Autoconfiscate log2f.

Android doesn't supply log2f for us (though it does have all the other
float calls ruamoko wants).

config.d/library_functions.m4

@@ -69,3 +69,11 @@ AC_TRY_LINK(
 	AC_MSG_RESULT(no)
 )
 AM_CONDITIONAL(BUILD_GETOPT, test "x$BUILD_GETOPT" = "xyes")
+
+AC_MSG_CHECKING(for log2f)
+AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
+	[[#include <math.h>]], [float (*foo)(float) = log2f;])],
+	AC_DEFINE(HAVE_LOG2F, 1, [Define if you have log2f.])
+	[HAVE_LOG2F=yes],
+	[HAVE_LOG2F=no])
+AC_MSG_RESULT($HAVE_LOG2F)

libs/ruamoko/rua_math.c

@@ -95,7 +95,11 @@ bi_log (progs_t *pr)
 static void
 bi_log2 (progs_t *pr)
 {
+#ifdef HAVE_LOG2F
 	R_FLOAT (pr) = log2f (P_FLOAT (pr, 0));
+#else
+	R_FLOAT (pr) = logf (P_FLOAT (pr, 0)) / M_LOG2E;
+#endif
 }
 
 static void