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Re: [PATCH 2/5] Use fabs(x) instead of branching on signedness of input to sin and cos



On 08/23/2016 08:22 PM, Siddhesh Poyarekar wrote:


@@ -181,10 +181,7 @@ do_cos_slow (mynumber u, double x, double dx, double eps, double *corp)
   cor = cor + ((cs - y) - e1 * x1);
   res = y + cor;
   cor = (y - res) + cor;
-  if (cor > 0)
-    cor = 1.0005 * cor + eps;
-  else
-    cor = 1.0005 * cor - eps;
+  cor = 1.0005 * cor + ((cor > 0) ? eps : -eps);
   *corp = cor;
   return res;


If eps is known to be >=0 then
> +  cor = 1.0005 * cor + ((cor > 0) ? eps : -eps);
might be written as
cor = 1.0005 * cor + copysign(eps, cor);
Similarly to fabs(), copysign() avoids a branch - or a potential one from the ternary.
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