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authorEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 (GMT)
committerEric Andersen <andersen@codepoet.org>2001-11-22 14:04:29 (GMT)
commit7ce331c01ce6eb7b3f5c715a38a24359da9c6ee2 (patch)
tree3a7e8476e868ae15f4da1b7ce26b2db6f434468c /libm/k_tan.c
parentc117dd5fb183afb1a4790a6f6110d88704be6bf8 (diff)
Totally rework the math library, this time based on the MacOs X
math library (which is itself based on the math lib from FreeBSD). -Erik
Diffstat (limited to 'libm/k_tan.c')
-rw-r--r--libm/k_tan.c131
1 files changed, 131 insertions, 0 deletions
diff --git a/libm/k_tan.c b/libm/k_tan.c
new file mode 100644
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+/* @(#)k_tan.c 5.1 93/09/24 */
+/*
+ * ====================================================
+ * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
+ *
+ * Developed at SunPro, a Sun Microsystems, Inc. business.
+ * Permission to use, copy, modify, and distribute this
+ * software is freely granted, provided that this notice
+ * is preserved.
+ * ====================================================
+ */
+
+#if defined(LIBM_SCCS) && !defined(lint)
+static char rcsid[] = "$NetBSD: k_tan.c,v 1.8 1995/05/10 20:46:37 jtc Exp $";
+#endif
+
+/* __kernel_tan( x, y, k )
+ * kernel tan function on [-pi/4, pi/4], pi/4 ~ 0.7854
+ * Input x is assumed to be bounded by ~pi/4 in magnitude.
+ * Input y is the tail of x.
+ * Input k indicates whether tan (if k=1) or
+ * -1/tan (if k= -1) is returned.
+ *
+ * Algorithm
+ * 1. Since tan(-x) = -tan(x), we need only to consider positive x.
+ * 2. if x < 2^-28 (hx<0x3e300000 0), return x with inexact if x!=0.
+ * 3. tan(x) is approximated by a odd polynomial of degree 27 on
+ * [0,0.67434]
+ * 3 27
+ * tan(x) ~ x + T1*x + ... + T13*x
+ * where
+ *
+ * |tan(x) 2 4 26 | -59.2
+ * |----- - (1+T1*x +T2*x +.... +T13*x )| <= 2
+ * | x |
+ *
+ * Note: tan(x+y) = tan(x) + tan'(x)*y
+ * ~ tan(x) + (1+x*x)*y
+ * Therefore, for better accuracy in computing tan(x+y), let
+ * 3 2 2 2 2
+ * r = x *(T2+x *(T3+x *(...+x *(T12+x *T13))))
+ * then
+ * 3 2
+ * tan(x+y) = x + (T1*x + (x *(r+y)+y))
+ *
+ * 4. For x in [0.67434,pi/4], let y = pi/4 - x, then
+ * tan(x) = tan(pi/4-y) = (1-tan(y))/(1+tan(y))
+ * = 1 - 2*(tan(y) - (tan(y)^2)/(1+tan(y)))
+ */
+
+#include "math.h"
+#include "math_private.h"
+#ifdef __STDC__
+static const double
+#else
+static double
+#endif
+one = 1.00000000000000000000e+00, /* 0x3FF00000, 0x00000000 */
+pio4 = 7.85398163397448278999e-01, /* 0x3FE921FB, 0x54442D18 */
+pio4lo= 3.06161699786838301793e-17, /* 0x3C81A626, 0x33145C07 */
+T[] = {
+ 3.33333333333334091986e-01, /* 0x3FD55555, 0x55555563 */
+ 1.33333333333201242699e-01, /* 0x3FC11111, 0x1110FE7A */
+ 5.39682539762260521377e-02, /* 0x3FABA1BA, 0x1BB341FE */
+ 2.18694882948595424599e-02, /* 0x3F9664F4, 0x8406D637 */
+ 8.86323982359930005737e-03, /* 0x3F8226E3, 0xE96E8493 */
+ 3.59207910759131235356e-03, /* 0x3F6D6D22, 0xC9560328 */
+ 1.45620945432529025516e-03, /* 0x3F57DBC8, 0xFEE08315 */
+ 5.88041240820264096874e-04, /* 0x3F4344D8, 0xF2F26501 */
+ 2.46463134818469906812e-04, /* 0x3F3026F7, 0x1A8D1068 */
+ 7.81794442939557092300e-05, /* 0x3F147E88, 0xA03792A6 */
+ 7.14072491382608190305e-05, /* 0x3F12B80F, 0x32F0A7E9 */
+ -1.85586374855275456654e-05, /* 0xBEF375CB, 0xDB605373 */
+ 2.59073051863633712884e-05, /* 0x3EFB2A70, 0x74BF7AD4 */
+};
+
+#ifdef __STDC__
+ double __kernel_tan(double x, double y, int iy)
+#else
+ double __kernel_tan(x, y, iy)
+ double x,y; int iy;
+#endif
+{
+ double z,r,v,w,s;
+ int32_t ix,hx;
+ GET_HIGH_WORD(hx,x);
+ ix = hx&0x7fffffff; /* high word of |x| */
+ if(ix<0x3e300000) /* x < 2**-28 */
+ {if((int)x==0) { /* generate inexact */
+ u_int32_t low;
+ GET_LOW_WORD(low,x);
+ if(((ix|low)|(iy+1))==0) return one/fabs(x);
+ else return (iy==1)? x: -one/x;
+ }
+ }
+ if(ix>=0x3FE59428) { /* |x|>=0.6744 */
+ if(hx<0) {x = -x; y = -y;}
+ z = pio4-x;
+ w = pio4lo-y;
+ x = z+w; y = 0.0;
+ }
+ z = x*x;
+ w = z*z;
+ /* Break x^5*(T[1]+x^2*T[2]+...) into
+ * x^5(T[1]+x^4*T[3]+...+x^20*T[11]) +
+ * x^5(x^2*(T[2]+x^4*T[4]+...+x^22*[T12]))
+ */
+ r = T[1]+w*(T[3]+w*(T[5]+w*(T[7]+w*(T[9]+w*T[11]))));
+ v = z*(T[2]+w*(T[4]+w*(T[6]+w*(T[8]+w*(T[10]+w*T[12])))));
+ s = z*x;
+ r = y + z*(s*(r+v)+y);
+ r += T[0]*s;
+ w = x+r;
+ if(ix>=0x3FE59428) {
+ v = (double)iy;
+ return (double)(1-((hx>>30)&2))*(v-2.0*(x-(w*w/(w+v)-r)));
+ }
+ if(iy==1) return w;
+ else { /* if allow error up to 2 ulp,
+ simply return -1.0/(x+r) here */
+ /* compute -1.0/(x+r) accurately */
+ double a,t;
+ z = w;
+ SET_LOW_WORD(z,0);
+ v = r-(z - x); /* z+v = r+x */
+ t = a = -1.0/w; /* a = -1.0/w */
+ SET_LOW_WORD(t,0);
+ s = 1.0+t*z;
+ return t+a*(s+t*v);
+ }
+}