[PATCH] LOG2: Implement a general integer log2 facility in the kernel

This facility provides three entry points:

	ilog2()		Log base 2 of unsigned long
	ilog2_u32()	Log base 2 of u32
	ilog2_u64()	Log base 2 of u64

These facilities can either be used inside functions on dynamic data:

	int do_something(long q)
	{
		...;
		y = ilog2(x)
		...;
	}

Or can be used to statically initialise global variables with constant values:

	unsigned n = ilog2(27);

When performing static initialisation, the compiler will report "error:
initializer element is not constant" if asked to take a log of zero or of
something not reducible to a constant.  They treat negative numbers as
unsigned.

When not dealing with a constant, they fall back to using fls() which permits
them to use arch-specific log calculation instructions - such as BSR on
x86/x86_64 or SCAN on FRV - if available.

[akpm@osdl.org: MMC fix]
Signed-off-by: David Howells <dhowells@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: David Howells <dhowells@redhat.com>
Cc: Wojtek Kaniewski <wojtekka@toxygen.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

3 files changed, 6 insertions, 6 deletions

diff --git a/drivers/infiniband/hw/mthca/mthca_provider.c b/drivers/infiniband/hw/mthca/mthca_provider.c
index 21422a3336a..7ec7c4b937f 100644
--- a/drivers/infiniband/hw/mthca/mthca_provider.c
+++ b/drivers/infiniband/hw/mthca/mthca_provider.c
@@ -124,7 +124,7 @@ static int mthca_query_device(struct ib_device *ibdev,
 		props->max_map_per_fmr = 255;
 	else
 		props->max_map_per_fmr =
-			(1 << (32 - long_log2(mdev->limits.num_mpts))) - 1;
+			(1 << (32 - ilog2(mdev->limits.num_mpts))) - 1;
 
 	err = 0;
  out:
@@ -816,7 +816,7 @@ static int mthca_resize_cq(struct ib_cq *ibcq, int entries, struct ib_udata *uda
 		lkey = ucmd.lkey;
 	}
 
-	ret = mthca_RESIZE_CQ(dev, cq->cqn, lkey, long_log2(entries), &status);
+	ret = mthca_RESIZE_CQ(dev, cq->cqn, lkey, ilog2(entries), &status);
 	if (status)
 		ret = -EINVAL;
 
diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c
index 33e3ba7937f..d844a2569b4 100644
--- a/drivers/infiniband/hw/mthca/mthca_qp.c
+++ b/drivers/infiniband/hw/mthca/mthca_qp.c
@@ -636,11 +636,11 @@ int mthca_modify_qp(struct ib_qp *ibqp, struct ib_qp_attr *attr, int attr_mask,
 
 	if (mthca_is_memfree(dev)) {
 		if (qp->rq.max)
-			qp_context->rq_size_stride = long_log2(qp->rq.max) << 3;
+			qp_context->rq_size_stride = ilog2(qp->rq.max) << 3;
 		qp_context->rq_size_stride |= qp->rq.wqe_shift - 4;
 
 		if (qp->sq.max)
-			qp_context->sq_size_stride = long_log2(qp->sq.max) << 3;
+			qp_context->sq_size_stride = ilog2(qp->sq.max) << 3;
 		qp_context->sq_size_stride |= qp->sq.wqe_shift - 4;
 	}
 
diff --git a/drivers/infiniband/hw/mthca/mthca_srq.c b/drivers/infiniband/hw/mthca/mthca_srq.c
index 34d2c476896..10684da33d5 100644
--- a/drivers/infiniband/hw/mthca/mthca_srq.c
+++ b/drivers/infiniband/hw/mthca/mthca_srq.c
@@ -120,7 +120,7 @@ static void mthca_arbel_init_srq_context(struct mthca_dev *dev,
 
 	memset(context, 0, sizeof *context);
 
-	logsize = long_log2(srq->max);
+	logsize = ilog2(srq->max);
 	context->state_logsize_srqn = cpu_to_be32(logsize << 24 | srq->srqn);
 	context->lkey = cpu_to_be32(srq->mr.ibmr.lkey);
 	context->db_index = cpu_to_be32(srq->db_index);
@@ -213,7 +213,7 @@ int mthca_alloc_srq(struct mthca_dev *dev, struct mthca_pd *pd,
 	if (!mthca_is_memfree(dev) && (ds > dev->limits.max_desc_sz))
 		return -EINVAL;
 
-	srq->wqe_shift = long_log2(ds);
+	srq->wqe_shift = ilog2(ds);
 
 	srq->srqn = mthca_alloc(&dev->srq_table.alloc);
 	if (srq->srqn == -1)