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Subject[PATCH 4/5] trace-cmd: Use unsigned values in Hsieh's trace_hash fast hash function
Date
Signed int values were being used where the original code used uint32_t types:

http://www.azillionmonkeys.com/qed/hash.html

Right shifting negative int values has implementation-defined and left shifting
has undefined behavior.

On my platform (x86_64) right shifting was doing sign extension and filling
high bits with 1s, which is different than the original algorithm.

Signed-off-by: Michael Sartain <mikesart@fastmail.com>
---
trace-hash-local.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/trace-hash-local.h b/trace-hash-local.h
index b2a1002..b3f9b06 100644
--- a/trace-hash-local.h
+++ b/trace-hash-local.h
@@ -22,7 +22,7 @@

static inline unsigned int trace_hash(int val)
{
- int hash, tmp;
+ unsigned int hash, tmp;

hash = 12546869; /* random prime */

@@ -34,7 +34,7 @@ static inline unsigned int trace_hash(int val)
*/

hash += (val & 0xffff);
- tmp = (val >> 16) ^ hash;
+ tmp = ((unsigned int)val >> 16) ^ hash;
hash = (hash << 16) ^ tmp;
hash += hash >> 11;

--
2.13.2
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