src/libm/s_cos.c
author Ryan C. Gordon <icculus@icculus.org>
Thu, 21 Apr 2016 03:16:44 -0400
changeset 11729 d1ce8396c356
parent 11683 48bcba563d9c
permissions -rw-r--r--
Initial shot at a renderer target for Apple's Metal API.

This isn't complete, but is enough to run testsprite2. It's currently
Mac-only; with a little work to figure out how to properly glue in a Metal
layer to a UIView, this will likely work on iOS, too.

This is only wired up to the configure script right now, and disabled by
default. CMake and Xcode still need their bits filled in as appropriate.
     1 /*
     2  * ====================================================
     3  * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     4  *
     5  * Developed at SunPro, a Sun Microsystems, Inc. business.
     6  * Permission to use, copy, modify, and distribute this
     7  * software is freely granted, provided that this notice
     8  * is preserved.
     9  * ====================================================
    10  */
    11 
    12 /* cos(x)
    13  * Return cosine function of x.
    14  *
    15  * kernel function:
    16  *	__kernel_sin		... sine function on [-pi/4,pi/4]
    17  *	__kernel_cos		... cosine function on [-pi/4,pi/4]
    18  *	__ieee754_rem_pio2	... argument reduction routine
    19  *
    20  * Method.
    21  *      Let S,C and T denote the sin, cos and tan respectively on
    22  *	[-PI/4, +PI/4]. Reduce the argument x to y1+y2 = x-k*pi/2
    23  *	in [-pi/4 , +pi/4], and let n = k mod 4.
    24  *	We have
    25  *
    26  *          n        sin(x)      cos(x)        tan(x)
    27  *     ----------------------------------------------------------
    28  *	    0	       S	   C		 T
    29  *	    1	       C	  -S		-1/T
    30  *	    2	      -S	  -C		 T
    31  *	    3	      -C	   S		-1/T
    32  *     ----------------------------------------------------------
    33  *
    34  * Special cases:
    35  *      Let trig be any of sin, cos, or tan.
    36  *      trig(+-INF)  is NaN, with signals;
    37  *      trig(NaN)    is that NaN;
    38  *
    39  * Accuracy:
    40  *	TRIG(x) returns trig(x) nearly rounded
    41  */
    42 
    43 #include "math_libm.h"
    44 #include "math_private.h"
    45 
    46 double cos(double x)
    47 {
    48 	double y[2],z=0.0;
    49 	int32_t n, ix;
    50 
    51     /* High word of x. */
    52 	GET_HIGH_WORD(ix,x);
    53 
    54     /* |x| ~< pi/4 */
    55 	ix &= 0x7fffffff;
    56 	if(ix <= 0x3fe921fb) return __kernel_cos(x,z);
    57 
    58     /* cos(Inf or NaN) is NaN */
    59 	else if (ix>=0x7ff00000) return x-x;
    60 
    61     /* argument reduction needed */
    62 	else {
    63 	    n = __ieee754_rem_pio2(x,y);
    64 	    switch(n&3) {
    65 		case 0: return  __kernel_cos(y[0],y[1]);
    66 		case 1: return -__kernel_sin(y[0],y[1],1);
    67 		case 2: return -__kernel_cos(y[0],y[1]);
    68 		default:
    69 		        return  __kernel_sin(y[0],y[1],1);
    70 	    }
    71 	}
    72 }
    73 libm_hidden_def(cos)