Quick start manual

5-10 Delphi Language Guide
Simple types
Real types
A real type defines a set of numbers that can be represented with floating-point
notation. The table below gives the ranges and storage formats for the fundamental
real types.
The generic type Real, in its current implementation, is equivalent to Double.
Note The six-byte Real48 type was called Real in earlier versions of Object Pascal. If you are
recompiling code that uses the older, six-byte Real type in Delphi, you may want to
change it to Real48. You can also use the {$REALCOMPATIBILITY ON} compiler
directive to turn Real back into the six-byte type.
The following remarks apply to fundamental real types.
• Real48 is maintained for backward compatibility. Since its storage format is not
native to the Intel processor architecture, it results in slower performance than
other floating-point types.
• Extended offers greater precision than other real types but is less portable. Be
careful using Extended if you are creating data files to share across platforms.
•The Comp (computational) type is native to the Intel processor architecture and
represents a 64-bit integer. It is classified as a real, however, because it does not
behave like an ordinal type. (For example, you cannot increment or decrement a
Comp value.) Comp is maintained for backward compatibility only. Use the Int64
type for better performance.
• Currency is a fixed-point data type that minimizes rounding errors in monetary
calculations. It is stored as a scaled 64-bit integer with the four least significant
digits implicitly representing decimal places. When mixed with other real types in
assignments and expressions, Currency values are automatically divided or
multiplied by 10000.
Table 5.3 Fundamental real types
Type Range Significant digits Size in bytes
Real48 2.9 x 10
–39
.. 1.7 x 10
38
11–12 6
Single 1.5 x 10
–45
.. 3.4 x 10
38
7–8 4
Double 5.0 x 10
–324
.. 1.7 x 10
308
15–16 8
Extended 3.6 x 10
–4951
.. 1.1 x 10
4932
19–20 10
Comp –2
63
+1 .. 2
63
–1 19–20 8
Currency –922337203685477.5808.. 922337203685477.5807 19–20 8
Table 5.4 Generic real types
Type Range Significant digits Size in bytes
Real 5.0 x 10
–324
.. 1.7 x 10
308
15–16 8