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1 /* origin: FreeBSD /usr/src/lib/msun/src/s_log1pf.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 * ====================================================
15 const LN2_HI
: f32 = 6.9313812256e-01; /* 0x3f317180 */
16 const LN2_LO
: f32 = 9.0580006145e-06; /* 0x3717f7d1 */
17 /* |(log(1+s)-log(1-s))/s - Lg(s)| < 2**-34.24 (~[-4.95e-11, 4.97e-11]). */
18 const LG1
: f32 = 0.66666662693; /* 0xaaaaaa.0p-24 */
19 const LG2
: f32 = 0.40000972152; /* 0xccce13.0p-25 */
20 const LG3
: f32 = 0.28498786688; /* 0x91e9ee.0p-25 */
21 const LG4
: f32 = 0.24279078841; /* 0xf89e26.0p-26 */
23 #[cfg_attr(all(test, assert_no_panic), no_panic::no_panic)]
24 pub fn log1pf(x
: f32) -> f32 {
25 let mut ui
: u32 = x
.to_bits();
42 if ix
< 0x3ed413d0 || (ix
>> 31) > 0 {
47 return x
/ 0.0; /* log1p(-1)=+inf */
49 return (x
- x
) / 0.0; /* log1p(x<-1)=NaN */
51 if ix
<< 1 < 0x33800000 << 1 {
53 /* underflow if subnormal */
54 if (ix
& 0x7f800000) == 0 {
60 /* sqrt(2)/2- <= 1+x < sqrt(2)+ */
65 } else if ix
>= 0x7f800000 {
69 ui
= (1. + x
).to_bits();
71 iu
+= 0x3f800000 - 0x3f3504f3;
72 k
= (iu
>> 23) as i32 - 0x7f;
73 /* correction term ~ log(1+x)-log(u), avoid underflow in c/u */
76 1. - (f32::from_bits(ui
) - x
)
78 x
- (f32::from_bits(ui
) - 1.)
80 c
/= f32::from_bits(ui
);
84 /* reduce u into [sqrt(2)/2, sqrt(2)] */
85 iu
= (iu
& 0x007fffff) + 0x3f3504f3;
87 f
= f32::from_bits(ui
) - 1.;
92 t1
= w
* (LG2
+ w
* LG4
);
93 t2
= z
* (LG1
+ w
* LG3
);
97 s
* (hfsq
+ r
) + (dk
* LN2_LO
+ c
) - hfsq
+ f
+ dk
* LN2_HI