys)
62*4882a593Smuzhiyun return x;
63*4882a593Smuzhiyun ieee754_setcx(IEEE754_INVALID_OPERATION);
64*4882a593Smuzhiyun return ieee754dp_indef();
65*4882a593Smuzhiyun
66*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_INF):
67*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_INF):
68*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_INF):
69*4882a593Smuzhiyun return ieee754dp_inf(ys ^ 1);
70*4882a593Smuzhiyun
71*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_ZERO):
72*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_NORM):
73*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_INF, IEEE754_CLASS_DNORM):
74*4882a593Smuzhiyun return x;
75*4882a593Smuzhiyun
76*4882a593Smuzhiyun /*
77*4882a593Smuzhiyun * Zero handling
78*4882a593Smuzhiyun */
79*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_ZERO):
80*4882a593Smuzhiyun if (xs != ys)
81*4882a593Smuzhiyun return x;
82*4882a593Smuzhiyun else
83*4882a593Smuzhiyun return ieee754dp_zero(ieee754_csr.rm == FPU_CSR_RD);
84*4882a593Smuzhiyun
85*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_ZERO):
86*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_ZERO):
87*4882a593Smuzhiyun return x;
88*4882a593Smuzhiyun
89*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_NORM):
90*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_ZERO, IEEE754_CLASS_DNORM):
91*4882a593Smuzhiyun /* quick fix up */
92*4882a593Smuzhiyun DPSIGN(y) ^= 1;
93*4882a593Smuzhiyun return y;
94*4882a593Smuzhiyun
95*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_DNORM):
96*4882a593Smuzhiyun DPDNORMX;
97*4882a593Smuzhiyun fallthrough;
98*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_DNORM):
99*4882a593Smuzhiyun /* normalize ym,ye */
100*4882a593Smuzhiyun DPDNORMY;
101*4882a593Smuzhiyun break;
102*4882a593Smuzhiyun
103*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_DNORM, IEEE754_CLASS_NORM):
104*4882a593Smuzhiyun /* normalize xm,xe */
105*4882a593Smuzhiyun DPDNORMX;
106*4882a593Smuzhiyun break;
107*4882a593Smuzhiyun
108*4882a593Smuzhiyun case CLPAIR(IEEE754_CLASS_NORM, IEEE754_CLASS_NORM):
109*4882a593Smuzhiyun break;
110*4882a593Smuzhiyun }
111*4882a593Smuzhiyun /* flip sign of y and handle as add */
112*4882a593Smuzhiyun ys ^= 1;
113*4882a593Smuzhiyun
114*4882a593Smuzhiyun assert(xm & DP_HIDDEN_BIT);
115*4882a593Smuzhiyun assert(ym & DP_HIDDEN_BIT);
116*4882a593Smuzhiyun
117*4882a593Smuzhiyun
118*4882a593Smuzhiyun /* provide guard,round and stick bit dpace */
119*4882a593Smuzhiyun xm <<= 3;
120*4882a593Smuzhiyun ym <<= 3;
121*4882a593Smuzhiyun
122*4882a593Smuzhiyun if (xe > ye) {
123*4882a593Smuzhiyun /*
124*4882a593Smuzhiyun * Have to shift y fraction right to align
125*4882a593Smuzhiyun */
126*4882a593Smuzhiyun s = xe - ye;
127*4882a593Smuzhiyun ym = XDPSRS(ym, s);
128*4882a593Smuzhiyun ye += s;
129*4882a593Smuzhiyun } else if (ye > xe) {
130*4882a593Smuzhiyun /*
131*4882a593Smuzhiyun * Have to shift x fraction right to align
132*4882a593Smuzhiyun */
133*4882a593Smuzhiyun s = ye - xe;
134*4882a593Smuzhiyun xm = XDPSRS(xm, s);
135*4882a593Smuzhiyun xe += s;
136*4882a593Smuzhiyun }
137*4882a593Smuzhiyun assert(xe == ye);
138*4882a593Smuzhiyun assert(xe <= DP_EMAX);
139*4882a593Smuzhiyun
140*4882a593Smuzhiyun if (xs == ys) {
141*4882a593Smuzhiyun /* generate 28 bit result of adding two 27 bit numbers
142*4882a593Smuzhiyun */
143*4882a593Smuzhiyun xm = xm + ym;
144*4882a593Smuzhiyun
145*4882a593Smuzhiyun if (xm >> (DP_FBITS + 1 + 3)) { /* carry out */
146*4882a593Smuzhiyun xm = XDPSRS1(xm); /* shift preserving sticky */
147*4882a593Smuzhiyun xe++;
148*4882a593Smuzhiyun }
149*4882a593Smuzhiyun } else {
150*4882a593Smuzhiyun if (xm >= ym) {
151*4882a593Smuzhiyun xm = xm - ym;
152*4882a593Smuzhiyun } else {
153*4882a593Smuzhiyun xm = ym - xm;
154*4882a593Smuzhiyun xs = ys;
155*4882a593Smuzhiyun }
156*4882a593Smuzhiyun if (xm == 0) {
157*4882a593Smuzhiyun if (ieee754_csr.rm == FPU_CSR_RD)
158*4882a593Smuzhiyun return ieee754dp_zero(1); /* round negative inf. => sign = -1 */
159*4882a593Smuzhiyun else
160*4882a593Smuzhiyun return ieee754dp_zero(0); /* other round modes => sign = 1 */
161*4882a593Smuzhiyun }
162*4882a593Smuzhiyun
163*4882a593Smuzhiyun /* normalize to rounding precision
164*4882a593Smuzhiyun */
165*4882a593Smuzhiyun while ((xm >> (DP_FBITS + 3)) == 0) {
166*4882a593Smuzhiyun xm <<= 1;
167*4882a593Smuzhiyun xe--;
168*4882a593Smuzhiyun }
169*4882a593Smuzhiyun }
170*4882a593Smuzhiyun
171*4882a593Smuzhiyun return ieee754dp_format(xs, xe, xm);
172*4882a593Smuzhiyun }
173