]>
git.ipfire.org Git - thirdparty/glibc.git/blob - sysdeps/ieee754/flt-32/e_logf.c
1 /* e_logf.c -- float version of e_log.c.
2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
6 * ====================================================
7 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
9 * Developed at SunPro, a Sun Microsystems, Inc. business.
10 * Permission to use, copy, modify, and distribute this
11 * software is freely granted, provided that this notice
13 * ====================================================
17 #include "math_private.h"
20 ln2_hi
= 6.9313812256e-01, /* 0x3f317180 */
21 ln2_lo
= 9.0580006145e-06, /* 0x3717f7d1 */
22 two25
= 3.355443200e+07, /* 0x4c000000 */
23 Lg1
= 6.6666668653e-01, /* 3F2AAAAB */
24 Lg2
= 4.0000000596e-01, /* 3ECCCCCD */
25 Lg3
= 2.8571429849e-01, /* 3E924925 */
26 Lg4
= 2.2222198546e-01, /* 3E638E29 */
27 Lg5
= 1.8183572590e-01, /* 3E3A3325 */
28 Lg6
= 1.5313838422e-01, /* 3E1CD04F */
29 Lg7
= 1.4798198640e-01; /* 3E178897 */
31 static const float zero
= 0.0;
34 __ieee754_logf(float x
)
36 float hfsq
,f
,s
,z
,R
,w
,t1
,t2
,dk
;
42 if (ix
< 0x00800000) { /* x < 2**-126 */
43 if (__builtin_expect((ix
&0x7fffffff)==0, 0))
44 return -two25
/(x
-x
); /* log(+-0)=-inf */
45 if (__builtin_expect(ix
<0, 0))
46 return (x
-x
)/(x
-x
); /* log(-#) = NaN */
47 k
-= 25; x
*= two25
; /* subnormal number, scale up x */
50 if (__builtin_expect(ix
>= 0x7f800000, 0)) return x
+x
;
53 i
= (ix
+(0x95f64<<3))&0x800000;
54 SET_FLOAT_WORD(x
,ix
|(i
^0x3f800000)); /* normalize x or x/2 */
57 if((0x007fffff&(15+ix
))<16) { /* |f| < 2**-20 */
59 if(k
==0) return zero
; else {dk
=(float)k
;
60 return dk
*ln2_hi
+dk
*ln2_lo
;}
62 R
= f
*f
*((float)0.5-(float)0.33333333333333333*f
);
63 if(k
==0) return f
-R
; else {dk
=(float)k
;
64 return dk
*ln2_hi
-((R
-dk
*ln2_lo
)-f
);}
72 t1
= w
*(Lg2
+w
*(Lg4
+w
*Lg6
));
73 t2
= z
*(Lg1
+w
*(Lg3
+w
*(Lg5
+w
*Lg7
)));
78 if(k
==0) return f
-(hfsq
-s
*(hfsq
+R
)); else
79 return dk
*ln2_hi
-((hfsq
-(s
*(hfsq
+R
)+dk
*ln2_lo
))-f
);
81 if(k
==0) return f
-s
*(f
-R
); else
82 return dk
*ln2_hi
-((s
*(f
-R
)-dk
*ln2_lo
)-f
);
85 strong_alias (__ieee754_logf
, __logf_finite
)