为什么python的内置乘法如此快

问题描述

所以，有一天我在python中尝试一些东西，我试图在python中编写自定义乘法函数

  def multi（x，y）：
z = 0 
而y> 0：
z = z + x 
y = y-1 
返回z 
  

但是，当我以极大的数字运行它时，例如（1 因此，我尝试研究了不同类型的乘法，例如在那里实施的俄罗斯农民乘法技术，该方法非常快，但不如multi（x，y）可读。

  def Russian_peasant（x，y）：
z = 0 
而y> 0：如果y％2 == 1，则
：z = z + x 
 x = x< 1 
 y = y>> 1 
 return z 
  

我想让您回答的是python之类的编程语言如何乘法数字？

解决方案

您的 multi 版本以O（N）运行，而 russian_peasant 版本以O（logN）运行，比O（N）更好。

了解您的速度有多快 russian_peasant 版本是，请检查此

 来自数学导入日志
 print round（log（100000000，2））＃27.0 
  

因此，循环必须是仅执行了27次，但是当 y 为100000000时，您的 multi 版本的while循环必须执行100000000次。 / p>

要回答其他问题，

Python使用，但用于。

基本乘法是用C代码处理的，可以编译为机器代码并更快地执行。

So the other day I was trying something in python, I was trying to write a custom multiplication function in python

def multi(x, y):
    z = 0
    while y > 0:
        z = z + x
        y = y - 1
    return z

However, when I ran it with extremely large numbers like (1 << 90) and (1 << 45) which is (2 ^ 90) * (2 ^ 45). It took forever to compute.So I tried looking into different types of multiplication, like the russian peasant multiplication technique, implemented down there, which was extremely fast but not as readable as multi(x, y)

def russian_peasant(x, y):
    z = 0
    while y > 0:
        if y % 2 == 1: z = z + x
        x = x << 1
        y = y >> 1
    return z

What I want you to answer is how do programming languages like python multiply numbers ?

解决方案

Your multi version runs in O(N) whereas russian_peasant version runs in O(logN), which is far better than O(N).

To realize how fast your russian_peasant version is, check this out

from math import log
print round(log(100000000, 2))   # 27.0

So, the loop has to be executed just 27 times, but your multi version's while loop has to be executed 100000000 times, when y is 100000000.

To answer your other question,

Python uses O(N^2) grade school multiplication algorithm for small numbers, but for big numbers it uses Karatsuba algorithm.

Basically multiplication is handled in C code, which can be compiled to machine code and executed faster.

这篇关于为什么python的内置乘法如此快的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！