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/arch/mips/math-emu/ieee754sp.c

https://bitbucket.org/thekraven/iscream_thunderc-2.6.35
C | 244 lines | 166 code | 30 blank | 48 comment | 39 complexity | 6e3ae664572b0f8d4ef4245f0ed9c1cd MD5 | raw file
Possible License(s): GPL-2.0, LGPL-2.0, AGPL-1.0
  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
 30int ieee754sp_class(ieee754sp x)
 31{
 32	COMPXSP;
 33	EXPLODEXSP;
 34	return xc;
 35}
 36
 37int ieee754sp_isnan(ieee754sp x)
 38{
 39	return ieee754sp_class(x) >= IEEE754_CLASS_SNAN;
 40}
 41
 42int ieee754sp_issnan(ieee754sp x)
 43{
 44	assert(ieee754sp_isnan(x));
 45	return (SPMANT(x) & SP_MBIT(SP_MBITS-1));
 46}
 47
 48
 49ieee754sp 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
 65ieee754sp 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
 92ieee754sp 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
104static 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 */
135ieee754sp 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}