Wondering how to use fabs()

[Krawlow]

Hello,

In my code I am reading from a sensor and want to check if the float value returned is out of range. In order to do so I would like to be able to calculate the absolute value of the float. Using abs() is not an option because it returns an integer: abs(-0.5) = 0

I found out the function fabs() which as I have seen on the internet, it is documented to do the abs operation with floats: fabs(-0.5) = 0.5. When using it, it does not seem to work as expected.

The following code:

float one, two;
one = 0.028;
two = -0.085;
printk("one-two=three[%d]\n",(int32_t)(one-two));
float three = one-two;
printk("three/one*100=percentage[%d]%%\n",(int32_t)(three/one*100.0));
float percentage = three/one*-100.0;
printk("abs(percentage)[%d]\n",abs(percentage));
printk("fabs(percentage)[%d]\n",(int32_t)fabs(percentage));
printk("fabs(percentage) > 400: %u\n",(fabs(percentage)> 400.0));
printk("percentage < -400: %u\n",(percentage< -400.0));
printf("%f %f\n",percentage,fabs(percentage));
return;

Gives the following output:

Hello World!
one-two=three[0]
three/one*100=percentage[403]%
abs(percentage)[403]
fabs(percentage)[-2147483648]
fabs(percentage) > 400: 0
percentage < -400: 1
-403.571411 0.000000

Hopefully I can find the answer to this. At the moment I would be able to substitute the fabs() functions for a custom made function that changes the sign if the float is negative.

Thanks,

Aleix.

[ovrebekk]

Hi Aleix

Which standard library are you using?

fabs() seems to work as expected for me when using the NEWLIB library:

CONFIG_NEWLIB_LIBC=y

What if you assign the result of the fabs operation to another variable before you print it?

Best regards
Torbjørn