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3.4 The Numeric Approximation Model     continued...

The principal characteristics of a given real kind are its values for b and p and its range for e.

IEEE arithmetic is based upon a binary (b=2) representation in which p=24 (single precision), p=56 (double precision), and -127<e<127; IEEE uses what would be an exponent of -127 to represent zero and NaNs (illegal or out-of-range values). A nonbinary example is that of IBM 370 real arithmetic, in which b=16, p=6 (single precision), p=14 (double precision), and -127e127. In most implementations the main difference in the representation of different real kinds is the value of p, though it is possible (and occasionally happens) for the value of b or the range of e to vary between kinds.