[vlc-devel] [PATCH] Fix date_Increment when i_divider_den > 1

[Jean-Baptiste Kempf]

On Thu, Aug 07, 2008 at 07:39:02PM +0000, David Flynn wrote :
> From: David Flynn <davidf at rd.bbc.co.uk>
> 
> Previously, calling date_Increment(d,1) with divider_den > 1 would cause:
>  - Uncorrectable rounding error due to ordering of / followed by *
>  - Incorrect calculation of i_remainder
>  - If i_divider_num / i_divider_den is not integral, a remainder is
>    accumulated, but not divided by i_divider_num when added to date.
>  => First&last cases are evident with num=30000, den=1001.
> 
> This fixes above issues.
Applied in [8ee69aa072883ab2659e707152c11fc5ddf22777]

> 
> Signed-off-by: David Flynn <davidf at rd.bbc.co.uk>
> ---
>  src/misc/mtime.c |    9 ++++++---
>  1 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/src/misc/mtime.c b/src/misc/mtime.c
> index d9af9fd..2203034 100644
> --- a/src/misc/mtime.c
> +++ b/src/misc/mtime.c
> @@ -425,6 +425,8 @@ void date_Init( date_t *p_date, uint32_t i_divider_n, uint32_t i_divider_d )
>  
>  void date_Change( date_t *p_date, uint32_t i_divider_n, uint32_t i_divider_d )
>  {
> +    /* change time scale of remainder */
> +    p_date->i_remainder = p_date->i_remainder * i_divider_n / p_date->i_divider_num;
>      p_date->i_divider_num = i_divider_n;
>      p_date->i_divider_den = i_divider_d;
>  }
> @@ -473,14 +475,15 @@ void date_Move( date_t *p_date, mtime_t i_difference )
>   */
>  mtime_t date_Increment( date_t *p_date, uint32_t i_nb_samples )
>  {
> -    mtime_t i_dividend = (mtime_t)i_nb_samples * 1000000;
> -    p_date->date += i_dividend / p_date->i_divider_num * p_date->i_divider_den;
> +    mtime_t i_dividend = (mtime_t)i_nb_samples * 1000000 * p_date->i_divider_den;
> +    p_date->date += i_dividend / p_date->i_divider_num;
>      p_date->i_remainder += (int)(i_dividend % p_date->i_divider_num);
>  
>      if( p_date->i_remainder >= p_date->i_divider_num )
>      {
>          /* This is Bresenham algorithm. */
> -        p_date->date += p_date->i_divider_den;
> +        /* It is guaranteed that: assert(i_remainder < 2*i_divider_num) */
> +        p_date->date += 1;
>          p_date->i_remainder -= p_date->i_divider_num;
>      }
>  
> -- 
> 1.5.6
> 
> 
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-- 
Best Regards,

-- 
Jean-Baptiste Kempf
http://www.jbkempf.com/