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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.
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^-35 .. 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 |
The generic type Real, in its current implementation, is equivalent to Double.
Type
|
Range |
Significant digits |
Size
in bytes |
|
Real |
5.0 x 10^-324 .. 1.7 x 10^308 |
15~16 |
8 |
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, you may want to change it to Real48. You can also use the {$REALCOMPATIBILITY
ON} compiler directive to turn Real back into the six-byte type.
The
following remarks apply to fundamental real types.
· Real48 is maintained for backward
compatibility. Since its storage format is not native to the Intel CPU family,
it results in slower performance than other floating-point types.
· Extended offers greater precision than
other real types but is less portable. Be careful using Extended if you
are creating data files to share across platforms.
· The Comp (computational) type is native to the Intel CPU and
represents a 64-bit integer. It is classified as a real, however, because it
does not behave like an ordinal type. (For example, you cannot increment or
decrement a Comp value.) Comp is maintained for backward
compatibility only. Use the Int64 type for better performance.
· Currency is a fixed-point data type that minimizes rounding errors in monetary calculations. It is stored as a scaled 64-bit integer with the four least-significant digits implicitly representing decimal places. When mixed with other real types in assignments and expressions, Currency values are automatically divided or multiplied by 10000.
See also
译文
实数类型
实数类型定义了可以用浮点符号表示的数的集合。下表给出了基本实数类型的范围和存储格式：
类型
|
范围 |
精度 |
占字节数 |
|
Real48 |
2.9 x 10^-39 .. 1.7 x 10^38 |
11~12 |
6 |
|
Single |
1.5 x 10^-35 .. 3.4 x 10^38 |
7~8 |
4 |
|
Double |
5.0 x 10^-324 .. 1.7 x 10^308 |
15~16 |
8 |
|
Extended |
3.6 x 10^-4951 .. 1.1 x 10^4932 |
19~20 |
10 |
|
Comp |
-2^63+1 .. 2^63-1 |
19~20 |
8 |
|
Currency |
-922337203685477.5808 .. 922337203685477.5807 |
19~20 |
8 |
一般类型Real，在当前Object Pascal实现中等价于Double。
类型
|
范围 |
精度 |
占字节数 |
|
Real |
5.0 x 10^-324 .. 1.7 x 10^308 |
15~16 |
8 |
注意：六字节的Real48类型在Object Pascal较早的版本中叫做Real。重新编译使用了六字节Real类型的较早代码时，你也许想将其改成Real48。此时也可以用编译指示{$REALCOMPATIBILITY
ON}将Real类型转回到六字节类型。
下列注释适用于基本实数类型：
· Real48类型维持着向后兼容（向较早的版本兼容）。该类型的存储格式并非出自Intel CPU系列，因此相对其他浮点类型来说，其执行效率较慢。
· Extended比其它实数类型提供了更高的精度，但同时也占用较多的空间。当要创建跨平台共享是数据文件时，应谨慎使用该类型。
· Comp类型来自Intel CPU，表示64位的整数。将其作为实数归类，是因为该类型不具备序数类型的一些特征（如，不能对Comp值进行递增或递减）。Comp类型仅用于向后兼容，因此在新的代码中应当使用Int64类型以获得更好的性能。
· Curreny是定点数据类型，该类型在货币计算时使舍入误差最小。Currency类型以含格式的64位整数存储，其中隐含地包括了表示小数部分的4位最少有效数字。在赋值语句和表达式中将该类型与其他实数类型混合时，Currency类型的值会自动被除以或乘以10000。（大多数货币数字都只含有2位小数，Currency类型总是保留4位小数，这就足以使货币计算的误差降到最小。）
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编者注
对于向较早版本的兼容，从时间前后的角度来说，应叫做“向前兼容”，而从新旧前后的角度来说，应叫做“向后兼容”。本参考结合原文以及一般习惯，采用后者。因此，凡在本参考中出现“向后兼容”，均指向较早（或旧、老）的版本兼容。