在V8中，如何将原始类型（如null，undefined和boolean）存储在内存中？ [英] In V8, how are primitive types such as null, undefined, and boolean stored in memory?

问题描述

boolean 是否在内存中存储为32字节整数？如果 null 值？

Is a boolean stored as a 32-byte integer in memory? How about a null value?

在书中使用Javascript ，
它指的是类型标记，用于指示存储在内存中的值的类型。例如 Object 类型的类型标签是000.什么是类型标签？

In the book Speaking Javascript, it refers to a type tag being used to indicate the type of a value stored in memory. e.g. The type tag for Object type was 000. What is a type tag?

我如何找到类型标记的值类型，例如布尔或字符串？

How would I find the type tag of a value type such as a boolean or string?

推荐答案

来自Andy Wingo的关于该主题的博客文章：

From Andy Wingo's blog post on the topic:

最初，所有JavaScript实现都使用标记指针代表JS值。这是一个老技巧，来自观察到分配的内存占用至少4或8个字节，并以最低有效位或3为零的方式对齐。

Initially, all JavaScript implementations used tagged pointers to represent JS values. This is a old trick that comes from the observation that allocated memory takes up at least 4 or 8 bytes, and are aligned in such a way that the least significant bit or three will be zero.

因此类型标签允许统一存储所有值。所有值占用一个机器字（32/64位），并且根据标记（最低有效位或位），它们被解释为指向对象的指针或根据标记的某些整数/布尔/等。

So the type tags allow for all values to be stored uniformly. All values occupy one machine word (32/64 bit) and depending on the tag (which is the least significant bit or bits) they are interpreted either as a pointer to an object or as some integer/boolean/etc depending on the tag.

布尔存储为js内存中的32字节整数？

is boolean stored as a 32-byte integer in js memory?

布尔值也占用一个单词。对于更具体的答案，我需要通过v8源代码。但如果我没记错的话， true 和 false 表示为根指针。

A boolean also occupies one word. For a more specific answer I'd need to go though the v8 source. But if I remember correctly, true and false are represented as root pointers.

如何获取值类型的类型标记（boolean，undefined，string，number）;

how to get the type tag of a value type(boolean,undefined,string, number);

无法通过JavaScript实现。这是内部实施细节。

No way to do it from JavaScript. It's internal implementation details.

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