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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This archive was generated by hypermail 2b29 : Fri Aug 31 2001 - 21:00:30 EST