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 #include "math.h" 17 #include "math_private.h" 18 19 /* |tan(x)/x - t(x)| < 2**-25.5 (~[-2e-08, 2e-08]). */ 20 static const double 21 T[] = { 22 0x15554d3418c99f.0p-54, /* 0.333331395030791399758 */ 23 0x1112fd38999f72.0p-55, /* 0.133392002712976742718 */ 24 0x1b54c91d865afe.0p-57, /* 0.0533812378445670393523 */ 25 0x191df3908c33ce.0p-58, /* 0.0245283181166547278873 */ 26 0x185dadfcecf44e.0p-61, /* 0.00297435743359967304927 */ 27 0x1362b9bf971bcd.0p-59, /* 0.00946564784943673166728 */ 28 }; 29 30 #ifdef INLINE_KERNEL_TANDF 31 static __inline 32 #endif 33 float 34 __kernel_tandf(double x, int iy) 35 { 36 double z,r,w,s,t,u; 37 38 z = x*x; 39 /* 40 * Split up the polynomial into small independent terms to give 41 * opportunities for parallel evaluation. The chosen splitting is 42 * micro-optimized for Athlons (XP, X64). It costs 2 multiplications 43 * relative to Horner's method on sequential machines. 44 * 45 * We add the small terms from lowest degree up for efficiency on 46 * non-sequential machines (the lowest degree terms tend to be ready 47 * earlier). Apart from this, we don't care about order of 48 * operations, and don't need to care since we have precision to 49 * spare. However, the chosen splitting is good for accuracy too, 50 * and would give results as accurate as Horner's method if the 51 * small terms were added from highest degree down. 52 */ 53 r = T[4]+z*T[5]; 54 t = T[2]+z*T[3]; 55 w = z*z; 56 s = z*x; 57 u = T[0]+z*T[1]; 58 r = (x+s*u)+(s*w)*(t+w*r); 59 if(iy==1) return r; 60 else return -1.0/r; 61 } 62