Python是用C编写的,实际上是C程序,这使我想知道如何处理小数点赋值。
C程序如何实现非常大的十进制数(大于int或long)的Python变量赋值?
例如:
a=10000... # a=(10^1000)
当在python中运行时,我知道该值太大,以至于它需要占用内存中的许多单词,因此C程序显然可以做到这一点,但是如何呢?
C中的每个变量都有一个类型,但是C编译后的代码不知道数字将是多少。
(python)C程序如何处理该分配? (以及对此类变量的操作)
最佳答案
这是CPython 2.7.5中用来表示长整数的C struct
:
/* Long integer representation.
The absolute value of a number is equal to
SUM(for i=0 through abs(ob_size)-1) ob_digit[i] * 2**(SHIFT*i)
Negative numbers are represented with ob_size < 0;
zero is represented by ob_size == 0.
In a normalized number, ob_digit[abs(ob_size)-1] (the most significant
digit) is never zero. Also, in all cases, for all valid i,
0 <= ob_digit[i] <= MASK.
The allocation function takes care of allocating extra memory
so that ob_digit[0] ... ob_digit[abs(ob_size)-1] are actually available.
CAUTION: Generic code manipulating subtypes of PyVarObject has to
aware that longs abuse ob_size's sign bit.
*/
struct _longobject {
PyObject_VAR_HEAD
digit ob_digit[1];
};
如果您想进一步探索,请访问download the source code并查看以下文件:
./Include/longintrepr.h
./Include/longobject.h
./Objects/longobject.c
这将告诉您您可能希望知道的每一个细节。 :)