Talk:Barrel shifter

Why "barrel"
Where does the word "barrel" come from in the name or what does it mean?

As in the barrel of a gun. When it rotates, it takes all of the bits a particular distance at once.

This is in contrast to earlier register-based single shifting mechanisms based on chains of flip flops.

193.35.132.19 (talk) 21:36, 22 February 2011 (UTC)REH2

Except the barrel of a gun doesn't rotate. In revolvers it's the cylinder that does that.

I note that storage barrels are often moved by rolling them (as in the song "Roll out the Barrel").

Cost
The calculation is incorrect: It should be simply log2 n. This assumes (for simplicity) that each of the multiplexers are n bits wide. The first stage shift's across 1 bit line, the next 2 lines, 4, 8, and so on. An interesting side-effect of this arrangement is that the shift number is specified directly in binary notation, without the need for a decoder of any sort. — Preceding unsigned comment added by REH2 (talk • contribs) 14:52, 23 February 2011 (UTC)

diagram
like at http://www-comm.cs.shinshu-u.ac.jp/public/comparch/node45.html or http://www.realworldtech.com/page.cfm?ArticleID=RWT081502231107&p=3 `a5b (talk) 21:17, 5 July 2011 (UTC)
 * here www.lirmm.fr/arith18/papers/hilewitz-PerformingBitManipulations.pdf at page 9 are pictured two types of barell shifters: classic one and log shifter. `a5b (talk) 21:35, 5 July 2011 (UTC)

Inventor
Is there any consensus on the inventor of the barrel-style shifter, or on the first processor to implement it? I recall that Seymour Cray used one in the CDC 6600 ca. 1963-4. Some casual Internet searching suggests that Burroughs may also have a claim, possibly with its B5000. (Note that I'm not talking about the CDC 6600's I/O system, which has been described using the similar-but-unrelated term &ldquo;barrel and slot&rdquo;.) 50.181.30.121 (talk) 01:54, 13 April 2014 (UTC)

Diagram does not match text
Diagram shows 4-bit barrel shifter with 16 multiplixers. Cost section says number of multiplexers required for 4 bits is 4*log2(4) = 4*2 = 8. 8 is not 16. Which of these is incorrect: The diagram, or the cost section? If neither, then what additional information is missing from this article? --24.47.169.50 (talk) 16:39, 26 April 2015 (UTC)

Bit Rotation vs. Bit Shifting
"and thus make any cyclic combination of A, B, C and D" yes that's called bit rotation that is some amazing newf@g f@ggotry right there — Preceding unsigned comment added by 195.168.40.226 (talk) 08:22, 12 August 2016 (UTC)