xref: /linux/arch/mips/math-emu/ieee754sp.c (revision d39d0ed196aa1685bb24771e92f78633c66ac9cb)
1 /* IEEE754 floating point arithmetic
2  * single precision
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 "ieee754sp.h"
29 
30 int ieee754sp_class(ieee754sp x)
31 {
32 	COMPXSP;
33 	EXPLODEXSP;
34 	return xc;
35 }
36 
37 int ieee754sp_isnan(ieee754sp x)
38 {
39 	return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
40 }
41 
42 int ieee754sp_issnan(ieee754sp x)
43 {
44 	assert(ieee754sp_isnan(x));
45 	return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
46 }
47 
48 
49 ieee754sp ieee754sp_xcpt(ieee754sp r, const char *op, ...)
50 {
51 	struct ieee754xctx ax;
52 
53 	if (!TSTX())
54 		return r;
55 
56 	ax.op = op;
57 	ax.rt = IEEE754_RT_SP;
58 	ax.rv.sp = r;
59 	va_start(ax.ap, op);
60 	ieee754_xcpt(&ax);
61 	va_end(ax.ap);
62 	return ax.rv.sp;
63 }
64 
65 ieee754sp ieee754sp_nanxcpt(ieee754sp r, const char *op, ...)
66 {
67 	struct ieee754xctx ax;
68 
69 	assert(ieee754sp_isnan(r));
70 
71 	if (!ieee754sp_issnan(r))	/* QNAN does not cause invalid op !! */
72 		return r;
73 
74 	if (!SETANDTESTCX(IEEE754_INVALID_OPERATION)) {
75 		/* not enabled convert to a quiet NaN */
76 		SPMANT(r) &= (~SP_MBIT(SP_MBITS-1));
77 		if (ieee754sp_isnan(r))
78 			return r;
79 		else
80 			return ieee754sp_indef();
81 	}
82 
83 	ax.op = op;
84 	ax.rt = 0;
85 	ax.rv.sp = r;
86 	va_start(ax.ap, op);
87 	ieee754_xcpt(&ax);
88 	va_end(ax.ap);
89 	return ax.rv.sp;
90 }
91 
92 ieee754sp ieee754sp_bestnan(ieee754sp x, ieee754sp y)
93 {
94 	assert(ieee754sp_isnan(x));
95 	assert(ieee754sp_isnan(y));
96 
97 	if (SPMANT(x) > SPMANT(y))
98 		return x;
99 	else
100 		return y;
101 }
102 
103 
104 static unsigned get_rounding(int sn, unsigned xm)
105 {
106 	/* inexact must round of 3 bits
107 	 */
108 	if (xm & (SP_MBIT(3) - 1)) {
109 		switch (ieee754_csr.rm) {
110 		case IEEE754_RZ:
111 			break;
112 		case IEEE754_RN:
113 			xm += 0x3 + ((xm >> 3) & 1);
114 			/* xm += (xm&0x8)?0x4:0x3 */
115 			break;
116 		case IEEE754_RU:	/* toward +Infinity */
117 			if (!sn)	/* ?? */
118 				xm += 0x8;
119 			break;
120 		case IEEE754_RD:	/* toward -Infinity */
121 			if (sn)	/* ?? */
122 				xm += 0x8;
123 			break;
124 		}
125 	}
126 	return xm;
127 }
128 
129 
130 /* generate a normal/denormal number with over,under handling
131  * sn is sign
132  * xe is an unbiased exponent
133  * xm is 3bit extended precision value.
