Delphi in a Nutshell

Name

Double Type

Syntax

type Double;

Description

The Double type is an IEEE standard floating-point type that uses 8 bytes to store a sign bit, an 11-bit exponent, and a 52-bit mantissa. The mantissa is usually normalized, that is, it has an implicit 1 bit before the most significant bit. If the exponent is zero, however, the mantissa is denormalized—without the implicit 1 bit. Thus, the numerical value of +0.0 is represented by all zero bits. An exponent of all 1 bits represents infinity (mantissa is zero) or not-a-number (mantissa is not zero).

The limits of the Double type are approximately 2.23 × 10^-308 to 1.79 × 10308, with about 15 decimal digits of precision. Table 5-1 shows the detailed format of finite and special Double values.

Table 5-1. Format of Double Floating-Point Numbers

Numeric class	Sign	Exponent Bits	Mantissa Bits
Positive
Normalized	0	0...1 to 1...10	0...0 to 1...1
Denormalized	0	0...0	0...1 to 1...1
Zero	0	0...0	0...0
Infinity	0	1...1	0...0
Signaling NaN	0	1...1	0...1 to 01...1
Quiet NaN	0	1...1	1...0 to 1...1
Negative
Normalized	1	0...1 to 1...10	0...0 to 1...1
Denormalized	1	0...0	0...1 to 1...1
Zero	1	0...0	0...0
Infinity	1	1...1	0...0
Signaling NaN	1	1...1	0...1 to 01...1
Quiet NaN	1	1...1	1...0 to 1...1

Tips and Tricks

• Double is a popular type that provides a good balance between performance and precision.

• The Double type corresponds to the double type in Java, C, and C++.

• Refer to the Intel architecture ...