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‎BasicObject/float/float.md‎

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* [0.1](#0.1)
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* [1.1](#1.1)
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* [-0.1](#-0.1)
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* [summary](#summary)
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* [free_list](#free_list)
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#### related file
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* cpython/Objects/floatobject.c
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##### 0
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the binary representation of 0.0 in **IEEE 754** format is all bit in zero
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the binary representation of 0.0 in **IEEE 754** format is 64 zero bits
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f = 0.0
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![-0.1](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/-0.1.png)
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##### nonascii characters
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##### free_list
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s = "我是帅哥".encode("utf8")
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#ifndef PyFloat_MAXFREELIST
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#define PyFloat_MAXFREELIST 100
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#endif
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static int numfree = 0;
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static PyFloatObject *free_list = NULL;
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free_list is a single linked list, store at most PyFloat_MAXFREELIST **PyFloatObject**
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![free_list](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/free_list.png)
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The linked list in linked via the field **ob_type**
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>>> f = 0.0
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>>> id(f)
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4551393664
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>>> f2 = 1.0
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>>> id(f2)
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4551393616
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del f
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del f2
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![free_list2](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/free_list2.png)
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**f3** comes from the head of the **free_list**
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>>> f3 = 3.0
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>>> id(f3)
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4551393616
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![free_list3](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/free_list3.png)

‎BasicObject/float/float_cn.md‎

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# float
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### 目录
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* [相关位置文件](#相关位置文件)
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* [内存构造](#内存构造)
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* [示例](#示例)
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* [0](#0)
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* [1](#1)
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* [0.1](#0.1)
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* [1.1](#1.1)
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* [-0.1](#-0.1)
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* [free_list](#free_list)
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#### 相关位置文件
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* cpython/Objects/floatobject.c
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* cpython/Include/floatobject.h
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* cpython/Objects/clinic/floatobject.c.h
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#### 内存构造
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**PyFloatObject** 仅仅是一层对 c 语言中双精度浮点数的包装(**double**), 一个双精度浮点数使用8个字节去表示一个浮点数
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详细的内容可以参考 [IEEE 754](https://en.wikipedia.org/wiki/IEEE_754-1985)/[IEEE-754标准与浮点数运算](https://blog.csdn.net/m0_37972557/article/details/84594879)
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![layout](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/layout.png)
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#### 示例
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##### 0
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0.0 使用 **IEEE 754** 标准的表示方式为 64 个为 0 的 bit
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f = 0.0
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![0](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/0.png)
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##### 1.0
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f = 1.0
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![1](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/1.png)
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##### 0.1
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f = 0.1
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![0.1](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/0.1.png)
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##### 1.1
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1.1 和 0.1 的区别是指数位最后的几个位不相同
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![1.1](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/1.1.png)
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##### -0.1
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-0.1 和 0.1 的区别是第一个符号位不相同
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![-0.1](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/-0.1.png)
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##### free_list
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#ifndef PyFloat_MAXFREELIST
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#define PyFloat_MAXFREELIST 100
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#endif
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static int numfree = 0;
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static PyFloatObject *free_list = NULL;
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free_list 是一个单链表, 最多存储 **PyFloat_MAXFREELIST** 个 **PyFloatObject**
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![free_list](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/free_list.png)
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单链表通过 **ob_type** 字段串联起来
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>>> f = 0.0
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>>> id(f)
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4551393664
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>>> f2 = 1.0
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>>> id(f2)
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del f
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del f2
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![free_list2](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/free_list2.png)
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**f3** 取自 **free_list** 的表头
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>>> f3 = 3.0
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>>> id(f3)
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4551393616
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![free_list3](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/free_list3.png)

‎BasicObject/float/free_list.png‎

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‎BasicObject/float/free_list2.png‎

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‎BasicObject/float/free_list3.png‎

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‎README.md‎

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- [x] [long/int](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/long/long.md)
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- [x] [bytes](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/bytes/bytes.md)
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- [x] [bytearray](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/bytearray/bytearray.md)
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- [ ] [float](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/float.md)
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- [x] [float](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/float.md)
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- [ ] func
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- [ ] method
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- [ ] iter

‎README_CN.md‎

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- [x] [long/int](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/long/long_cn.md)
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- [x] [bytes](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/bytes/bytes_cn.md)
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- [x] [bytearray](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/bytearray/bytearray_cn.md)
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- [ ] [float](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/float_cn.md)
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- [x] [float](https://github.com/zpoint/Cpython-Internals/blob/master/BasicObject/float/float_cn.md)
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- [ ] func
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- [ ] method
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- [ ] iter

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