...one of the most highly
regarded and expertly designed C++ library projects in the
world. — Herb Sutter and Andrei
Unit of Least Precision or Unit in the Last Place is the gap between two different, but as close as possible, floating-point numbers.
Most decimal values, for example 0.1, cannot be exactly represented as floating-point values, but will be stored as the closest representable floating-point.
Functions are provided for finding adjacent greater and lesser floating-point values, and estimating the number of gaps between any two floating-point values.
The floating-point type FPT must have has a fixed number of bits in the representation. The number of bits may set at runtime, but must be the same for all numbers. For example, NTL::quad_float type (fixed 128-bit representation) or NTL::RR type (arbitrary but fixed decimal digits, default 150) but not a type that extends the representation to provide an exact representation for any number, for example XRC eXact Real in C.