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POWhich is faster : if (bool) or if(int)?
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copied!<blockquote> <p><a href="https://stackoverflow.com/questions/5554725/which-value-is-better-to-use-boolean-true-or-integer-1">Which value is better to use? Boolean true or Integer 1?</a></p> </blockquote> <p>The above topic made me do some experiments with <code>bool</code> and <code>int</code> in <code>if</code> condition. So just out of curiosity I wrote this program:</p> <pre><code>int f(int i) { if ( i ) return 99; //if(int) else return -99; } int g(bool b) { if ( b ) return 99; //if(bool) else return -99; } int main(){} </code></pre> <p><code>g++ intbool.cpp -S</code> generates asm code for each functions as follows:</p> <ul> <li><p>asm code for <code>f(int)</code></p> <pre><code>__Z1fi: LFB0: pushl %ebp LCFI0: movl %esp, %ebp LCFI1: cmpl $0, 8(%ebp) je L2 movl $99, %eax jmp L3 L2: movl $-99, %eax L3: leave LCFI2: ret </code></pre></li> <li><p>asm code for <code>g(bool)</code></p> <pre><code>__Z1gb: LFB1: pushl %ebp LCFI3: movl %esp, %ebp LCFI4: subl $4, %esp LCFI5: movl 8(%ebp), %eax movb %al, -4(%ebp) cmpb $0, -4(%ebp) je L5 movl $99, %eax jmp L6 L5: movl $-99, %eax L6: leave LCFI6: ret </code></pre></li> </ul> <p>Surprisingly, <code>g(bool)</code> generates more <code>asm</code> instructions! Does it mean that <code>if(bool)</code> is little slower than <code>if(int)</code>? I used to think <code>bool</code> is especially designed to be used in conditional statement such as <code>if</code>, so I was expecting <code>g(bool)</code> to generate less asm instructions, thereby making <code>g(bool)</code> more efficient and fast. </p> <p>EDIT:</p> <p>I'm not using any optimization flag as of now. But even absence of it, why does it generate more asm for <code>g(bool)</code> is a question for which I'm looking for a reasonable answer. I should also tell you that <code>-O2</code> optimization flag generates exactly same asm. But that isn't the question. The question is what I've asked.</p> <hr>

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