The specific representation of floating point numbers varies from
machine to machine. Because floating point numbers are represented
internally as approximate quantities, algorithms for manipulating
floating point data often need to take account of the precise details of
the machine's floating point representation.

Some of the functions in the C library itself need this information; for
example, the algorithms for printing and reading floating point numbers
(see I/O on Streams) and for calculating trigonometric and
irrational functions (see Mathematics) use it to avoid round-off
error and loss of accuracy. User programs that implement numerical
analysis techniques also often need this information in order to
minimize or compute error bounds.

The header file float.h describes the format used by your
machine.