1 /* e_logf.c -- float version of e_log.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
3 * adapted for log2 by Ulrich Drepper <drepper@cygnus.com>
7 * ====================================================
8 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
10 * Developed at SunPro, a Sun Microsystems, Inc. business.
11 * Permission to use, copy, modify, and distribute this
12 * software is freely granted, provided that this notice
14 * ====================================================
19 #include <math_private.h>
20 #include <fix-int-fp-convert-zero.h>
23 ln2
= 0.69314718055994530942,
24 two25
= 3.355443200e+07, /* 0x4c000000 */
25 Lg1
= 6.6666668653e-01, /* 3F2AAAAB */
26 Lg2
= 4.0000000596e-01, /* 3ECCCCCD */
27 Lg3
= 2.8571429849e-01, /* 3E924925 */
28 Lg4
= 2.2222198546e-01, /* 3E638E29 */
29 Lg5
= 1.8183572590e-01, /* 3E3A3325 */
30 Lg6
= 1.5313838422e-01, /* 3E1CD04F */
31 Lg7
= 1.4798198640e-01; /* 3E178897 */
33 static const float zero
= 0.0;
36 __ieee754_log2f(float x
)
38 float hfsq
,f
,s
,z
,R
,w
,t1
,t2
,dk
;
44 if (ix
< 0x00800000) { /* x < 2**-126 */
45 if (__builtin_expect((ix
&0x7fffffff)==0, 0))
46 return -two25
/(x
-x
); /* log(+-0)=-inf */
47 if (__builtin_expect(ix
<0, 0))
48 return (x
-x
)/(x
-x
); /* log(-#) = NaN */
49 k
-= 25; x
*= two25
; /* subnormal number, scale up x */
52 if (__builtin_expect(ix
>= 0x7f800000, 0)) return x
+x
;
55 i
= (ix
+(0x95f64<<3))&0x800000;
56 SET_FLOAT_WORD(x
,ix
|(i
^0x3f800000)); /* normalize x or x/2 */
60 if((0x007fffff&(15+ix
))<16) { /* |f| < 2**-20 */
63 if (FIX_INT_FP_CONVERT_ZERO
&& dk
== 0.0f
)
67 R
= f
*f
*((float)0.5-(float)0.33333333333333333*f
);
75 t1
= w
*(Lg2
+w
*(Lg4
+w
*Lg6
));
76 t2
= z
*(Lg1
+w
*(Lg3
+w
*(Lg5
+w
*Lg7
)));
81 return dk
-((hfsq
-(s
*(hfsq
+R
)))-f
)/ln2
;
83 return dk
-((s
*(f
-R
))-f
)/ln2
;
86 strong_alias (__ieee754_log2f
, __log2f_finite
)