5.4.9. Return the exponent of a number (ilogb)

int ilogb(double x);

This function returns the exponent of x, without any bias, so ilogb(1.0) would return 0, and ilogb(2.0) would return 1, and so on.

When applied to 0, ilogb returns -0x7FFFFFFF. When applied to a NaN or an infinity, ilogb returns +0x7FFFFFFF. ilogb causes no exceptions or errors.

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