Python 是用 C 编写的并且实际上是一个 C 程序这一事实让我想知道如何处理十进制数赋值。
C程序如何实现一个非常大的十进制数(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,我知道这个值太大以至于它在内存中占用了很多单词,所以 C 程序显然是这样做的,但是如何呢?
C 中的每个变量都有一个类型,但 C 编译代码不知道这个数字有多大。
(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 中用来表示长整型的 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,download the source code并查看以下文件:
./Include/longintrepr.h
./Include/longobject.h
./Objects/longobject.c
这会告诉您您可能希望知道的每一个细节。 :)
关于python - C如何实现大数的Python赋值,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19381492/