计数被设置的比特数 [英] Counting the number of bits that are set

问题描述

欲计数被设置一个二进制数位的数量。
例如，用户输入是二进制01100001数97。该计划应该给我的3位被使用MIPS ISA设置。

I want to count the number of bits in a binary number that are set. For example, user enter the number 97 which is 01100001 in binary. The program should give me that 3 bits are set using MIPS ISA.

我能够用C来实现这一点，但我不知道如何使用汇编code来实现它。

I am able to achieve this in C, but I don't know how to achieve it using assembly code.

任何想法？

在此先感谢所有帮助。

Thanks in advance for all the help.

这是不是硬件，它的我的研究项目的一小部分。

This is not HW, its a tiny part of my research project.

推荐答案

什么你要找的是通常被称为人口数（popcount）。

What you're looking for is often referred to as the population count (popcount).

有一些在位操作黑客 C实现的（一些这些都是scarily聪明）。如果你熟悉C，每种方法应该有一个合理的翻译成MIPS汇编打破前任pressions后。

There are a number of C implementations on Bit Twiddling Hacks (some of which are scarily clever). If you're familiar with C, each approach should have a reasonable translation into MIPS assembly after breaking down the expressions.

如果您输入的域名是小（例如0-255），你总是可以做一个查找表和使用输入作为偏移，直接获取popcount。

If your input domain is small (e.g. 0-255), you could always do a lookup table and use the input as the offset to fetch the popcount directly.

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