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Old 03-17-2005, 09:25 AM   #1
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Assembly language: Purpose of shift register?

Could someone explain what the purpose of this is? It's for SPARC processor assembly language.
Old 03-17-2005, 10:56 AM   #2
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Do you mean some insttruction to shift all bits of byte to left or right?
Like "a << 4" in C?

This can be handy for:
  • Serialization of bits.
  • Binary representation, like printing the zeroes and ones.
  • Multiplication: shifting bits one position to the left is a very fast way to multiply by 2.
    Likewise, shifting to the right is dividing by 2, 4, 8, 16, 32... (resp 1,2,3,4,5,... positions).
Old 03-17-2005, 10:59 AM   #3
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No, not the shift instruction but the shift register, although it might be used for shifting bits.. hmm.

Old 03-21-2005, 05:06 PM   #4
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I think this is a bit like asking what is the purpose of the AND function.
A shift register is an easily implemented hardware block in electronics and has multiple uses when used with supplementary hardware (e.g. shift registers are often used in pseudo-random number generators to generate long sequences.)
When looking at the shift register from a higher level language viewpoint it may seem a bit pointless, but at a low level it allows you to move bits around very effectively, and in assembler that is literally what you are doing, manipulating bits directly
This looked to be a useful site on assembly language
Look-up the section on 'Shift and rotate'. It gives examples of different variations of shift register instructions that generate different end results, for manipulating bits using a shift register.
I don't know a lot about assembly, but if all these instructions are available that use shift registers in different ways, I am sure that they weren't created just for fun!
Perhaps you would have better insight if you tried to create a simple programme for a less complicated processor (such as a microcontroller.) You may find that as you try to reliase the programme that the shift register becomes very useful!!
Good luck!
Old 03-21-2005, 08:24 PM   #5
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as the above poster stated, these are for low level programming.

They make math functions extremely fast and simple. (adders and such contain these)

like hko stated, it is almost imposslbe to do low level multiplying and dividing without these while being efficient.

If you are writing math functions in assembly you will use these.


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