134  */
135 ieee754sp ieee754sp_format(int sn, int xe, unsigned xm)
136 {
137 	assert(xm);		/* we don't gen exact zeros (probably should) */
138 
139 	assert((xm >> (SP_MBITS + 1 + 3)) == 0);	/* no execess */
140 	assert(xm & (SP_HIDDEN_BIT << 3));
141 
142 	if (xe < SP_EMIN) {
143 		/* strip lower bits */
144 		int es = SP_EMIN - xe;
145 
146 		if (ieee754_csr.nod) {
147 			SETCX(IEEE754_UNDERFLOW);
148 			SETCX(IEEE754_INEXACT);
149 
150 			switch(ieee754_csr.rm) {
151 			case IEEE754_RN:
152 			case IEEE754_RZ:
153 				return ieee754sp_zero(sn);
154 			case IEEE754_RU:      /* toward +Infinity */
155 				if(sn == 0)
156 					return ieee754sp_min(0);
157 				else
158 					return ieee754sp_zero(1);
159 			case IEEE754_RD:      /* toward -Infinity */
160 				if(sn == 0)
161 					return ieee754sp_zero(0);
162 				else
163 					return ieee754sp_min(1);
164 			}
165 		}
166 
167 		if (xe == SP_EMIN - 1
168 				&& get_rounding(sn, xm) >> (SP_MBITS + 1 + 3))
169 		{
170 			/* Not tiny after rounding */
171 			SETCX(IEEE754_INEXACT);
172 			xm = get_rounding(sn, xm);
173 			xm >>= 1;
174 			/* Clear grs bits */
175 			xm &= ~(SP_MBIT(3) - 1);
176 			xe++;
177 		}
178 		else {
179 			/* sticky right shift es bits
180 			 */
181 			SPXSRSXn(es);
182 			assert((xm & (SP_HIDDEN_BIT << 3)) == 0);
183 			assert(xe == SP_EMIN);
184 		}
185 	}
186 	if (xm & (SP_MBIT(3) - 1)) {
187 		SETCX(IEEE754_INEXACT);
188 		if ((xm & (SP_HIDDEN_BIT << 3)) == 0) {
189 			SETCX(IEEE754_UNDERFLOW);
190 		}
191 
192 		/* inexact must round of 3 bits
193 		 */
194 		xm = get_rounding(sn, xm);
195 		/* adjust exponent for rounding add overflowing
196 		 */
197 		if (xm >> (SP_MBITS + 1 + 3)) {
198 			/* add causes mantissa overflow */
199 			xm >>= 1;
200 			xe++;
201 		}
202 	}
203 	/* strip grs bits */
204 	xm >>= 3;
205 
206 	assert((xm >> (SP_MBITS + 1)) == 0);	/* no execess */
207 	assert(xe >= SP_EMIN);
208 
209 	if (xe > SP_EMAX) {
210 		SETCX(IEEE754_OVERFLOW);
211 		SETCX(IEEE754_INEXACT);
212 		/* -O can be table indexed by (rm,sn) */
213 		switch (ieee754_csr.rm) {
214 		case IEEE754_RN:
215 			return ieee754sp_inf(sn);
216 		case IEEE754_RZ:
217 			return ieee754sp_max(sn);
218 		case IEEE754_RU:	/* toward +Infinity */
219 			if (sn == 0)
220 				return ieee754sp_inf(0);
221 			else
222 				return ieee754sp_max(1);
223 		case IEEE754_RD:	/* toward -Infinity */
224 			if (sn == 0)
225 				return ieee754sp_max(0);
226 			else
227 				return ieee754sp_inf(1);
228 		}
229 	}
230 	/* gen norm/denorm/zero */
231 
232 	if ((xm & SP_HIDDEN_BIT) == 0) {
233 		/* we underflow (tiny/zero) */
234 		assert(xe == SP_EMIN);
235 		if (ieee754_csr.mx & IEEE754_UNDERFLOW)
236 			SETCX(IEEE754_UNDERFLOW);
237 		return buildsp(sn, SP_EMIN - 1 + SP_EBIAS, xm);
238 	} else {
239 		assert((xm >> (SP_MBITS + 1)) == 0);	/* no execess */
240 		assert(xm & SP_HIDDEN_BIT);
241 
242 		return buildsp(sn, xe + SP_EBIAS, xm & ~SP_HIDDEN_BIT);
243 	}
244 }
245