ada中mod运算符的使用

发布于 2024-08-30 09:34:08 字数 162 浏览 9 评论 0原文

谁能告诉我以下声明的用法，如下所示。我是 ada 语言的初学者。我尝试过互联网，但还不够清楚。

            type Unsigned_4 is mod 2 ** 4;
            for Unsigned_4'Size use 4;

原文

Can anyone please tell me the usage of the following declarations shown below.I am a beginner in ada language.I had tried the internet but that was not clear enough.

            type Unsigned_4 is mod 2 ** 4;
            for Unsigned_4'Size use 4;

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猫烠⑼条掵仅有一顆心 2024-09-06 09:34:08

Unsigned_4 是一种“模块化类型”，取值 0、1、.. 14、15，并进行环绕。

   U : Unsigned_4;
begin
   U := Unsigned_4'Last;      -- 15
   U := U + 1;                -- 0

您只需要 4 位来实现该类型，因此可以将其指定为其大小（我认为这可能只是一个确认规范，因为编译器已经清楚地知道这一点；如果您希望将其装入 3 位并说对于 Unsigned_4'Size 使用 3； 编译器会告诉你你错了）。

大多数编译器希望将类型的值存储在至少一个字节中，以便有效访问。当您在打包记录（pragma Pack）中使用该类型时，最小大小就会发挥作用。

Unsigned_4 is a "modular type" taking the values 0, 1, .. 14, 15, and wrapping round.

   U : Unsigned_4;
begin
   U := Unsigned_4'Last;      -- 15
   U := U + 1;                -- 0

You only need 4 bits to implement the type, so it's OK to specify that as its Size (I think this may be simply a confirming spec, since the compiler clearly knows that already; if you were hoping to fit it into 3 bits and said for Unsigned_4'Size use 3; the compiler would tell you that you were wrong).

Most compilers will want to store values of the type in at least a byte, for efficient access. The minimum size comes into its own when you use the type in a packed record (pragma Pack).

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