FreeTDM: Fix "ftdm core flags/spanflags" with flag names

"x >> 1" is _NOT_ the reverse of "1 << x"...

Use code from Sean Eron Andersen's "Bit Twiddling Hacks"
(=> http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog)
to compute the log2 value (= position in the enum) of the bitflag.

This preserves the current behaviour, which is rather odd because
it is based on the position of the value in the enum, not its
actual (bit flag) value.
Signed-off-by: Stefan Knoblich <stkn@openisdn.net>

libs/freetdm/src/ftdm_io.c

@@ -4761,6 +4761,26 @@ static void print_span_flag_values(ftdm_stream_handle_t *stream)
 	}
 }
 
+/**
+ * Compute log2 of 64bit integer v
+ *
+ * Bit Twiddling Hacks
+ * http://graphics.stanford.edu/~seander/bithacks.html#IntegerLog
+ */
+static int ftdm_log2_64(uint64_t v)
+{
+	unsigned int shift;
+	uint64_t r;
+
+	r =     (v > 0xFFFFFFFF) << 5; v >>= r;
+	shift = (v > 0xFFFF    ) << 4; v >>= shift; r |= shift;
+	shift = (v > 0xFF      ) << 3; v >>= shift; r |= shift;
+	shift = (v > 0xF       ) << 2; v >>= shift; r |= shift;
+	shift = (v > 0x3       ) << 1; v >>= shift; r |= shift;
+
+	return (r | (v >> 1));
+}
+
 static char *handle_core_command(const char *cmd)
 {
 	char *mycmd = NULL;
@@ -4835,7 +4855,7 @@ static char *handle_core_command(const char *cmd)
 				print_channel_flag_values(&stream);
 				goto done;
 			}
-			flagval = flagval >> 1;
+			flagval = ftdm_log2_64(flagval);
 		} else {
 			flagval = atoi(flag);
 		}
@@ -4880,7 +4900,7 @@ static char *handle_core_command(const char *cmd)
 				print_span_flag_values(&stream);
 				goto done;
 			}
-			flagval = flagval >> 1;
+			flagval = ftdm_log2_64(flagval);
 		} else {
 			flagval = atoi(flag);
 		}