ff_log2            44 libavutil/intmath.h #   define ff_log2(x) (31 - __builtin_clz((x)|1))
ff_log2            51 libavutil/intmath.h #   define ff_log2(x) (_bit_scan_reverse((x)|1))
ff_log2            62 libavutil/intmath.h #define ff_log2 ff_log2_c