A charlatan makes obscure what is clear; a thinker makes clear what is obscure.
I am doing a startup!
Cross-browser testing from your browser!
I have written my fourth book!
Be faster than Larry Wall in the shell!
You're viewing a comment by John Doe and its responses.
I was not questioning the need for resetting the LSB. There are countless examples for that.
What I WAS saying, however, is that the expression you stated, y = x & (x-1), IS WRONG.
You may have proofread your article, but this is still a mistake. And though I have already shown you two examples in my first post, I will do that again, just so everything's clear:
Let X be 0101010b / 02Ah / 42d.
Let y = x & (x-1):
(0101010 & 0101001) / (02Ah & 029h)
y equals 0101000 / 028h.
Not only was the LSB reset,
but the bit at n=1 as well.
Let X be 10b / 02h / 2d.
Let y = x & (x-1):
(10 & 01) / (02h & 01h)
y equals 00.
The general example, as I already stated in my first post, is that any number ending with the last two bits 10 invalidates the claim, since the result of the expression is that BOTH the last two bits are reset.
As you know, it is sufficient to produce one contradictory example in order to invalidate any rule.
Have a nice day.
First to be clear, Peter' claim was to clear the right-most 1 bit, not to be confused with clearing the LSB: (e.g. 0xABCD & 0xFFFE).
So in both of your examples, which you use binary numbers ending in 10b, the result is that the right-most 1 bit (e.g. the n-1 position) is indeed cleared resulting in 00b.
So what's the problem? The original number x ending in 10b already had 0 as its LSB before the operation and post operation it's still 0. The only thing that changes was the right most 1 bit which was in the n-1 position.
This is not a counter-example. Rather, you've just given more examples to support the operation.
(why do I need your e-mail?)
It would be nice if you left your e-mail address. Sometimes I want to send a private message, or just thank for the great comment. Having your e-mail really helps.
I will never ever spam you.
(Your twitter handle, if you have one.)
* use <pre>...</pre> to insert a plain code snippet.
* use <pre lang="lang">...</pre> to insert a syntax highlighted code snippet.
For example, <pre lang="python">...</pre> will insert Python highlighted code.
* use <code>...</code> to highlight a variable or a single shell command.
* use <a href="url" nospam>title</a> to insert links.
<a href="url" nospam>title</a>
* use other HTML tags, such as, <b>, <i>, <blockquote>, <sup>, <sub> for text formatting.
Type the word "unix_143": (just to make sure you're a human)
Please preview the comment before submitting to make sure it's OK.
Peter Krumins' blog about programming, hacking, software reuse, software ideas, computer security, browserling, google and technology.
Reach me at:
Or meet me on:
Subscribe through an RSS feed:
Subscribe through email:
Enter your email address:
Delivered by FeedBurner
See all top articles
See all downloads
See more detailed list of recent articles
See more detailed category information
See more detailed list of all articles