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Preety
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Joined: 15 Mar 2005
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 Posted: Mon Apr 30, 2007 3:08 pm Post subject: Shift operation in Assembler |
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Hello,
As Logical left shift operation on binary numbers performs multiplication by 2 , what is the significance of performing Circular shift(both right circular shift and Left circular shift ) in Assembly Language?
Thanks.
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Bill Dennis
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| Posted: Mon Apr 30, 2007 3:35 pm Post subject: |
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Possibly to "round" the number to some multiple of 2 (when you shift back left zeroes are inserted)?
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Bill Dennis
Disclaimer: My comments on this foorum are my own and do not represent the opinions or suggestions of any other person or business entity. |
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CICS Guy
Intermediate
Joined: 30 Apr 2007
Posts: 292
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| Posted: Tue May 01, 2007 6:08 am Post subject: Re: Shift operation in Assembler |
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| Preety wrote: | | Circular shift(both right circular shift and Left circular shift ) in Assembly Language |
What is a "circular shift"? |
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Nic Clouston
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| Posted: Tue May 01, 2007 7:10 am Post subject: |
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CICS Guy - use Google
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Utility and Program control cards are NOT, repeat NOT, JCL. |
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CICS Guy
Intermediate
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| Posted: Tue May 01, 2007 8:33 am Post subject: |
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Maybe I should have been a little more direct.
How does one perform a circular shift in assembly language? Is there an opcode for this?
From the way Preety put it, it sort of sounds like there is one...... |
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Nic Clouston
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| Posted: Tue May 01, 2007 9:20 am Post subject: |
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still available in Google - but whether it applies to mainframe or intel I could not tell
but there maybe another document - I've only looked at the first 3 (search on 'circular shift assembler')
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Utility and Program control cards are NOT, repeat NOT, JCL. |
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kolusu
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CICS Guy
Intermediate
Joined: 30 Apr 2007
Posts: 292
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| Posted: Tue May 01, 2007 10:00 am Post subject: |
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| I understood that was meant just by the "circular shift" title, I was just wondering about Preety's usage in assembler........ |
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DaveyC
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Joined: 02 Dec 2002
Posts: 151
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Location: Perth, Western Australia
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| Posted: Tue May 01, 2007 10:18 pm Post subject: |
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| CICS Guy wrote: |
How does one perform a circular shift in assembly language? Is there an opcode for this?
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RLL (Rotate Left Single Logical)
or you can store a word with the STRV (Store Reversed).
These instructions are useful for a variety of problems. For example, changing the endianess of data received from a disparate machine.
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Dave Crayford |
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Preety
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Joined: 15 Mar 2005
Posts: 23
Topics: 12
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| Posted: Wed May 02, 2007 2:57 am Post subject: |
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DaveyC,
Could you please explain the usefulness of shift operations in detail.
Thanks,
Preety |
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CICS Guy
Intermediate
Joined: 30 Apr 2007
Posts: 292
Topics: 3
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| Posted: Wed May 02, 2007 6:32 am Post subject: |
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| DaveyC wrote: | RLL (Rotate Left Single Logical)
or you can store a word with the STRV (Store Reversed). |
Neat, I just downloaded the latest PoP, over 1200 pages compared to my dog-eared 175 pager.... Boy, do I have some catching up to do..... At least I'll have some interesting bedtime reading for a while....grin..... |
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DaveyC
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Joined: 02 Dec 2002
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Location: Perth, Western Australia
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| Posted: Wed May 02, 2007 7:28 am Post subject: |
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| Preety wrote: | DaveyC,
Could you please explain the usefulness of shift operations in detail.
Thanks,
Preety |
There are far too many uses for using shifts to list them all. Some of the most common are fast multiplication by powers of two, hashing algorithms, setting-clearing- toggling bits in bitmaps etc, etc.
Not assembler, but here is a debugging function I wrote in C to convert a flag byte to a binary string of 1s and 0s. Kudos points for anybody who can tell me how it works.
| Code: |
char* c2b(
char* buffer,
unsigned char c
)
{
int i;
int numBits = CHAR_BIT;
for ( i = 0; numBits--; i++ ) {
buffer[i] = ( c & 0x80 ) ? '1' : '0';
c <<= 1;
}
buffer[i] = '\0';
return buffer;
}
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