k_sin.cpp (2307B)
1 /* @(#)k_sin.c 1.3 95/01/18 */ 2 /* 3 * ==================================================== 4 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved. 5 * 6 * Developed at SunSoft, a Sun Microsystems, Inc. business. 7 * Permission to use, copy, modify, and distribute this 8 * software is freely granted, provided that this notice 9 * is preserved. 10 * ==================================================== 11 */ 12 13 //#include <sys/cdefs.h> 14 //__FBSDID("$FreeBSD$"); 15 16 /* __kernel_sin( x, y, iy) 17 * kernel sin function on ~[-pi/4, pi/4] (except on -0), pi/4 ~ 0.7854 18 * Input x is assumed to be bounded by ~pi/4 in magnitude. 19 * Input y is the tail of x. 20 * Input iy indicates whether y is 0. (if iy=0, y assume to be 0). 21 * 22 * Algorithm 23 * 1. Since sin(-x) = -sin(x), we need only to consider positive x. 24 * 2. Callers must return sin(-0) = -0 without calling here since our 25 * odd polynomial is not evaluated in a way that preserves -0. 26 * Callers may do the optimization sin(x) ~ x for tiny x. 27 * 3. sin(x) is approximated by a polynomial of degree 13 on 28 * [0,pi/4] 29 * 3 13 30 * sin(x) ~ x + S1*x + ... + S6*x 31 * where 32 * 33 * |sin(x) 2 4 6 8 10 12 | -58 34 * |----- - (1+S1*x +S2*x +S3*x +S4*x +S5*x +S6*x )| <= 2 35 * | x | 36 * 37 * 4. sin(x+y) = sin(x) + sin'(x')*y 38 * ~ sin(x) + (1-x*x/2)*y 39 * For better accuracy, let 40 * 3 2 2 2 2 41 * r = x *(S2+x *(S3+x *(S4+x *(S5+x *S6)))) 42 * then 3 2 43 * sin(x) = x + (S1*x + (x *(r-y/2)+y)) 44 */ 45 46 #include "math_private.h" 47 48 static const double 49 half = 5.00000000000000000000e-01, /* 0x3FE00000, 0x00000000 */ 50 S1 = -1.66666666666666324348e-01, /* 0xBFC55555, 0x55555549 */ 51 S2 = 8.33333333332248946124e-03, /* 0x3F811111, 0x1110F8A6 */ 52 S3 = -1.98412698298579493134e-04, /* 0xBF2A01A0, 0x19C161D5 */ 53 S4 = 2.75573137070700676789e-06, /* 0x3EC71DE3, 0x57B1FE7D */ 54 S5 = -2.50507602534068634195e-08, /* 0xBE5AE5E6, 0x8A2B9CEB */ 55 S6 = 1.58969099521155010221e-10; /* 0x3DE5D93A, 0x5ACFD57C */ 56 57 double 58 __kernel_sin(double x, double y, int iy) 59 { 60 double z,r,v,w; 61 62 z = x*x; 63 w = z*z; 64 r = S2+z*(S3+z*S4) + z*w*(S5+z*S6); 65 v = z*x; 66 if(iy==0) return x+v*(S1+z*r); 67 else return x-((z*(half*y-v*r)-y)-v*S1); 68 }