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niks_jude
Joined: 01 Dec 2006
Posts: 81
Location: Mumbai
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| Posted: Mon Jul 21, 2008 12:40 pm Post subject: NI Instruction on LABEL? |
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Can anybody explain the result of this instruction -
NI NOSEP+1,X'0F'
Where NOSEP is a label
NOSEP B SKIP1
LA R8,2
ALIGN1 CLI HALIGN,X'FF'
BER R7 |
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enrico-sorichetti
Joined: 14 Mar 2007
Posts: 3082
Location: italy
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| Posted: Mon Jul 21, 2008 1:30 pm Post subject: Reply to: NI Instruction on LABEL? |
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it turns a branch into a noop
the branch instruction should be x'47xrbddd'
Code:
47 - opcode
x - condition code
r - index register
b - base register
ddd - offset
doing a x'0f' ni on the second byte will turn the x to a 0
usually is a trick ( now frowned upon ) to take a branch the first time and the fall thru the other times |
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niks_jude
Joined: 01 Dec 2006
Posts: 81
Location: Mumbai
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| Posted: Mon Jul 21, 2008 1:33 pm Post subject: |
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| That helps.Thanks. |
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niks_jude
Joined: 01 Dec 2006
Posts: 81
Location: Mumbai
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| Posted: Mon Jul 21, 2008 2:28 pm Post subject: |
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Oh I got a little confused, please help-
B EXITLP1
EXITLP2 NI MATCH00X+1,0 (this will branch or not and to which subroutine)
BR R7 |
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enrico-sorichetti
Joined: 14 Mar 2007
Posts: 3082
Location: italy
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| Posted: Mon Jul 21, 2008 2:37 pm Post subject: Reply to: NI Instruction on LABEL? |
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MATCH00X is the branch instruction being modified
if You do not post it we cannot tell
please use the code tag, it will make coding more readable |
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niks_jude
Joined: 01 Dec 2006
Posts: 81
Location: Mumbai
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| Posted: Mon Jul 21, 2008 3:22 pm Post subject: |
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These are the two labels/subroutines -
Code: MATCH00X B PWRRETN
PWRRETN L R7,SV7A
BR R7 RETURN |
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enrico-sorichetti
Joined: 14 Mar 2007
Posts: 3082
Location: italy
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| Posted: Mon Jul 21, 2008 3:31 pm Post subject: Reply to: NI Instruction on LABEL? |
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the logic is the same as before,
the first time the branch will be taken, the second time not...
if You have problems understanding the program flow
it would be wiser to ask Your peers ( application developers ) about it or try to get the original program specificatons |
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Bill O'Boyle
Joined: 14 Jan 2008
Posts: 333
Location: Orlando, FL, USA
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| Posted: Mon Jul 21, 2008 3:38 pm Post subject: Re: Post subject: NI Instruction on LABEL? |
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This could open a can of worms if this code is in CICS.
In my previous life, I had to maintain code that altered instructions, without using an EX, such as inserting a length into a subsequent MVC via an STC *+5.
Don't do this....
Regards,
Bill |
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