Decimal64 floating-point format

In computing, decimal64 is a decimal floating-point computer numbering format that occupies 8 bytes (64 bits) in computer memory. It is intended for applications where it is necessary to emulate decimal rounding exactly, such as financial and tax computations.

Decimal64 supports 16 decimal digits of significand and an exponent range of −383 to +384, i.e. ±0.000000000000000×10^⁻³⁸³ to ±9.999999999999999×10^³⁸⁴. (Equivalently, ±0000000000000000×10^⁻³⁹⁸ to ±9999999999999999×10^³⁶⁹.) In contrast, the corresponding binary format, which is the most commonly used type, has an approximate range of ±0.000000000000001×10^⁻³⁰⁸ to ±1.797693134862315×10^³⁰⁸. Because the significand is not normalized, most values with less than 16 significant digits have multiple possible representations; 1 × 10²=0.1 × 10³=0.01 × 10⁴, etc. Zero has 768 possible representations (1536 if both signed zeros are included).

Decimal64 floating point is a relatively new decimal floating-point format, formally introduced in the 2008 version^[1] of IEEE 754 as well as with ISO/IEC/IEEE 60559:2011.^[2]