[Numpy-discussion] Broken tMIN/tMAX macros
Sasha
ndarray at mac.com
Fri Jul 7 17:41:27 CDT 2006
Travis' recent change
<http://projects.scipy.org/scipy/numpy/changeset/2771> highlighted the
definitions of tMIN/tMAX macros.
Typed min/max were a subject for some heated discussion between Linux
kernel developers many years ago
<http://lwn.net/2001/0823/kernel.php3> that resulted in the following
definitions in the curent kernel:
"""
/*
* min()/max() macros that also do
* strict type-checking.. See the
* "unnecessary" pointer comparison.
*/
#define min(x,y) ({ \
typeof(x) _x = (x); \
typeof(y) _y = (y); \
(void) (&_x == &_y); \
_x < _y ? _x : _y; })
#define max(x,y) ({ \
typeof(x) _x = (x); \
typeof(y) _y = (y); \
(void) (&_x == &_y); \
_x > _y ? _x : _y; })
/*
* ..and if you can't take the strict
* types, you can specify one yourself.
*
* Or not use min/max at all, of course.
*/
#define min_t(type,x,y) \
({ type __x = (x); type __y = (y); __x < __y ? __x: __y; })
#define max_t(type,x,y) \
({ type __x = (x); type __y = (y); __x > __y ? __x: __y; })
"""
The idea is to force people to use _t versions unless the types of x
and y are exactly the same.
The numpy's tMIN and tMAX are clearly addressing the same problem, but
current definitions
#define tMAX(a,b,typ) {typ _x_=(a); typ _y_=(b); _x_>_y_ ? _x_ : _y_}
#define tMIN(a,b,typ) {typ _x_=(a); typ _y_=(b); _x_<_y_ ? _x_ : _y_}
are unlikely to work with any compiler. Linux kernel uses gcc trick
of wrapping a block in parenthesis to get an expression but I don't
think this is acceptable in numpy code.
Not surprizingly, these macros are not used anywhere. I propose to remove them.
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