Convert ffs() != 0 callers to ctz32()

There are a number of ffs(3) callers that do roughly:

  bit = ffs(val);
  if (bit) {
      do_something(bit - 1);
  }

This pattern can be converted to ctz32() like this:

  zeroes = ctz32(val);
  if (zeroes != 32) {
      do_something(zeroes);
  }

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427124571-28598-6-git-send-email-stefanha@redhat.com
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/kvm-all.c b/kvm-all.c
index 4ec153df93..2a717e5b50 100644
--- a/kvm-all.c
+++ b/kvm-all.c
@@ -1141,18 +1141,18 @@ static int kvm_irqchip_get_virq(KVMState *s)
 {
     uint32_t *word = s->used_gsi_bitmap;
     int max_words = ALIGN(s->gsi_count, 32) / 32;
-    int i, bit;
+    int i, zeroes;
     bool retry = true;
 
 again:
     /* Return the lowest unused GSI in the bitmap */
     for (i = 0; i < max_words; i++) {
-        bit = ffs(~word[i]);
-        if (!bit) {
+        zeroes = ctz32(~word[i]);
+        if (zeroes == 32) {
             continue;
         }
 
-        return bit - 1 + i * 32;
+        return zeroes + i * 32;
     }
     if (!s->direct_msi && retry) {
         retry = false;