Turns out, it only needed to be degree 10!

arch/i386/unistd_ilp.h

@@ -1,6 +1,9 @@
 #ifndef _ARCH_UNISTD_ILP_H
 #define _ARCH_UNISTD_ILP_H
 
+/*
+  32-bit ISA, 32-bit int, long, pointer, and offset_t
+*/
 #define _POSIX_V6_ILP32_OFF32 1
 #define _POSIX_V7_ILP32_OFF32 1
 

math/cos.c

@@ -10,14 +10,13 @@
 
   The taylor poly is centered at pi, with a radius of
   convergence of no less than pi, making it roughly accurate 
-  between 0 and 2 * pi. The polynomial is up to x^20, so it 
-  should be pretty accurate within that range.
+  between 0 and 2 * pi. The polynomial is up to x^10, which I've
+  confirmed as being accurate being 0 and 2 * pi.
 */
 double cos(double x) {
   double pi = M_PI; /* Really, me?! -Kat */
   int temp;
   double deg_2, deg_4, deg_6, deg_8, deg_10;
-  double deg_12, deg_14, deg_16, deg_18, deg_20;
   double cosine;
   
   if(x < 0) x = -x;
@@ -44,11 +43,6 @@ double cos(double x) {
   deg_6 = deg_4 * deg_2 * 2 / (6 * 5);
   deg_8 = deg_6 * deg_2 * 2 / (8 * 7);
   deg_10 = deg_8 * deg_2 * 2 / (10 * 9);
-  deg_12 = deg_10 * deg_2 * 2 / (12 * 11);
-  deg_14 = deg_12 * deg_2 * 2 / (14 * 13);
-  deg_16 = deg_14 * deg_2 * 2 / (16 * 15);
-  deg_18 = deg_16 * deg_2 * 2 / (18 * 17);
-  deg_20 = deg_18 * deg_2 * 2 / (20 * 19);
 
   /*
      In case you aren't familiar with the theory of a Taylor
@@ -79,13 +73,8 @@ double cos(double x) {
      Plus, since we're taking advantage of cosine being an
      even function, we don't need any terms less than 0, so
      why *center* at zero and include negatives?
-     (Of course, I've not done the radius of convergence work
-      for this to find out how many degrees we need to get a
-      radius of convergence of pi, so I may have used too many
-      terms, anyways. Not that I can't reduce that...)
   */
   cosine = -1 + deg_2 - deg_4 + deg_6 - deg_8 + deg_10;
-  cosine = cosine - deg_12 + deg_14 - deg_16 + deg_18 + deg_20;
 
   return cosine;
 }