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[v5,kvmtool,07/13] Add fls_long and roundup_pow_of_two helpers

Message ID 20180315150504.9884-8-jean-philippe.brucker@arm.com (mailing list archive)
State New, archived
Headers show

Commit Message

Jean-Philippe Brucker March 15, 2018, 3:04 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.

Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
---
Change v4->v5: new
---
 include/kvm/util.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
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Patch

diff --git a/include/kvm/util.h b/include/kvm/util.h
index 0df9f0dfdb43..4ca7aa9392b6 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);