1 /* k_tanf.c -- float version of k_tan.c 2 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com. 3 * Optimized by Bruce D. Evans. 4 */ 5 6 /* 7 * ==================================================== 8 * Copyright 2004 Sun Microsystems, Inc. All Rights Reserved. 9 * 10 * Permission to use, copy, modify, and distribute this 11 * software is freely granted, provided that this notice 12 * is preserved. 13 * ==================================================== 14 */ 15 16 #ifndef INLINE_KERNEL_TANDF 17 #ifndef lint 18 static char rcsid[] = "$FreeBSD: src/lib/msun/src/k_tanf.c,v 1.20 2005/11/28 11:46:20 bde Exp $"; 19 #endif 20 #endif 21 22 #include "math.h" 23 #include "math_private.h" 24 25 /* |tan(x)/x - t(x)| < 2**-25.5 (~[-2e-08, 2e-08]). */ 26 static const double 27 T[] = { 28 0x15554d3418c99f.0p-54, /* 0.333331395030791399758 */ 29 0x1112fd38999f72.0p-55, /* 0.133392002712976742718 */ 30 0x1b54c91d865afe.0p-57, /* 0.0533812378445670393523 */ 31 0x191df3908c33ce.0p-58, /* 0.0245283181166547278873 */ 32 0x185dadfcecf44e.0p-61, /* 0.00297435743359967304927 */ 33 0x1362b9bf971bcd.0p-59, /* 0.00946564784943673166728 */ 34 }; 35 36 #ifdef INLINE_KERNEL_TANDF 37 extern inline 38 #endif 39 float __kernel_tandf(double x,int iy)40 __kernel_tandf(double x, int iy) 41 { 42 double z,r,w,s,t,u; 43 44 z = x*x; 45 /* 46 * Split up the polynomial into small independent terms to give 47 * opportunities for parallel evaluation. The chosen splitting is 48 * micro-optimized for Athlons (XP, X64). It costs 2 multiplications 49 * relative to Horner's method on sequential machines. 50 * 51 * We add the small terms from lowest degree up for efficiency on 52 * non-sequential machines (the lowest degree terms tend to be ready 53 * earlier). Apart from this, we don't care about order of 54 * operations, and don't need to to care since we have precision to 55 * spare. However, the chosen splitting is good for accuracy too, 56 * and would give results as accurate as Horner's method if the 57 * small terms were added from highest degree down. 58 */ 59 r = T[4]+z*T[5]; 60 t = T[2]+z*T[3]; 61 w = z*z; 62 s = z*x; 63 u = T[0]+z*T[1]; 64 r = (x+s*u)+(s*w)*(t+w*r); 65 if(iy==1) return r; 66 else return -1.0/r; 67 } 68