diff options
| -rw-r--r-- | lib/msun/src/k_tanf.c | 28 |
1 files changed, 20 insertions, 8 deletions
diff --git a/lib/msun/src/k_tanf.c b/lib/msun/src/k_tanf.c index 8d08474..bdda30a 100644 --- a/lib/msun/src/k_tanf.c +++ b/lib/msun/src/k_tanf.c @@ -39,17 +39,29 @@ extern inline float __kernel_tandf(double x, int iy) { - double z,r,w,s; + double z,r,w,s,t,u; 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^8*T[5]) + - * x^5*(x^2*(T[2]+x^4*T[4])) - */ - r = (T[1]+w*(T[3]+w*T[5])) + z*(T[2]+w*T[4]); + /* + * Split up the polynomial into small independent terms to give + * opportunities for parallel evaluation. The chosen splitting is + * micro-optimized for Athlons (XP, X64). It costs 2 multiplications + * relative to Horner's method on sequential machines. + * + * We add the small terms from lowest degree up for efficiency on + * non-sequential machines (the lowest degree terms tend to be ready + * earlier). Apart from this, we don't care about order of + * operations, and don't need to to care since we have precision to + * spare. However, the chosen splitting is good for accuracy too, + * and would give results as accurate as Horner's method if the + * small terms were added from highest degree down. + */ + r = T[4]+z*T[5]; + t = T[2]+z*T[3]; + w = z*z; s = z*x; - r = (x+s*T[0])+(s*z)*r; + u = T[0]+z*T[1]; + r = (x+s*u)+(s*w)*(t+w*r); if(iy==1) return r; else return -1.0/r; } |
