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git.proxmox.com Git - rustc.git/blob - vendor/compiler_builtins/libm/src/math/logf.rs
1 /* origin: FreeBSD /usr/src/lib/msun/src/e_logf.c */
3 * 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 * ====================================================
16 const LN2_HI
: f32 = 6.9313812256e-01; /* 0x3f317180 */
17 const LN2_LO
: f32 = 9.0580006145e-06; /* 0x3717f7d1 */
18 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
19 const LG1
: f32 = 0.66666662693; /* 0xaaaaaa.0p-24*/
20 const LG2
: f32 = 0.40000972152; /* 0xccce13.0p-25 */
21 const LG3
: f32 = 0.28498786688; /* 0x91e9ee.0p-25 */
22 const LG4
: f32 = 0.24279078841; /* 0xf89e26.0p-26 */
24 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
25 pub fn logf(mut x
: f32) -> f32 {
26 let x1p25
= f32::from_bits(0x4c000000); // 0x1p25f === 2 ^ 25
28 let mut ix
= x
.to_bits();
31 if (ix
< 0x00800000) || ((ix
>> 31) != 0) {
34 return -1. / (x
* x
); /* log(+-0)=-inf */
37 return (x
- x
) / 0.; /* log(-#) = NaN */
39 /* subnormal number, scale up x */
43 } else if ix
>= 0x7f800000 {
45 } else if ix
== 0x3f800000 {
49 /* reduce x into [sqrt(2)/2, sqrt(2)] */
50 ix
+= 0x3f800000 - 0x3f3504f3;
51 k
+= ((ix
>> 23) as i32) - 0x7f;
52 ix
= (ix
& 0x007fffff) + 0x3f3504f3;
53 x
= f32::from_bits(ix
);
59 let t1
= w
* (LG2
+ w
* LG4
);
60 let t2
= z
* (LG1
+ w
* LG3
);
62 let hfsq
= 0.5 * f
* f
;
64 s
* (hfsq
+ r
) + dk
* LN2_LO
- hfsq
+ f
+ dk
* LN2_HI