Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1710341

[PATCH 4/5] trace-cmd: Use unsigned values in Hsieh's trace_hash fast hash function

Show all headers | View raw

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

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

[PATCH 0/5] trace-cmd: Fixes for four small bugs plus minor cleanup Michael Sartain <mikesart@fastmail.com> - 2017-08-12 19:40 +0200
  [PATCH 1/5] trace-cmd: Fix incorrect malloc size arg: *item instead of item Michael Sartain <mikesart@fastmail.com> - 2017-08-12 19:50 +0200
  [PATCH 3/5] trace-cmd: Add ULL suffix to MISSING_EVENTS since ints shouldn't be left shifted by 31 Michael Sartain <mikesart@fastmail.com> - 2017-08-12 19:50 +0200
  [PATCH 4/5] trace-cmd: Use unsigned values in Hsieh's trace_hash fast hash function Michael Sartain <mikesart@fastmail.com> - 2017-08-12 19:50 +0200

csiph-web