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git.proxmox.com Git - wasi-libc.git/blob - libc-top-half/musl/src/math/log2f.c
1 /* origin: FreeBSD /usr/src/lib/msun/src/e_log2f.c */
3 * ====================================================
4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
6 * Developed at SunPro, a Sun Microsystems, Inc. business.
7 * Permission to use, copy, modify, and distribute this
8 * software is freely granted, provided that this notice
10 * ====================================================
13 * See comments in log2.c.
20 ivln2hi
= 1.4428710938e+00, /* 0x3fb8b000 */
21 ivln2lo
= -1.7605285393e-04, /* 0xb9389ad4 */
22 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
23 Lg1
= 0xaaaaaa.0p
-24, /* 0.66666662693 */
24 Lg2
= 0xccce13.0p
-25, /* 0.40000972152 */
25 Lg3
= 0x91e9ee.0p
-25, /* 0.28498786688 */
26 Lg4
= 0xf89e26.0p
-26; /* 0.24279078841 */
30 union {float f
; uint32_t i
;} u
= {x
};
31 float_t hfsq
,f
,s
,z
,R
,w
,t1
,t2
,hi
,lo
;
37 if (ix
< 0x00800000 || ix
>>31) { /* x < 2**-126 */
39 return -1/(x
*x
); /* log(+-0)=-inf */
41 return (x
-x
)/0.0f
; /* log(-#) = NaN */
42 /* subnormal number, scale up x */
47 } else if (ix
>= 0x7f800000) {
49 } else if (ix
== 0x3f800000)
52 /* reduce x into [sqrt(2)/2, sqrt(2)] */
53 ix
+= 0x3f800000 - 0x3f3504f3;
54 k
+= (int)(ix
>>23) - 0x7f;
55 ix
= (ix
&0x007fffff) + 0x3f3504f3;
72 lo
= f
- hi
- hfsq
+ s
*(hfsq
+R
);
73 return (lo
+hi
)*ivln2lo
+ lo
*ivln2hi
+ hi
*ivln2hi
+ k
;