[v6,kvmtool,07/13] Add fls_long and roundup_pow_of_two helpers

Commit Message

Jean-Philippe Brucker June 18, 2018, 6:42 p.m. UTC

It's always nice to have a log2 handy, and the vfio-pci code will need to
perform power of two allocation from an arbitrary size. Add fls_long and
roundup_pow_of_two, based on the GCC builtin.

Reviewed-by: Punit Agrawal <[e-mail]>
Signed-off-by: Jean-Philippe Brucker <[e-mail]>
---
 include/kvm/util.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

Patch

diff --git a/include/kvm/util.h b/include/kvm/util.h
index 0df9f0dfd..4ca7aa939 100644
--- a/include/kvm/util.h
+++ b/include/kvm/util.h
@@ -90,6 +90,20 @@  static inline void msleep(unsigned int msecs)
 	usleep(MSECS_TO_USECS(msecs));
 }
 
+/*
+ * Find last (most significant) bit set. Same implementation as Linux:
+ * fls(0) = 0, fls(1) = 1, fls(1UL << 63) = 64
+ */
+static inline int fls_long(unsigned long x)
+{
+	return x ? sizeof(x) * 8 - __builtin_clzl(x) : 0;
+}
+
+static inline unsigned long roundup_pow_of_two(unsigned long x)
+{
+	return x ? 1UL << fls_long(x - 1) : 0;
+}
+
 struct kvm;
 void *mmap_hugetlbfs(struct kvm *kvm, const char *htlbfs_path, u64 size);
 void *mmap_anon_or_hugetlbfs(struct kvm *kvm, const char *hugetlbfs_path, u64 size);