Talk:Barrel shifter

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This article is based on material taken from the Free On-line Dictionary of Computing prior to 1 November 2008 and incorporated under the "relicensing" terms of the GFDL, version 1.3 or later.

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[reply]

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)[reply]

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)[reply]

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)[reply]

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 “barrel and slot”.) 50.181.30.121 (talk) 01:54, 13 April 2014 (UTC)[reply]

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)[reply]

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)[reply]