Re: [IDEA+RFC] Possible solution for min()/max() war

[David Lang <david.lang@digitalinsight.com>]

On Tue, 28 Aug 2001, Brad Chapman wrote:

> Mr. Lang,
>
> --- David Lang <dlang@diginsite.com> wrote:
> > Brad, the three arg min/max changes both values to the common type and
> > then compares them.
>
> 	That's the problem. It prevents you from doing varied conversions.
> My new macros allow you to do all three basic conversions (AFAICT) :
>
> 	- signed with signed
> 	- unsigned with unsigned
> 	- signed with unsigned
> 	  ^^^^^^^^^^^^^^^^^^^^
>
> 	This is the one type of conversion that the three-arg macro DOES NOT
> cover. When you provide the ability to do multiple signed/unsigned conversions
> on different sizes (signed, unsigned, long, short), then stuff becomes
> much easier.

there isn't such a thing as a signed with unsigned comparison at the
machine level (as andreas points out).

if you are thinking that there is please try and give a low level (i.e.
binary) example of how the comparison can work.

David Lang



> >
> > there isn't any need to have two different types becouse you then still
> > need to decide what the common type you are going to use for the
> > comparison is.
>
> 	What if you don't _want_ a common type? See above. IIRC, this was a major
> sticking point when Linus first changedthe macros to use a type argument; the
> new macro prevented signed/unsigned conversions. My macro defs allow that.
>
> >
> > David Lang
>
> Brad
>
> >
> >  On Tue, 28 Aug 2001, Brad Chapman wrote:
> >
> > > Date: Tue, 28 Aug 2001 12:33:17 -0700 (PDT)
> > > From: Brad Chapman <kakadu_croc@yahoo.com>
> > > To: linux-kernel@vger.kernel.org
> > > Subject: Re: [IDEA+RFC] Possible solution for min()/max() war
> > >
> > > Everyone,
> > >
> > > 	From reading this thread, I believe I have come up with several reasons,
> > > IMHO, why the old min()/max() macros were not usable:
> > >
> > > 	- They did not take into account non-typesafe comparisons
> > > 	- They were too generic
> > > 	- Some versions, IIRC, relied on typeof()
> > > 	- They did not take into account signed/unsigned conversions
> > >
> > > 	I have also discovered one problem with the new three-arg min()/max()
> > > macro: it forces both arguments to be the same, thus preventing signed/unsigned
> > > comparisons.
> > >
> > > 	Thus, I have a humble idea: add another type argument!
> > >
> > > 	Below is a coding example (just an example!):
> > >
> > > 	#define min(ta, a, tb, b)	((ta)(a) < (tb)(b) ? (a) : (b))
> > > 	#define max(ta, a, tb, b)	((ta)(a) > (tb)(b) ? (a) : (b))
> > >
> > > 	.....
> > > 	long int number[] = { 878593, 786831 };
> > > 	short int num[] = { 878, 786 };
> > >
> > > 	.....
> > > 	long_min = min(long int, num[0], long int, number[0]);
> > > 	short_min = min(short int, num[0], short int, number[0]);
> > >
> > > 	long_max = max(long int, num[1], long int, number[1]);
> > > 	short_max = max(short int, num[1], short int, number[1]);
> > >
> > > 	Thus, people can now cast different number types up or down, depending
> > > on what they need, and properly compare their sizes. The new argument also makes
> > > comparisons between signed/unsigned more flexible, because now you can cast
> > > in both directions - get a signed minimum and an unsigned minimum.
> > >
> > > 	This is an RFC. Flames, anyone? Honestly, this was one of those
> > > "lightbulb" ideas. If people object, I don't mind......
> > >
> > > Brad
> > >
> > > P.S: /me also wonders if I will need firehoses in my e-mail client ;)
> > >
> > > > On 28 Aug 2001, Andreas Schwab wrote:
> > > >
> > > > > Roman Zippel <zippel@linux-m68k.org> writes:
> > > > >
> > > > > |> Hi,
> > > > > |>
> > > > > |> Linus Torvalds wrote:
> > > > > [...]
> > > > > |> > You just fixed the "re-use arguments" bug - which is a bug, but doesn't
> > > > > |> > address the fact that most of the min/max bugs are due to the
> > programmer
> > > > > |> > _indending_ a unsigned compare because he didn't even think about the
> > > > > |> > type.
> > > >
> > > >
> > > > #if 0
> > > > If the comparison was made unsigned, cast to the largest natural
> > > > value on the target, while keeping the types and sizes of the
> > > > input variables the same, this macro does about what 99.9999999 percent
> > > > of what everybody wants:
> > > > #endif
> > > >
> > > > #include <stdio.h>
> > > >
> > > > #define min(a,b) ((size_t)(a) < (size_t)(b) ? (a) : (b))
> > > >
> > > > int main()
> > > > {
> > > >     printf("%d\n", min(1,2));
> > > >     printf("%d\n", min(-1,2));
> > > >     printf("%d\n", min(0xffffffff,3));
> > > >     printf("%d\n", min(0x8000,4));
> > > >     printf("%d\n", min(0x7fff,5));
> > > >     printf("%d\n", min(0x80000000,6));
> > > >     printf("%d\n", min(0x7fffffff,7));
> > > >
> > > >     printf("%ld\n", min(1L,2L));
> > > >     printf("%ld\n", min(-1L,2L));
> > > >     printf("%ld\n", min(0xffffffff,3L));
> > > >     printf("%ld\n", min(0x8000,4L));
> > > >     printf("%ld\n", min(0x7fff,5L));
> > > >     printf("%ld\n", min(0x80000000,6L));
> > > >     printf("%ld\n", min(0x7fffffff,7L));
> > > >
> > > >     printf("%lu\n", min(1L,2LU));
> > > >     printf("%lu\n", min(-1L,2LU));
> > > >     printf("%lu\n", min(0xffffffff,3LU));
> > > >     printf("%lu\n", min(0x8000,4LU));
> > > >     printf("%lu\n", min(0x7fff,5LU));
> > > >     printf("%lu\n", min(0x80000000,6LU));
> > > >     printf("%lu\n", min(0x7fffffff,7LU));
> > > >
> > > >     printf("%d\n", min(-1, -2));
> > > >     printf("%d\n", min(-1, 0));
> > > >     printf("%p\n", min((void *)0x80000000, (void *)0x7fffffff));
> > > >     return 0;
> > > > }
> > > >
> > > >
> > > >
> > > > Cheers,
> > > > Dick Johnson
> > > >
> > > > Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).
> > > >
> > > >     I was going to compile a list of innovations that could be
> > > >     attributed to Microsoft. Once I realized that Ctrl-Alt-Del
> > > >     was handled in the BIOS, I found that there aren't any.
> > > >
> > > >
> > > > -
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> > >
> > >
> > > =====
> > > Brad Chapman
> > >
> > > Permanent e-mail: kakadu_croc@yahoo.com
> > > Current e-mail: kakadu@adelphia.net
> > > Alternate e-mail: kakadu@netscape.net
> > >
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>
>
> =====
> Brad Chapman
>
> Permanent e-mail: kakadu_croc@yahoo.com
> Current e-mail: kakadu@adelphia.net
> Alternate e-mail: kakadu@netscape.net
>
> __________________________________________________
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