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

2017-10-09 Thread Steven Rostedt
On Sat, 12 Aug 2017 11:30:46 -0600
Michael Sartain  wrote:

> 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.
> 

Heh, nice catch. Although the hash was never used for anything too
important. Mostly just colors of the graph.

> Signed-off-by: Michael Sartain 
> ---
>  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 & 0x);
> - tmp = (val >> 16) ^ hash;
> + tmp = ((unsigned int)val >> 16) ^ hash;

Why not just have val be unsigned int, and not do the typecast?

-- Steve

>   hash = (hash << 16) ^ tmp;
>   hash += hash >> 11;
>  



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

2017-10-09 Thread Steven Rostedt
On Sat, 12 Aug 2017 11:30:46 -0600
Michael Sartain  wrote:

> 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.
> 

Heh, nice catch. Although the hash was never used for anything too
important. Mostly just colors of the graph.

> Signed-off-by: Michael Sartain 
> ---
>  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 & 0x);
> - tmp = (val >> 16) ^ hash;
> + tmp = ((unsigned int)val >> 16) ^ hash;

Why not just have val be unsigned int, and not do the typecast?

-- Steve

>   hash = (hash << 16) ^ tmp;
>   hash += hash >> 11;
>  



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

2017-08-12 Thread Michael Sartain
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 
---
 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 & 0x);
-   tmp = (val >> 16) ^ hash;
+   tmp = ((unsigned int)val >> 16) ^ hash;
hash = (hash << 16) ^ tmp;
hash += hash >> 11;
 
-- 
2.13.2



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

2017-08-12 Thread Michael Sartain
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 
---
 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 & 0x);
-   tmp = (val >> 16) ^ hash;
+   tmp = ((unsigned int)val >> 16) ^ hash;
hash = (hash << 16) ^ tmp;
hash += hash >> 11;
 
-- 
2.13.2