Tossed in some SDL_asserts to make static analyzer happier.

(Most of its complaints here are that these ints can be negative, although
they wouldn't been in sane cases. Checking sanity is what assertions do, and
it placates the analyzer appropriately.)

src/libm/k_rem_pio2.c

@@ -134,6 +134,8 @@ static const char rcsid[] =
 #include "math_libm.h"
 #include "math_private.h"
 
+#include "SDL_assert.h"
+
 libm_hidden_proto(scalbn)
     libm_hidden_proto(floor)
 #ifdef __STDC__
@@ -181,10 +183,13 @@ __kernel_rem_pio2(x, y, e0, nx, prec, ipio2)
     double z, fw, f[20], fq[20], q[20];
 
     /* initialize jk */
+    SDL_assert((prec >= 0) && (prec < SDL_arraysize(init_jk)));
     jk = init_jk[prec];
+    SDL_assert((jk >= 2) && (jk <= 6));
     jp = jk;
 
     /* determine jx,jv,q0, note that 3>q0 */
+    SDL_assert(nx > 0);
     jx = nx - 1;
     jv = (e0 - 3) / 24;
     if (jv < 0)