A bug with float in VC6.0???
Author
Hi everyone, now listen, that is strange... I'm trying to do semothing like that:
//Declaration
float g_Alpha;
//Init.
g_Alpha = 0.3f //error
//g_Alpha = 0.1f //no error
now, suppose i want to inc., or dec that value by 0.1 when i press a key
...
case 107:
if(g_Alpha < 1.0f)
g_Alpha += 0.1f;
break;
case 109:
if(g_Alpha > 0.0f)
g_Alpha -= 0.1f;
break;
...
so, if i init the float g_alpha with 0.1f, all will work ok,
but if i init it with 0.3f or 0.5f, alpha will have a wrong value when
sub. 0.1f of g_Alpha when he is equal to 0.1f.
g_Alpha will have the value 1.49012e-008 instead of 0.
Did I missed something???
Author
How can i correct that?
if i write
if(g_Alpha > 0.0f)
g_Alpha -= 0.1f;
then g_Alpha will be set to -0.1 when this situation occur...
if i write
if(g_Alpha > 0.0f)
g_Alpha -= 0.1f;
then g_Alpha will be set to -0.1 when this situation occur...
Quote:Original post by Slug
How can i correct that?
if i write
if(g_Alpha > 0.0f)
g_Alpha -= 0.1f;
then g_Alpha will be set to -0.1 when this situation occur...
if(g_Alpha < 0.0f) g_Alpha = 0.0f;
read the link posted, floating point numbers have roundoff /trunctation errors, especially when trying to represent decimal numbers ...
you would be surprised to know that 0.1 CANNOT be respresented correctly in a floating point number. So you are really adding / subtracting a number slightly bigger or smaller than you think you are.
you would be surprised to know that 0.1 CANNOT be respresented correctly in a floating point number. So you are really adding / subtracting a number slightly bigger or smaller than you think you are.
Quote:Original post by Slug
How can i correct that?
if i write
if(g_Alpha > 0.0f)
g_Alpha -= 0.1f;
then g_Alpha will be set to -0.1 when this situation occur...
you could use an epsilon value
static const float fEpsilon = 0.001f; // change this depending on precision // desired...if( g_Alpha < EPSILON) g_Alpha = 0.0f;// or use it to see if two floating point values are close enough to each // otherif( fabs( g_Alpha - someFloat) < EPSILON) ){ // handle the situation however you want....}hth
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