Re: [libdrm][PATCH 1/2] random: Use unsigned long for seed

[Ian Romanick <idr@freedesktop.org>]

On 02/09/2015 01:39 PM, Jan Vesely wrote:
> This is more consistent with the rest, and avoids potential undefined
> behavior (signed overflow) in drmRandom()
> 
> Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>
> ---
>  xf86drmRandom.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
> 
> diff --git a/xf86drmRandom.c b/xf86drmRandom.c
> index ecab9e2..a084b86 100644
> --- a/xf86drmRandom.c
> +++ b/xf86drmRandom.c
> @@ -98,7 +98,7 @@ typedef struct RandomState {
>      unsigned long q;		/* m div a */
>      unsigned long r;		/* m mod a */
>      unsigned long check;
> -    long          seed;
> +    unsigned long seed;
>  } RandomState;
>  
>  #if RANDOM_MAIN
> @@ -147,13 +147,13 @@ int drmRandomDestroy(void *state)
>  unsigned long drmRandom(void *state)
>  {
>      RandomState   *s = (RandomState *)state;
> -    long          hi;
> -    long          lo;
> +    unsigned long hi;
> +    unsigned long lo;
>  
>      hi      = s->seed / s->q;
>      lo      = s->seed % s->q;
>      s->seed = s->a * lo - s->r * hi;
> -    if (s->seed <= 0) s->seed += s->m;
> +    if ((s->a * lo) <= (s->r * hi)) s->seed += s->m;

This seems like an unrelated change.

>  
>      return s->seed;
>  }
> @@ -166,7 +166,7 @@ double drmRandomDouble(void *state)
>  }
>  
>  #if RANDOM_MAIN
> -static void check_period(long seed)
> +static void check_period(unsigned long seed)
>  {
>      unsigned long count = 0;
>      unsigned long initial;
> @@ -178,7 +178,7 @@ static void check_period(long seed)
>      while (initial != drmRandom(state)) {
>  	if (!++count) break;
>      }
> -    printf("With seed of %10ld, period = %10lu (0x%08lx)\n",
> +    printf("With seed of %10lu, period = %10lu (0x%08lx)\n",
>  	   seed, count, count);
>      drmRandomDestroy(state);
>  }
> @@ -195,7 +195,7 @@ int main(void)
>      }
>      printf("After 10000 iterations: %lu (%lu expected): %s\n",
>  	   rand, state->check,
> -	   rand - state->check ? "*INCORRECT*" : "CORRECT");
> +	   rand != state->check ? "*INCORRECT*" : "CORRECT");

So does this.

>      drmRandomDestroy(state);
>  
>      printf("Checking periods...\n");
> 

_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/dri-devel