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wolf99/my_isinf.c

Last active October 27, 2019 21:50
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Portable alternative to isinf() in math.h
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my_isinf.c
int my_inf(double x)
{
volatile double tmp = x; /* Prevent optimization by compiler. */
if ((tmp == x) && ((tmp - x) != 0.0))
return x < 0.0 ? -1 : 1;
return 0;
}
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wolf99 commented Feb 2, 2017

The sum of infinity and a finite variable is still infinity. Positive and negative infinities can be differentiated by comparing them to zero. A simple test like return (x - x != 0.0); would be optimised out by most compilers, thus the need for the addition of a volatile variable. Compilers do not always implement this aspect of doubles, so testing of this function's operation is required.

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