Home » U++ Library support » U++ Core » Defs.h minmax() change/fix
| Defs.h minmax() change/fix [message #24061] |
Wed, 23 December 2009 19:31  |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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hi there
in Defs.h:214
why not using
template <class T>
inline const T& minmax(const T& x, const T& _min, const T& _max) { return min(max(x, _min), _max); }
instead of
template <class T>
inline T minmax(T x, T _min, T _max) { return min(max(x, _min), _max); }
which is sort of logically semantics
especially when you consider the other related templates:
template <class T> inline const T& min(const T& a, const T& b) { return a < b ? a : b; }
template <class T> inline const T& max(const T& a, const T& b) { return a > b ? a : b; }
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| Re: Defs.h minmax() change/fix [message #24069 is a reply to message #24061] |
Thu, 24 December 2009 10:58  |
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mirek
Messages: 13975
Registered: November 2005
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Ultimate Member |
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| kohait00 wrote on Wed, 23 December 2009 13:31 |
hi there
in Defs.h:214
why not using
template <class T>
inline const T& minmax(const T& x, const T& _min, const T& _max) { return min(max(x, _min), _max); }
instead of
template <class T>
inline T minmax(T x, T _min, T _max) { return min(max(x, _min), _max); }
which is sort of logically semantics
especially when you consider the other related templates:
template <class T> inline const T& min(const T& a, const T& b) { return a < b ? a : b; }
template <class T> inline const T& max(const T& a, const T& b) { return a > b ? a : b; }
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What if min / max for T is defined returning temporary?
Foo min(const Foo& a, const Foo& b);
then you would be returning reference to temporary....
Well, maybe this is not really strong argument as min/max are rarely defined directly - OTOH compilers are really goot at optimizing, so practical differences in code generated are, I believe, unlikely.
That said, proposed change would be nice if type does not have copy.
I am sort of undecided, but current minmax worked fine for 10 years, I guess there is not a strong incentive to change now.
Mirek
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| Re: Defs.h minmax() change/fix [message #25325 is a reply to message #24069] |
Wed, 17 February 2010 10:24 |
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kohait00
Messages: 939
Registered: July 2009
Location: Germany
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Experienced Contributor |
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yiy are right, the compiler warns
warning C4172: returning address of local variable or temporary
using a
s = min(max(a, b), c);
//instead of
s = minmax(a, b, c);
does not produce this warning. i still dont get why.
maybe to have a
#define minmax(x, _min, max) min(max(x, _min), _max)
is a choice.
or at least
template <class T>
inline T minmax(const T& x, const T& _min, const T& _max) { return min(max(x, _min), _max); }
reducing the need of object copy by 60%  (roughly)
dont know it this is that much of speed saving, but using refs instead of temp copies is better anyway, isnt it?
[Updated on: Wed, 17 February 2010 10:25] Report message to a moderator |
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| Re: Defs.h minmax() change/fix [message #25373 is a reply to message #25325] |
Fri, 19 February 2010 16:52 |
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mirek
Messages: 13975
Registered: November 2005
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Ultimate Member |
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| kohait00 wrote on Wed, 17 February 2010 04:24 |
yiy are right, the compiler warns
warning C4172: returning address of local variable or temporary
using a
s = min(max(a, b), c);
//instead of
s = minmax(a, b, c);
does not produce this warning. i still dont get why.
maybe to have a
#define minmax(x, _min, max) min(max(x, _min), _max)
is a choice.
or at least
template <class T>
inline T minmax(const T& x, const T& _min, const T& _max) { return min(max(x, _min), _max); }
reducing the need of object copy by 60% (roughly)
dont know it this is that much of speed saving, but using refs instead of temp copies is better anyway, isnt it?
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In this case, I believe there will be no difference in code generated in most cases. It is inline after all. And in fact, it is used on fundamental types 90% of time.
Mirek
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