Re: bug in xtime.h

[Akim Demaille]

Hi friends,

> Le 22 déc. 2019 à 21:48, Paul Eggert <address@hidden> a écrit :
> 
> On 12/22/19 3:31 AM, Bruno Haible wrote:
> 
>> diff --git a/lib/xtime.h b/lib/xtime.h
>> index 77f1c30..5e0ae89 100644
>> --- a/lib/xtime.h
>> +++ b/lib/xtime.h
>> @@ -42,12 +42,13 @@ extern "C" {
>> XTIME_INLINE xtime_t
>> xtime_make (xtime_t s, long int ns)
>> {
>> -  const long int giga = 1000 * 1000 * 1000;
>> -  s += ns / giga;
>> -  ns %= giga;
>>   return XTIME_PRECISION * s + ns;
>> }
> 
> Akim put in that code in October 2018, but I can't see the need for it 
> either. I
> installed the first attached patch to revert that, and am cc'ing this to Akim 
> to
> see why it might be needed. If it is needed, we'll need to complicate the
> overflow suppression a bit.

Well, when I installed it (b159aa5da7e1aa7abeb2f77ba644aa164d25a46d), the diff 
looked like this:

>  /* Return an extended time value that contains S seconds and NS
> -   nanoseconds, without any overflow checking.  */
> +   nanoseconds.  */
>  XTIME_INLINE xtime_t
>  xtime_make (xtime_t s, long int ns)
>  {
> +  const long int giga = 1000 * 1000 * 1000;
> +  s += ns / giga;
> +  ns %= giga;
>    if (XTIME_PRECISION == 1)
>      return s;
>    else
>      return XTIME_PRECISION * s + ns;
>  }

So the first case (one-second precision) was incorrect.

The commit Bruno refers to (xtime: Assume that the compiler supports 'long 
long') is indeed about that:

> commit 896daf273035e889c50dc5b33e74b5fb891851bc
> Author: Bruno Haible <address@hidden>
> Date:   Sun Dec 22 09:46:46 2019 +0100
> 
>     gethrxtime: Assume that the compiler supports 'long long'.
>     
>     * lib/xtime.h (xtime_t): Define to 'long long int' always.
>     (XTIME_PRECISION): Define to 1000000000 always.
> 
> @@ -57,10 +45,7 @@ xtime_make (xtime_t s, long int ns)
>    const long int giga = 1000 * 1000 * 1000;
>    s += ns / giga;
>    ns %= giga;
> -  if (XTIME_PRECISION == 1)
> -    return s;
> -  else
> -    return XTIME_PRECISION * s + ns;
> +  return XTIME_PRECISION * s + ns;
>  }

Merry xtime!