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RULES(NOEVENPACK) in cobol


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jackzhang75

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Joined: 09 Jun 2014
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PostPosted: Wed Mar 29, 2017 12:47 am
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Hello experts,

I am reading the following statment and i am not sure why we must have the pack decimal in odd digit? Is following statement is ture that you can only have odd number of digits in hardware ? Can you give me a example to show why it say that ?? Thank you very much!

Code:
RULES(NOEVENPACK) This complier option will tell you if you accidentally define a Pack Decimal data item within even number of digits. You can only have odd number of digits in hardware. If you have one byte you have one digit , 2 byte you have 3 digit, 3 byte -->5 digit.


Thanks
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Robert Sample

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PostPosted: Wed Mar 29, 2017 12:54 am
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Packed decimal variables should have an odd number of digits due to the internal representation. The value 12345 in zoned decimal is X'F1F2F3F4F5' (if unsigned). The same value in packed decimal is X'12345F'. Packed decimal variables that have an odd number of digits will fit precisely into the hexadecimal bytes.

If you have a packed decimal variable with an even number of digits, that extra digit requires an extra byte to store the value. While it is not illegal to have an even number of digits, there are extra pseudo-assembler statements generated in COBOL to account for the extra digit (and make sure the value does not exceed the PICTURE size if TRUNC(STD) is being used). It is more efficient to have the odd number of digits for a packed decimal variable (and note that this ONLY holds true for packed decimal variables).
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jackzhang75

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PostPosted: Wed Mar 29, 2017 1:27 am
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Robert, thank you very much for you answer. Could you give me an example of COBOL code to illustrate odd and even pack decimal ? I think i got the idea but still not sure what is the right code should be?
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Robert Sample

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PostPosted: Wed Mar 29, 2017 2:05 am
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I'm not really sure what you think an example is going to show you:
Code:
       05  WS-ODD           PIC S9(07) COMP-3. 
       05  WS-EVEN          PIC S9(08) COMP-3. 
You should always use an odd number of digits, like WS-ODD, and not an even number of digits like WS-EVEN.
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Bill Woodger

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PostPosted: Wed Mar 29, 2017 2:23 am
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jackzhang75,

Please don't post questions in multiple places at the same time. You posted it on StackOverflow, and just wasted either Robert's or my time. That doesn't tend to help you get answers when next you ask.
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jackzhang75

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PostPosted: Wed Mar 29, 2017 5:03 am
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Oh.. i am really sorry and i will not post it in anohter place again. Again very appreicated for your answer really help me alot!
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