Re: From bool to int: 1 or 0

From:
"mlimber" <mlimber@gmail.com>
Newsgroups:
comp.lang.c++
Date:
16 Jun 2006 11:16:47 -0700
Message-ID:
<1150481807.814409.62630@y41g2000cwy.googlegroups.com>
Frederick Gotham wrote:

In response to both Noah and mlimber,

I am not at all bothered with whether one form is easier to understand
than the other -- I am solely concerned with performance.


Different compilers (and optimizers!) will produce different code, and
some CPU architectures and memory/cache configurations may do some
things more efficiently than others. So there's really no way to
determine which is faster in general. You could use a profiler on your
particular system to see which is faster on that system, but I strongly
suspect you're barking up the old "premature optimization" tree (see,
e.g., "Beware Premature Optimization" in
http://www.gotw.ca/publications/mill09.htm).

If I wanted to simplify it, I could write a macro or a template function.

I suppose I could rephrase my question as follows:

Which of the following two macros would be preferable (performance-wise)
for use in portable code?:

    #define IncrementIfTrue(amount,true_or_false)\
        { amount += static_cast<bool>( true_or_false ); }

    #define IncrementIfTrue(amount,true_or_false)\
        { if ( true_or_false ) ++amount; }

To be used as follows:

#include <cstddef>

unsigned AmountSixes( const int *p, std::size_t const len )
{
    unsigned amount = 0;

    const T* const p_over = array + len;

    do
    {
        IncrementIfTrue( amount, *p++ == 6 );
    }
    while ( p != p_over );

    return amount;
}


First of all, macros should be avoided when possible because of all
their "issues" (see
http://www.parashift.com/c++-faq-lite/inline-functions.html#faq-9.5).

Second, using a macro or inline function or your clever code here just
obfuscates your meaning again. Write code for humans, not the CPU (let
the compiler/optimizer worry about that!), until you have measured (not
intuited!) that hand optimizing would be of significant benefit.

Cheers! --M

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