1/* IEEE754 floating point arithmetic
2 * single precision square root
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
30ieee754sp ieee754sp_sqrt(ieee754sp x)
31{
32	int ix, s, q, m, t, i;
33	unsigned int r;
34	COMPXSP;
35
36	/* take care of Inf and NaN */
37
38	EXPLODEXSP;
39	CLEARCX;
40	FLUSHXSP;
41
42	/* x == INF or NAN? */
43	switch (xc) {
44	case IEEE754_CLASS_QNAN:
45		/* sqrt(Nan) = Nan */
46		return ieee754sp_nanxcpt(x, "sqrt");
47	case IEEE754_CLASS_SNAN:
48		SETCX(IEEE754_INVALID_OPERATION);
49		return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
50	case IEEE754_CLASS_ZERO:
51		/* sqrt(0) = 0 */
52		return x;
53	case IEEE754_CLASS_INF:
54		if (xs) {
55			/* sqrt(-Inf) = Nan */
56			SETCX(IEEE754_INVALID_OPERATION);
57			return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
58		}
59		/* sqrt(+Inf) = Inf */
60		return x;
61	case IEEE754_CLASS_DNORM:
62	case IEEE754_CLASS_NORM:
63		if (xs) {
64			/* sqrt(-x) = Nan */
65			SETCX(IEEE754_INVALID_OPERATION);
66			return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt");
67		}
68		break;
69	}
70
71	ix = x.bits;
72
73	/* normalize x */
74	m = (ix >> 23);
75	if (m == 0) {		/* subnormal x */
76		for (i = 0; (ix & 0x00800000) == 0; i++)
77			ix <<= 1;
78		m -= i - 1;
79	}
80	m -= 127;		/* unbias exponent */
81	ix = (ix & 0x007fffff) | 0x00800000;
82	if (m & 1)		/* odd m, double x to make it even */
83		ix += ix;
84	m >>= 1;		/* m = [m/2] */
85
86	/* generate sqrt(x) bit by bit */
87	ix += ix;
88	q = s = 0;		/* q = sqrt(x) */
89	r = 0x01000000;		/* r = moving bit from right to left */
90
91	while (r != 0) {
92		t = s + r;
93		if (t <= ix) {
94			s = t + r;
95			ix -= t;
96			q += r;
97		}
98		ix += ix;
99		r >>= 1;
100	}
101
102	if (ix != 0) {
103		SETCX(IEEE754_INEXACT);
104		switch (ieee754_csr.rm) {
105		case IEEE754_RP:
106			q += 2;
107			break;
108		case IEEE754_RN:
109			q += (q & 1);
110			break;
111		}
112	}
113	ix = (q >> 1) + 0x3f000000;
114	ix += (m << 23);
115	x.bits = ix;
116	return x;
117}
118