host-utils: add ffsl

We can provide fast versions based on the other functions defined
by host-utils.h.  Some care is required on glibc, which provides
ffsl already.
Reviewed-by: NEric Blake <eblake@redhat.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

include/qemu/host-utils.h

@@ -26,6 +26,7 @@
 #define HOST_UTILS_H 1
 
 #include "qemu/compiler.h"   /* QEMU_GNUC_PREREQ */
+#include <string.h>     /* ffsl */
 
 #if defined(__x86_64__)
 #define __HAVE_FAST_MULU64__
@@ -237,4 +238,29 @@ static inline int ctpop64(uint64_t val)
 #endif
 }
 
+/* glibc does not provide an inline version of ffsl, so always define
+ * ours.  We need to give it a different name, however.
+ */
+#ifdef __GLIBC__
+#define ffsl qemu_ffsl
+#endif
+static inline int ffsl(long val)
+{
+    if (!val) {
+        return 0;
+    }
+
+#if QEMU_GNUC_PREREQ(3, 4)
+    return __builtin_ctzl(val) + 1;
+#else
+    if (sizeof(long) == 4) {
+        return ctz32(val) + 1;
+    } else if (sizeof(long) == 8) {
+        return ctz64(val) + 1;
+    } else {
+        abort();
+    }
+#endif
+}
+
 #endif