Matlab 中整数列表的汉明权重

发布于 2025-01-08 09:55:55 字数 204 浏览 2 评论 0原文

一个非常简单的问题：我有一个整数列表，例如，

 a = [7 8]

现在我想要一个单独的列表，其中包含汉明权重（即列表中每个整数的二进制表示形式中 1 的位数。这意味着上面整数列表的结果应如下所示：

 res = [3 1]

有人知道如何快速完成此操作吗？

原文

Quite a simple problem: I have a list of integers, e.g.,

 a = [7 8]

Now I want to have a seperate list, that contains the Hamming Weight (that is the
number of 1 bits in the binary represenation) for each of the integers in the list. That means the result for the integer list above should look as follows:

 res = [3 1]

Anyone an idea how I could do this quickly?

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一江春梦 2025-01-15 09:55:55

这有点 hacky，但它有效：

res = sum( dec2bin(a).' == '1' );

它将 a 转换为二进制表示形式，查看该表示形式中有多少个字符是 '1'，并对这些数字求和。

This is a little hacky, but it works:

res = sum( dec2bin(a).' == '1' );

It converts a to binary representation, looks at how many characters in that representation are '1', and sums up those numbers.

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趁微风不噪 2025-01-15 09:55:55

#% Quickly for a few or quickly for millions?
#% A quick method for a 32 bit int requires a 16 bit look-up table
#% Ideally the table is created once and passed to the function for usage
#% vectorized
vt=randi(2^32,[4096*4096,1])-1; #% input vector vt

num_ones=uint8(zeros(65536,1));
for i=0:65535
 num_ones(i+1)=length( find( bitget( i, 1:32 ) ) ) ;
end % 0.43 sec to create table

v=num_ones(mod(vt,65536)+1)+num_ones(floor(vt/65536)+1); #% 0.85 sec
% dec2bin is 1000 times slower

#% Quickly for a few or quickly for millions?
#% A quick method for a 32 bit int requires a 16 bit look-up table
#% Ideally the table is created once and passed to the function for usage
#% vectorized
vt=randi(2^32,[4096*4096,1])-1; #% input vector vt

num_ones=uint8(zeros(65536,1));
for i=0:65535
 num_ones(i+1)=length( find( bitget( i, 1:32 ) ) ) ;
end % 0.43 sec to create table

v=num_ones(mod(vt,65536)+1)+num_ones(floor(vt/65536)+1); #% 0.85 sec
% dec2bin is 1000 times slower

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