有点抨击 [英] bit bashing
问题描述
这是一小块程序（再次只有14行程序）
计算一个数字中设置的位数。
输入
输出
0
0（0000000）
5
2（0000101）
7
3（0000111）
int CountBits（unsigned int x）
{
static unsigned int mask [] = {0x55555555，
0x33333333，
0x0F0F0F0F，
0x00FF00FF，
0x0000FFFF
};
int i;
int shift; / *要转移到右边的位置数* /
for（i = 0，shift = 1; i< 5; i ++，shift * = 2）
x =（x& mask [i]）+（（x> shift）& mask [i]）;
返回x;
}
找出上述程序中使用的逻辑。
< blockquote> Rohit kumar Chandel写道：
做你自己的作业，或者给我们你的
老师的地址。我们会直接给他回答
-
jacob navia
jacob at jacob point remcomp point fr
logiciels / informatique
http：// www。 cs.virginia.edu/~lcc-win32
Rohit kumar Chandel写道：
这是一小块程序（再次只有14行程序）
....
找出上述程序中使用的逻辑。
这对我来说闻起来像家庭作业......我还没有做过30多年的家庭作业 - 我为什么要做你的作业？
" jacob navia" < ja *** @ nospam.com写信息
新闻：fn ********** @ aioe.org ...
Rohit kumar Chandel写道：
做你自己的作业，或者给我们你的
老师的地址。我们会直接向他发送答案
这不是一个家庭作业问题。我试图理解逻辑，但是
无法得到它。
这是一段代码，从我的朋友那里传来作为一个谜题。我
一般计算这样设置的位数：
int CountBits（unsigned int x）
{
int count = 0;
while（x）
{
count ++;
x = x& ;（x-1）;
}
返回计数;
}
更简单。
现在我可以得到一个答案，或者你还需要我老师的地址:-)
问候
Rohit
Here is a small piece of program(again just 14 lines of program) which
counts the number of bits set in a number.
Input
Output
0
0(0000000)
5
2(0000101)
7
3(0000111)
int CountBits (unsigned int x )
{
static unsigned int mask[] = { 0x55555555,
0x33333333,
0x0F0F0F0F,
0x00FF00FF,
0x0000FFFF
} ;
int i ;
int shift ; /* Number of positions to shift to right*/
for ( i =0, shift =1; i < 5; i ++, shift *= 2)
x = (x & mask[i ])+ ( ( x >shift) & mask[i]);
return x;
}
Find out the logic used in the above program.
Rohit kumar Chandel wrote:
Do your own homework, or give us the address of your
teacher. We will send him the answer directly
--
jacob navia
jacob at jacob point remcomp point fr
logiciels/informatique
http://www.cs.virginia.edu/~lcc-win32
Rohit kumar Chandel wrote:Here is a small piece of program(again just 14 lines of program)....
Find out the logic used in the above program.This smells like homework to me... I haven''t done homework in over 30
years - why should I do yours?
"jacob navia" <ja***@nospam.comwrote in message
news:fn**********@aioe.org...Rohit kumar Chandel wrote:
Do your own homework, or give us the address of your
teacher. We will send him the answer directly
This is not a homework question. I have tried to understand the logic but
could not get it.
This is a piece of code which came to me from my friend as a puzzle. I
generally calculate number of bits set like this:
int CountBits(unsigned int x)
{
int count=0;
while(x)
{
count++;
x = x&(x-1);
}
return count;
}
which is much simpler.
Now can I get an answer, or still you need address for my teacher :-)
Regards
Rohit
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