You most likely have a wrong config file "config.h" for the library/compiler configuration fix it.
You can confirm by defining "HAVE_LOG2F" to see if the error changes.
This is NOT a Code::Blocks problem or even likely a Compiler problem.
From math.h starting with line 562
/* 7.12.6.10 */
extern double __cdecl log2 (double);
extern float __cdecl log2f (float);
extern long double __cdecl log2l (long double);
From osdep.h http://git.videolan.org/?p=x264.git;a=blob;f=common/osdep.h;h=6249dbe0c53085167a4556ce85c4a8136abbfc90;hb=HEAD#l43 (http://git.videolan.org/?p=x264.git;a=blob;f=common/osdep.h;h=6249dbe0c53085167a4556ce85c4a8136abbfc90;hb=HEAD#l43)
43 #if !HAVE_LOG2F
44 #define log2f(x) (logf(x)/0.693147180559945f)
45 #define log2(x) (log(x)/0.693147180559945)
46 #endif
Tim S.