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Re: [PATCH] df: new option: --total (-c) to produce grand total (in the
From: |
Jim Meyering |
Subject: |
Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du) |
Date: |
Thu, 04 Sep 2008 09:32:25 +0200 |
Bruno Haible <address@hidden> wrote:
> Jim Meyering wrote:
>> Other opinions welcome.
>
> I mostly agree with Eric here: gnulib's substitute does not guarantee
> that values stored in a 'bool' are either 0 or 1, therefore the code that
> creates 'bool' values must guarantee it.
>
>> The question is how best to *maintain* the precondition in
>> the face of future development.
>
> By code inspection. We have no compiler warning for this kind of thing.
>
>>> Some of the changes (& => &&) are unconditional improvements, imho.
>
> I disagree. The & => && change inserts a conditional branch into the control
> flow, with the potential to save a single memory access. I count ca. 2 CPU
> cycles for a memory access and ca. 8 CPU cycles for a conditional jump,
> therefore I would say that the change slows down the program a bit.
Surely you are not quibbling about a few extra cycles in the run-time
of *df*. This is no hot code path. I suppose you're merely raising a
theoretical counterpoint to my absolute statement.
The benefit of using "&&" over "&" in those cases is precisely to obviate
that tedious code inspection. That benefit far outweighs the minuscule
(and probably not measurable) cost of a few extra CPU cycles in df.
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), (continued)
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Jim Meyering, 2008/09/03
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Andreas Schwab, 2008/09/03
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Jim Meyering, 2008/09/03
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Andreas Schwab, 2008/09/03
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Jim Meyering, 2008/09/03
- Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Andreas Schwab, 2008/09/03
Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Kamil Dudka, 2008/09/03
Re: [PATCH] df: new option: --total (-c) to produce grand total (in the same way as du), Eric Blake, 2008/09/03