Re^6: [OT] The interesting problem of comparing bit-strings.

[BrowserUk]

You spend far too much time making knee-jerk reactions to my posts,

I did not "knee-jerk". I read it and despaired for your sanity.

on the assumption that I don’t know what I am about

You don't!. You've proved that beyond a shadow of a doubt; over and over; and you're about to do it again.

and am speaking to hear my head rattle.

That's as good an explanation for it as any I suppose.

Now, step back and read my post again, starting with SCASD. You do not approach this thing “byte-wise.” Instead, you search through 64 bits at a time ... a quadword, I believe it is called.

Now you step back an read what I replied: "You cannot search for bits using byte(nor word, nor double-word)-wise instructions unless your happy to miss 75%(87%,94%) of possible hits."

Instead, you search through 64 bits at a time ... a quadword, I believe it is called.

SCASD is a Double word --ie. 32-bits -- you twonk!

(You just read my use of the term throughout this thread; and now your regurgitating your screen-reflected knowledge back at me? You utter twonk!)

There is a quadword version, but it's not x86 as you suggested above, but x64; and its a SCAS instruction no suffix, and requires a REX.W prefix; all of which will go completely over your rattling head.

But even that is completely useless for a bitstring search -- even more useless than SCASB/W/D.

Because it would require that you make 64 complete passes of the entire (1/4GB) haystack to detect that what you are looking for doesn't exist; and upto 63 complete passes to find it, even if it was right there at the very beginning. Everything you said in the first post was wrong; and with this rehashed, regurgitated, reiteration, it continues to be wrong! You total and utter twonk!

For an explanation (that you won't understand), read: Re^6: [OT] The interesting problem of comparing bit-strings. & Re^8: [OT] The interesting problem of comparing bit-strings..

You cannot do efficient bit-string searches using byte/word/double word or quadword string-scan instructions. Full stop. Now please STFU.