lkml.org 
[lkml]   [2001]   [Aug]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [IDEA+RFC] Possible solution for min()/max() war
Date
"A month of sundays ago Patrick J. LoPresti wrote:"
> This is a MUCH nicer solution. max() is a well-defined mathematical
> concept; it is simply the larger of its two arguments, period. It is
> C's *promotion* rules that kill you, especially signed->unsigned
> promotion. So just forbid them, at least when they implicit.
>
> You can argue about whether the "differing sizes" case should be a
> BUG(), since the output will still be mathematically correct. It

To give you all something definite to look at, here's some test code:

// standard good 'ol faithful version
#define __MIN(x,y) ({\
typeof(x) _x = x; \
typeof(y) _y = y; \
_x < _y ? _x : _y ; \
})

// possible implemetation with type sanity checks - alter to taste
#define MIN(x,y) ({\
const typeof(x) _x = ~(typeof(x))0; \
const typeof(y) _y = ~(typeof(y))0; \
void MIN_BUG(); \
if (sizeof(_x) != sizeof(_y)) \
MIN_BUG(); \
if ((_x > 0 && _y < 0) || (_x < 0 && _y > 0)) \
MIN_BUG(); \
__MIN(x,y); \
})

// test code that compiles with no complaints with -O1 -Wall
int main() {
unsigned i = 1;
unsigned j = -2;
return MIN(i,j);
}

// test code that complains at link time (in this version) with ..
// gcc -o test -O1 -Wall test.c
// /tmp/cczJbwv5.o: In function `main':
// /tmp/cczJbwv5.o(.text+0x7): undefined reference to `MIN_BUG'
// collect2: ld returned 1 exit status
//
int main() {
unsigned i = 1;
signed j = -2;
return MIN(i,j);
}

> depends on how often it is useful to compare (say) unsigned chars
> against ints, and on whether the compiler warns about cases where you
> try to stuff the return value into a too-small container. I bet that
> just forbidding signed->unsigned promotion would be enough.

Possibly. I have little clue as to the real extent of the problem.

Peter
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:01    [W:0.169 / U:0.120 seconds]
©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site