[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>

1 files changed, 2 insertions, 2 deletions

diff --git a/drivers/infiniband/hw/mthca/mthca_qp.c b/drivers/infiniband/hw/mthca/mthca_qp.c
index 33e3ba7937f1..d844a2569b47 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;
 	}