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authorMarkus Armbruster <armbru@redhat.com>2017-07-27 11:46:16 +0200
committerDr. David Alan Gilbert <dgilbert@redhat.com>2017-09-06 14:38:03 +0100
commit362aaf14576d2bc3f0117b87cfb595d48cda3d64 (patch)
tree501f19735e35e5705ca87a48177181505764559f /include
parent43c64a093dbe8bffa4eb774685dee535bdffaffb (diff)
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host-utils: Simplify pow2ceil()
Cc: Radim Krčmář <rkrcmar@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com> Message-Id: <1501148776-16890-4-git-send-email-armbru@redhat.com> Reviewed-by: Eric Blake <eblake@redhat.com> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Diffstat (limited to 'include')
-rw-r--r--include/qemu/host-utils.h23
1 files changed, 14 insertions, 9 deletions
diff --git a/include/qemu/host-utils.h b/include/qemu/host-utils.h
index 6c6005f..5ac621c 100644
--- a/include/qemu/host-utils.h
+++ b/include/qemu/host-utils.h
@@ -381,18 +381,23 @@ static inline uint64_t pow2floor(uint64_t value)
return 0x8000000000000000ull >> clz64(value);
}
-/* round up to the nearest power of 2 (0 if overflow) */
+/*
+ * Return @value rounded up to the nearest power of two modulo 2^64.
+ * This is *zero* for @value > 2^63, so be careful.
+ */
static inline uint64_t pow2ceil(uint64_t value)
{
- uint8_t nlz = clz64(value);
-
- if (is_power_of_2(value)) {
- return value;
- }
- if (!nlz) {
- return 0;
+ int n = clz64(value - 1);
+
+ if (!n) {
+ /*
+ * @value - 1 has no leading zeroes, thus @value - 1 >= 2^63
+ * Therefore, either @value == 0 or @value > 2^63.
+ * If it's 0, return 1, else return 0.
+ */
+ return !value;
}
- return 1ULL << (64 - nlz);
+ return 0x8000000000000000ull >> (n - 1);
}
/**