Clarify use of and need for mffs vs. ffs

nx-X11/programs/Xserver/os/WaitFor.c

@@ -106,6 +106,8 @@ static unsigned long startTimeInMillis;
    Windows in the code */
 #define GetErrno() errno
 
+/* like ffs, but uses fd_mask instead of int as argument, so it works
+   when fd_mask is longer than an int, such as common 64-bit platforms */
 /* modifications by raphael */
 int
 mffs(fd_mask mask)
@@ -480,7 +482,7 @@ WaitForSomething(int *pClientsReady)
 	    {
 		int client_index;
 
-		curclient = ffs (clientsReadable.fds_bits[i]) - 1;
+		curclient = mffs (clientsReadable.fds_bits[i]) - 1;
 		client_index = /* raphael: modified */
 			ConnectionTranslation[curclient + (i * (sizeof(fd_mask) * 8))];
 	    pClientsReady[nready++] = client_index;

nx-X11/programs/Xserver/os/connection.c

@@ -908,7 +908,7 @@ CheckConnections(void)
 	mask = AllClients.fds_bits[i];
         while (mask)
     	{
-	    curoff = ffs (mask) - 1;
+	    curoff = mffs (mask) - 1;
 	    curclient = curoff + (i * (sizeof(fd_mask)*8));
             FD_ZERO(&tmask);
             FD_SET(curclient, &tmask);

nx-X11/programs/Xserver/os/osdep.h

@@ -218,7 +218,7 @@ extern OsCommPtr AvailableInput;
 
 extern WorkQueuePtr workQueue;
 
-/* added by raphael */
+/* in WaitFor.c */
 #define ffs mffs
 extern int mffs(fd_mask);