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1da177e4 LT |
1 | /* IEEE754 floating point arithmetic |
2 | * single precision square root | |
3 | */ | |
4 | /* | |
5 | * MIPS floating point support | |
6 | * Copyright (C) 1994-2000 Algorithmics Ltd. | |
1da177e4 LT |
7 | * |
8 | * ######################################################################## | |
9 | * | |
10 | * This program is free software; you can distribute it and/or modify it | |
11 | * under the terms of the GNU General Public License (Version 2) as | |
12 | * published by the Free Software Foundation. | |
13 | * | |
14 | * This program is distributed in the hope it will be useful, but WITHOUT | |
15 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
16 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
17 | * for more details. | |
18 | * | |
19 | * You should have received a copy of the GNU General Public License along | |
20 | * with this program; if not, write to the Free Software Foundation, Inc., | |
21 | * 59 Temple Place - Suite 330, Boston MA 02111-1307, USA. | |
22 | * | |
23 | * ######################################################################## | |
24 | */ | |
25 | ||
26 | ||
27 | #include "ieee754sp.h" | |
28 | ||
29 | ieee754sp ieee754sp_sqrt(ieee754sp x) | |
30 | { | |
31 | int ix, s, q, m, t, i; | |
32 | unsigned int r; | |
33 | COMPXSP; | |
34 | ||
35 | /* take care of Inf and NaN */ | |
36 | ||
37 | EXPLODEXSP; | |
38 | CLEARCX; | |
39 | FLUSHXSP; | |
40 | ||
41 | /* x == INF or NAN? */ | |
42 | switch (xc) { | |
43 | case IEEE754_CLASS_QNAN: | |
44 | /* sqrt(Nan) = Nan */ | |
45 | return ieee754sp_nanxcpt(x, "sqrt"); | |
46 | case IEEE754_CLASS_SNAN: | |
47 | SETCX(IEEE754_INVALID_OPERATION); | |
48 | return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt"); | |
49 | case IEEE754_CLASS_ZERO: | |
50 | /* sqrt(0) = 0 */ | |
51 | return x; | |
52 | case IEEE754_CLASS_INF: | |
53 | if (xs) { | |
54 | /* sqrt(-Inf) = Nan */ | |
55 | SETCX(IEEE754_INVALID_OPERATION); | |
56 | return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt"); | |
57 | } | |
58 | /* sqrt(+Inf) = Inf */ | |
59 | return x; | |
60 | case IEEE754_CLASS_DNORM: | |
61 | case IEEE754_CLASS_NORM: | |
62 | if (xs) { | |
63 | /* sqrt(-x) = Nan */ | |
64 | SETCX(IEEE754_INVALID_OPERATION); | |
65 | return ieee754sp_nanxcpt(ieee754sp_indef(), "sqrt"); | |
66 | } | |
67 | break; | |
68 | } | |
69 | ||
70 | ix = x.bits; | |
71 | ||
72 | /* normalize x */ | |
73 | m = (ix >> 23); | |
74 | if (m == 0) { /* subnormal x */ | |
75 | for (i = 0; (ix & 0x00800000) == 0; i++) | |
76 | ix <<= 1; | |
77 | m -= i - 1; | |
78 | } | |
79 | m -= 127; /* unbias exponent */ | |
80 | ix = (ix & 0x007fffff) | 0x00800000; | |
81 | if (m & 1) /* odd m, double x to make it even */ | |
82 | ix += ix; | |
83 | m >>= 1; /* m = [m/2] */ | |
84 | ||
85 | /* generate sqrt(x) bit by bit */ | |
86 | ix += ix; | |
87 | q = s = 0; /* q = sqrt(x) */ | |
88 | r = 0x01000000; /* r = moving bit from right to left */ | |
89 | ||
90 | while (r != 0) { | |
91 | t = s + r; | |
92 | if (t <= ix) { | |
93 | s = t + r; | |
94 | ix -= t; | |
95 | q += r; | |
96 | } | |
97 | ix += ix; | |
98 | r >>= 1; | |
99 | } | |
100 | ||
101 | if (ix != 0) { | |
102 | SETCX(IEEE754_INEXACT); | |
103 | switch (ieee754_csr.rm) { | |
104 | case IEEE754_RP: | |
105 | q += 2; | |
106 | break; | |
107 | case IEEE754_RN: | |
108 | q += (q & 1); | |
109 | break; | |
110 | } | |
111 | } | |
112 | ix = (q >> 1) + 0x3f000000; | |
113 | ix += (m << 23); | |
114 | x.bits = ix; | |
115 | return x; | |
116 | } |