gnu.cfg: Improved configuration of ffsl() and ffsll()

cfg/gnu.cfg

@@ -1161,7 +1161,8 @@
        int ffsll(long long int i); -->
   <function name="ffsl,ffsll">
     <use-retval/>
-    <returnValue type="int"/>
+    <!-- It returns the position of the first bit set, or 0 if no bits are set in i. -->
+    <returnValue type="int">arg1==0 &amp;0</returnValue>
     <noreturn>false</noreturn>
     <leak-ignore/>
     <arg nr="1" direction="in">

test/cfg/gnu.c

@@ -22,6 +22,26 @@
 #include <sys/epoll.h>
 #endif
 
+#include <strings.h>
+
+void knownConditionTrueFalse_ffsl(long i)
+{
+    // ffs() returns the position of the first bit set, or 0 if no bits are set in i.
+    const int x = ffsl(0);
+    // cppcheck-suppress knownConditionTrueFalse
+    if (x == 0) {}
+    if (ffsl(i) == 0) {}
+}
+
+void knownConditionTrueFalse_ffsll(long long i)
+{
+    // ffs() returns the position of the first bit set, or 0 if no bits are set in i.
+    const int x = ffsll(0);
+    // cppcheck-suppress knownConditionTrueFalse
+    if (x == 0) {}
+    if (ffsll(i) == 0) {}
+}
+
 int nullPointer_semtimedop(int semid, struct sembuf *sops, size_t nsops, const struct timespec *timeout)
 {
     (void) semtimedop(semid, sops, nsops, NULL); // If the timeout argument is NULL, then semtimedop() behaves exactly like semop().

test/cfg/posix.c

@@ -31,8 +31,8 @@
 #define _XOPEN_SOURCE
 #include <wchar.h>
 #include <string.h>
-
 #include <strings.h>
+
 void knownConditionTrueFalse_ffs(int i)
 {
     // ffs() returns the position of the first bit set, or 0 if no bits are set in i.