swap macro done strange
Author
i was browsing some code i somehow got (i don''t remember how, but i think it was a tutorial source) and i found this macro definition.
#define SWAP(A,B) { (A) ^= (B); (B) ^= (A); (A) ^= (B); }
I had never seen a swap implemented this way before and I was wondering if anyone here had. Also wondering if you think it will be more effective then a simple templated inline Swap function in terms of speed?
Thanks
There was a topic addressing this several days ago. Search for it.
How appropriate. You fight like a cow.
How appropriate. You fight like a cow.
I''ve seen it. If I recall correctly, I found it to be slower than the "standard" swap method. If you really want to know for sure, do your own tests.
The x86 CPU has a XCHG (exchange) instruction.
Do not to try to be too clever.
And C++ does have a standard std::swap() function.
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Do not to try to be too clever.
And C++ does have a standard std::swap() function.
[ Start Here ! | How To Ask Smart Questions | Recommended C++ Books | C++ FAQ Lite | Function Ptrs | CppTips Archive ]
[ Header Files | File Format Docs | LNK2001 | C++ STL Doc | STLPort | Free C++ IDE | Boost C++ Lib | MSVC6 Lib Fixes ]
Author
thanks. Also, i found some other odd functions there:
#define BIG_NUM ((double)1.5 * (double)(1 << 26) * (double)(1 << 26))
inline int
Round(double a)
{
a += BIG_NUM;
return *(int*)(&a);
}
inline int
Trunc(double a)
{
a += BIG_NUM - 0.5;
return *(int*)(&a);
}
why not for trunc just do:
inline int trunc(double a)
{
return (int) a;
}
and for round:
inline int round(double a)
{
return (int) (a + .5f);
}
do you think there''s a reason behind the way he did it above?
#define BIG_NUM ((double)1.5 * (double)(1 << 26) * (double)(1 << 26))
inline int
Round(double a)
{
a += BIG_NUM;
return *(int*)(&a);
}
inline int
Trunc(double a)
{
a += BIG_NUM - 0.5;
return *(int*)(&a);
}
why not for trunc just do:
inline int trunc(double a)
{
return (int) a;
}
and for round:
inline int round(double a)
{
return (int) (a + .5f);
}
do you think there''s a reason behind the way he did it above?
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