Convert (ffs(val) - 1) to ctz32(val)

This commit was generated mechanically by coccinelle from the following
semantic patch:

@@
expression val;
@@
- (ffs(val) - 1)
+ ctz32(val)

The call sites have been audited to ensure the ffs(0) - 1 == -1 case
never occurs (due to input validation, asserts, etc).  Therefore we
don't need to worry about the fact that ctz32(0) == 32.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-id: 1427124571-28598-5-git-send-email-stefanha@redhat.com
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/qcow2-refcount.c

@@ -2450,7 +2450,7 @@ int qcow2_pre_write_overlap_check(BlockDriverState *bs, int ign, int64_t offset,
     if (ret < 0) {
         return ret;
     } else if (ret > 0) {
-        int metadata_ol_bitnr = ffs(ret) - 1;
+        int metadata_ol_bitnr = ctz32(ret);
         assert(metadata_ol_bitnr < QCOW2_OL_MAX_BITNR);
 
         qcow2_signal_corruption(bs, true, offset, size, "Preventing invalid "

block/qcow2.c

@@ -1802,7 +1802,7 @@ static int qcow2_create2(const char *filename, int64_t total_size,
 {
     /* Calculate cluster_bits */
     int cluster_bits;
-    cluster_bits = ffs(cluster_size) - 1;
+    cluster_bits = ctz32(cluster_size);
     if (cluster_bits < MIN_CLUSTER_BITS || cluster_bits > MAX_CLUSTER_BITS ||
         (1 << cluster_bits) != cluster_size)
     {
@@ -2110,7 +2110,7 @@ static int qcow2_create(const char *filename, QemuOpts *opts, Error **errp)
         goto finish;
     }
 
-    refcount_order = ffs(refcount_bits) - 1;
+    refcount_order = ctz32(refcount_bits);
 
     ret = qcow2_create2(filename, size, backing_file, backing_fmt, flags,
                         cluster_size, prealloc, opts, version, refcount_order,

block/qed.c

@@ -436,9 +436,9 @@ static int bdrv_qed_open(BlockDriverState *bs, QDict *options, int flags,
 
     s->table_nelems = (s->header.cluster_size * s->header.table_size) /
                       sizeof(uint64_t);
-    s->l2_shift = ffs(s->header.cluster_size) - 1;
+    s->l2_shift = ctz32(s->header.cluster_size);
     s->l2_mask = s->table_nelems - 1;
-    s->l1_shift = s->l2_shift + ffs(s->table_nelems) - 1;
+    s->l1_shift = s->l2_shift + ctz32(s->table_nelems);
 
     /* Header size calculation must not overflow uint32_t */
     if (s->header.header_size > UINT32_MAX / s->header.cluster_size) {

block/rbd.c

@@ -325,7 +325,7 @@ static int qemu_rbd_create(const char *filename, QemuOpts *opts, Error **errp)
             error_setg(errp, "obj size too small");
             return -EINVAL;
         }
-        obj_order = ffs(objsize) - 1;
+        obj_order = ctz32(objsize);
     }
 
     clientname = qemu_rbd_parse_clientname(conf, clientname_buf);

block/sheepdog.c

@@ -1716,7 +1716,7 @@ static int parse_block_size_shift(BDRVSheepdogState *s, QemuOpts *opt)
         if ((object_size - 1) & object_size) {    /* not a power of 2? */
             return -EINVAL;
         }
-        obj_order = ffs(object_size) - 1;
+        obj_order = ctz32(object_size);
         if (obj_order < 20 || obj_order > 31) {
             return -EINVAL;
         }