Re: [patch] time_after_eq fix

[George Anzinger]

Coywolf Qi Hunt wrote:
> Hello,
>
> The two macros time_after and time_after_eq were added to do wrapping
> correctly, but only time_after does it the right way, time_after_eq has
> been wrong since the very beginning(v2.1.127, 07-Nov-1998).  Now this
> patch fixes it.

I may be especially dense today, but could you give an example where your change 
actually gives a result different from what exists?

george
--
> And I don't agree with the the original code comment. I don't think this
> is gcc's fault.  If it is "a good compiler" or "a really good compiler",
> trying to be smarter than human, it wouldn't still be a C compiler.
> So I'd like it be removed.
>
> Signed-off-by: Coywolf Qi Hunt <coywolf@xxxxxxxxxx>
> ---
>
>  jiffies.h |    6 ++----
>  1 files changed, 2 insertions(+), 4 deletions(-)
>
> diff -pruN 2.6.12-rc4-mm2/include/linux/jiffies.h 2.6.12-rc4-mm2-cy/include/linux/jiffies.h
> --- 2.6.12-rc4-mm2/include/linux/jiffies.h	2005-03-03 17:12:13.000000000 +0800
> +++ 2.6.12-rc4-mm2-cy/include/linux/jiffies.h	2005-05-19 05:32:52.000000000 +0800
> @@ -102,9 +102,7 @@ static inline u64 get_jiffies_64(void)
>   *
>   * time_after(a,b) returns true if the time a is after time b.
>   *
> - * Do this with "<0" and ">=0" to only test the sign of the result. A
> - * good compiler would generate better code (and a really good compiler
> - * wouldn't care). Gcc is currently neither.
> + * Do this with "<0" and "<=0" to only test the sign of the result.
>   */
>  #define time_after(a,b)		\
>  	(typecheck(unsigned long, a) && \
> @@ -115,7 +113,7 @@ static inline u64 get_jiffies_64(void)
>  #define time_after_eq(a,b)	\
>  	(typecheck(unsigned long, a) && \
>  	 typecheck(unsigned long, b) && \
> -	 ((long)(a) - (long)(b) >= 0))
> +	 ((long)(b) - (long)(a) <= 0))
>  #define time_before_eq(a,b)	time_after_eq(b,a)
>  
>  /*
> -
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--
George Anzinger   george@xxxxxxxxxx
High-res-timers:  http://sourceforge.net/projects/high-res-timers/
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