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3.4 The Numeric Approximation Model

Dynamic access to the numerical properties of the implementation can enable the development of portable numerically robust software. Fortran 90 provides such access through a combination of a model of the methods for approximating real values and a set of corresponding intrinsic functions for extracting model values. These intrinsic functions, of which there are a total of 16, are called the environmental inquiry (nine) and numeric manipulation (seven) intrinsic functions.

Each kind of real number is modeled by


x is the real value
s is (the sign of the value)
b is the radix (base) and is usually 2; b is constant for a given real kind
p is the base b precision; p is constant for a given real kind
e is the base b exponent of the value
is the i digit, base b, of the value; ;
may be 0 only if all are 0