ReactOS 0.4.16-dev-226-g79f2289
cos.c File Reference

Go to the source code of this file.

Macros

#define PRECISION   9
 
#define M_PI   3.141592653589793238462643
 

Functions

double cos (double x)
 

Variables

static double cos_off_tbl [] = {0.0, -M_PI/2., 0, -M_PI/2.}
 
static double cos_sign_tbl [] = {1,-1,-1,1}
 

Macro Definition Documentation

◆ M_PI

#define M_PI   3.141592653589793238462643

Definition at line 15 of file cos.c.

◆ PRECISION

#define PRECISION   9

Definition at line 14 of file cos.c.

Function Documentation

◆ cos()

double cos ( double  x)

Definition at line 21 of file cos.c.

22{
23 int quadrant;
24 double x2, result;
25
26 /* Calculate the quadrant */
27 quadrant = (int)(x * (2./M_PI));
28
29 /* Get offset inside quadrant */
30 x = x - quadrant * (M_PI/2.);
31
32 /* Normalize quadrant to [0..3] */
33 quadrant = quadrant & 0x3;
34
35 /* Fixup value for the generic function */
36 x += cos_off_tbl[quadrant];
37
38 /* Calculate the negative of the square of x */
39 x2 = - (x * x);
40
41 /* This is an unrolled taylor series using <PRECISION> iterations
42 * Example with 4 iterations:
43 * result = 1 - x^2/2! + x^4/4! - x^6/6! + x^8/8!
44 * To save multiplications and to keep the precision high, it's performed
45 * like this:
46 * result = 1 - x^2 * (1/2! - x^2 * (1/4! - x^2 * (1/6! - x^2 * (1/8!))))
47 */
48
49 /* Start with 0, compiler will optimize this away */
50 result = 0;
51
52#if (PRECISION >= 10)
53 result += 1./(1.*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18*19*20);
54 result *= x2;
55#endif
56#if (PRECISION >= 9)
57 result += 1./(1.*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16*17*18);
58 result *= x2;
59#endif
60#if (PRECISION >= 8)
61 result += 1./(1.*2*3*4*5*6*7*8*9*10*11*12*13*14*15*16);
62 result *= x2;
63#endif
64#if (PRECISION >= 7)
65 result += 1./(1.*2*3*4*5*6*7*8*9*10*11*12*13*14);
66 result *= x2;
67#endif
68#if (PRECISION >= 6)
69 result += 1./(1.*2*3*4*5*6*7*8*9*10*11*12);
70 result *= x2;
71#endif
72#if (PRECISION >= 5)
73 result += 1./(1.*2*3*4*5*6*7*8*9*10);
74 result *= x2;
75#endif
76 result += 1./(1.*2*3*4*5*6*7*8);
77 result *= x2;
78
79 result += 1./(1.*2*3*4*5*6);
80 result *= x2;
81
82 result += 1./(1.*2*3*4);
83 result *= x2;
84
85 result += 1./(1.*2);
86 result *= x2;
87
88 result += 1;
89
90 /* Apply correct sign */
91 result *= cos_sign_tbl[quadrant];
92
93 return result;
94}
static double cos_off_tbl[]
Definition: cos.c:17
static double cos_sign_tbl[]
Definition: cos.c:18
#define M_PI
Definition: cos.c:15
unsigned int(__cdecl typeof(jpeg_read_scanlines))(struct jpeg_decompress_struct *
Definition: typeof.h:31
GLint GLint GLint GLint GLint x
Definition: gl.h:1548
GLuint64EXT * result
Definition: glext.h:11304
_In_ CLIPOBJ _In_ BRUSHOBJ _In_ LONG _In_ LONG _In_ LONG x2
Definition: winddi.h:3710

Variable Documentation

◆ cos_off_tbl

double cos_off_tbl[] = {0.0, -M_PI/2., 0, -M_PI/2.}
static

Definition at line 17 of file cos.c.

Referenced by cos().

◆ cos_sign_tbl

double cos_sign_tbl[] = {1,-1,-1,1}
static

Definition at line 18 of file cos.c.

Referenced by cos().