lavu/intmath: add faster clz support

This should be useful for the sofalizer filter.
Reviewed-by: Kieran Kunhya <kierank@ob-encoder.com>
Reviewed-by: Clément Bœsch <u@pkh.me>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

libavutil/intmath.h

@@ -96,6 +96,9 @@ static av_always_inline av_const int ff_log2_16bit_c(unsigned int v)
 #ifndef ff_ctzll
 #define ff_ctzll(v) __builtin_ctzll(v)
 #endif
+#ifndef ff_clz
+#define ff_clz(v) __builtin_clz(v)
+#endif
 #endif
 #endif
 
@@ -135,6 +138,21 @@ static av_always_inline av_const int ff_ctzll_c(long long v)
 }
 #endif
 
+#ifndef ff_clz
+#define ff_clz ff_clz_c
+static av_always_inline av_const unsigned ff_clz_c(unsigned x)
+{
+    unsigned i = sizeof(x) * 8;
+
+    while (x) {
+        x >>= 1;
+        i--;
+    }
+
+    return i;
+}
+#endif
+
 /**
  * @}
  */