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git.proxmox.com Git - mirror_edk2.git/blob - StdLib/LibC/Math/e_log2.c
2 /* @(#)e_log.c 1.3 95/01/18 */
4 * ====================================================
5 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
7 * Developed at SunSoft, a Sun Microsystems, Inc. business.
8 * Permission to use, copy, modify, and distribute this
9 * software is freely granted, provided that this notice
11 * ====================================================
13 #include <LibConfig.h>
14 #include <sys/EfiCdefs.h>
15 #if defined(LIBM_SCCS) && !defined(lint)
16 __RCSID("$NetBSD: e_log2.c,v 1.1 2005/07/21 12:55:58 christos Exp $");
20 #include "math_private.h"
22 #if defined(_MSC_VER) /* Handle Microsoft VC++ compiler specifics. */
23 // potential divide by 0 -- near line 53, (x-x)/zero is on purpose
24 #pragma warning ( disable : 4723 )
28 ln2
= 0.6931471805599452862268,
29 two54
= 1.80143985094819840000e+16, /* 43500000 00000000 */
30 Lg1
= 6.666666666666735130e-01, /* 3FE55555 55555593 */
31 Lg2
= 3.999999999940941908e-01, /* 3FD99999 9997FA04 */
32 Lg3
= 2.857142874366239149e-01, /* 3FD24924 94229359 */
33 Lg4
= 2.222219843214978396e-01, /* 3FCC71C5 1D8E78AF */
34 Lg5
= 1.818357216161805012e-01, /* 3FC74664 96CB03DE */
35 Lg6
= 1.531383769920937332e-01, /* 3FC39A09 D078C69F */
36 Lg7
= 1.479819860511658591e-01; /* 3FC2F112 DF3E5244 */
38 static const double zero
= 0.0;
41 __ieee754_log2(double x
)
43 double hfsq
,f
,s
,z
,R
,w
,t1
,t2
,dk
;
47 EXTRACT_WORDS(hx
,lx
,x
);
50 if (hx
< 0x00100000) { /* x < 2**-1022 */
51 if (((hx
&0x7fffffff)|lx
)==0)
52 return -two54
/zero
; /* log(+-0)=-inf */
53 if (hx
<0) return (x
-x
)/zero
; /* log(-#) = NaN */
54 k
-= 54; x
*= two54
; /* subnormal number, scale up x */
57 if (hx
>= 0x7ff00000) return x
+x
;
60 i
= (hx
+0x95f64)&0x100000;
61 SET_HIGH_WORD(x
,hx
|(i
^0x3ff00000)); /* normalize x or x/2 */
65 if((0x000fffff&(2+hx
))<3) { /* |f| < 2**-20 */
68 R
= f
*f
*(0.5-0.33333333333333333*f
);
69 return (dk
-(R
-f
)/ln2
);
76 t1
= w
*(Lg2
+w
*(Lg4
+w
*Lg6
));
77 t2
= z
*(Lg1
+w
*(Lg3
+w
*(Lg5
+w
*Lg7
)));
82 return (dk
-(hfsq
-s
*(hfsq
+R
)-f
)/ln2
);
84 return (dk
-((s
*(f
-R
))-f
)/ln2
);