Last change
on this file since 559 was
444,
checked in by satin@…, 6 years ago
|
add newlib,libalmos-mkh, restructure shared_syscalls.h and mini-libc
|
File size:
1.7 KB
|
Line | |
---|
1 | |
---|
2 | /* @(#)z_logarithmf.c 1.0 98/08/13 */ |
---|
3 | /****************************************************************** |
---|
4 | * The following routines are coded directly from the algorithms |
---|
5 | * and coefficients given in "Software Manual for the Elementary |
---|
6 | * Functions" by William J. Cody, Jr. and William Waite, Prentice |
---|
7 | * Hall, 1980. |
---|
8 | ******************************************************************/ |
---|
9 | /****************************************************************** |
---|
10 | * Logarithm |
---|
11 | * |
---|
12 | * Input: |
---|
13 | * x - floating point value |
---|
14 | * ten - indicates base ten numbers |
---|
15 | * |
---|
16 | * Output: |
---|
17 | * logarithm of x |
---|
18 | * |
---|
19 | * Description: |
---|
20 | * This routine calculates logarithms. |
---|
21 | * |
---|
22 | *****************************************************************/ |
---|
23 | |
---|
24 | #include "fdlibm.h" |
---|
25 | #include "zmath.h" |
---|
26 | |
---|
27 | static const float a[] = { -0.5527074855 }; |
---|
28 | static const float b[] = { -0.6632718214e+1 }; |
---|
29 | static const float C1 = 0.693145752; |
---|
30 | static const float C2 = 1.428606820e-06; |
---|
31 | static const float C3 = 0.4342944819; |
---|
32 | |
---|
33 | float |
---|
34 | logarithmf (float x, |
---|
35 | int ten) |
---|
36 | { |
---|
37 | int N; |
---|
38 | float f, w, z; |
---|
39 | |
---|
40 | /* Check for domain/range errors here. */ |
---|
41 | if (x == 0.0) |
---|
42 | { |
---|
43 | errno = ERANGE; |
---|
44 | return (-z_infinity_f.f); |
---|
45 | } |
---|
46 | else if (x < 0.0) |
---|
47 | { |
---|
48 | errno = EDOM; |
---|
49 | return (z_notanum_f.f); |
---|
50 | } |
---|
51 | else if (!isfinite(x)) |
---|
52 | { |
---|
53 | if (isnanf(x)) |
---|
54 | return (z_notanum_f.f); |
---|
55 | else |
---|
56 | return (z_infinity_f.f); |
---|
57 | } |
---|
58 | |
---|
59 | /* Get the exponent and mantissa where x = f * 2^N. */ |
---|
60 | f = frexpf (x, &N); |
---|
61 | |
---|
62 | z = f - 0.5; |
---|
63 | |
---|
64 | if (f > __SQRT_HALF) |
---|
65 | z = (z - 0.5) / (f * 0.5 + 0.5); |
---|
66 | else |
---|
67 | { |
---|
68 | N--; |
---|
69 | z /= (z * 0.5 + 0.5); |
---|
70 | } |
---|
71 | w = z * z; |
---|
72 | |
---|
73 | /* Use Newton's method with 4 terms. */ |
---|
74 | z += z * w * (a[0]) / ((w + 1.0) * w + b[0]); |
---|
75 | |
---|
76 | if (N != 0) |
---|
77 | z = (N * C2 + z) + N * C1; |
---|
78 | |
---|
79 | if (ten) |
---|
80 | z *= C3; |
---|
81 | |
---|
82 | return (z); |
---|
83 | } |
---|
Note: See
TracBrowser
for help on using the repository browser.