The chords are weird. Visual Studio 2008 is developing it, but why will it be different when it is debugged and released?
int _tmain(int argc, _TCHAR* argv[])
{
for( int i = 0; i < 17; i++ )
{
int result = i * 16;
if( result > 255 )
{
result = 255;
}
printf("i:%2d, result = %3d\n", i, result) ;
}
return 0;
}
It's working as I expected in debug mode.
i: 0, result = 0
i: 1, result = 16
(...)
i:14, result = 224
i:15, result = 240
i:16, result = 255
But in the release mode, the output is weird when it's i:15.
i: 0, result = 0
i: 1, result = 16
(...)
i:14, result = 224
i:15, result = 255
i:16, result = 255
Why is this the only way to get the correct answer when you select "Optimization -> Not to optimize" in release mode?
c c++ optimization visual-studio-2008 compiler-bug
Oh, I've tried it, and in VC 2008 and 2010, debugs and releases are different It's the same on VC2012.
The command you wrote when compiling is cl/Ox vc15-bug.cpp/Fasc.
The reason why there are different results in each situation is because
This is because the for statement does not check the value of i*16 when checking the conditions, but instead writes the count and the compiler incorrectly counts.
But I don't know why the compiler made the count weird.
; 6 : for( int i = 0; i < 17; i++ )
00001 33 f6 xor esi, esi
$LL4@main:
00003 8b c6 mov eax, esi
00005 c1 e0 04 shl eax, 4
; 7 : {
; ; 8 : int result = i * 16;
; 9 :
; ; 10 : if( result > 255 )
// The original esi, 14 should be 15, not 14
00008 83 fe 0e cmp esi, 14 ; 0000000eH
0000b 7e 05 jle SHORT $LN1@main
; 11 : {
; ; 12 : result = 255;
0000d b8 ff 00 00 00 mov eax, 255 ; 000000ffH
$LN1@main:
; 13 : }
© 2024 OneMinuteCode. All rights reserved.