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Subject[PATCH 1/2] perf tools: Fix next_pow2_l()
Date
My implementation of next_pow2_l() was incorrect.
e.g.

perf record -m4296015872 uname
rounding mmap pages size to 17592186044416 bytes (4294967296 pages)
Invalid argument for --mmap_pages/-m

Notice that the next power-of-2 value 4294967296 is
less than the option value 4296015872.

Change to using __builtin_clzl() and prevent the
shift being equal to the width of the operand.
Also __builtin_clzl(x) is undefined if x is 0,
so adjust the condition to preclude that
possibility. Now:

perf record -m4296015872 uname
rounding mmap pages size to 35184372088832 bytes (8589934592 pages)
Invalid argument for --mmap_pages/-m

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
---
tools/perf/util/util.h | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/util.h b/tools/perf/util/util.h
index a1eea3e..ae609fe 100644
--- a/tools/perf/util/util.h
+++ b/tools/perf/util/util.h
@@ -284,13 +284,14 @@ static inline unsigned next_pow2(unsigned x)

static inline unsigned long next_pow2_l(unsigned long x)
{
-#if BITS_PER_LONG == 64
- if (x <= (1UL << 31))
- return next_pow2(x);
- return (unsigned long)next_pow2(x >> 32) << 32;
-#else
- return next_pow2(x);
-#endif
+ int leading_zeros;
+
+ if (x < 2)
+ return 1;
+ leading_zeros = __builtin_clzl(x - 1);
+ if (!leading_zeros)
+ return 0;
+ return 1UL << (BITS_PER_LONG - leading_zeros);
}

size_t hex_width(u64 v);
--
1.7.11.7


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