Double precision

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In computing, double precision is a computer numbering format that occupies two adjacent storage locations in computer memory. A double precision number, sometimes simply called a double, may be defined to be an integer, fixed point, or floating point.

Modern computers with 32-bit storage locations use two to store a 64-bit double precision number (a single storage location can hold a single precision number). Double precision floating point is an IEEE 754 standard for encoding binary or decimal floating point numbers in 8 bytes.

IEEE 754:
16-bit: Half (binary16)
32-bit: Single (binary32), decimal32
64-bit: Double (binary64), decimal64
128-bit: Quadruple (binary128), decimal128
Other:
Minifloat ยท Extended precision
Arbitrary-precision

Contents

Double precision binary floating-point format

Double precision binary floating-point is a commonly used format on PCs, due to its wider range over single precision floating point, even if at a performance and bandwidth cost. As with single precision floating point format, it lacks precision on integer numbers when compared with an integer format of the same size. It is commonly known simply as double. The IEEE 754 standard defines a double as:

The format is written with the significand having an implicit integer bit of value 1, unless the written exponent is all zeros. With the 52 bits of the fraction significand appearing in the memory format, the total precision is therefore 53 bits (approximately 16 decimal digits, 53\log_{10}(2) \approx 15.955). The bits are laid out as follows:

IEEE 754 Double Floating Point Format.svg

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