SRST will do it nicely.  From the instruction samples in Appendix A of the PoOP:

SRST Example 2
Following is an example program that determines the
address of the first character equal to C1 hex in the
string A whose length is known. The program is not
written for execution in the access-register mode.
     L 5,STRAADR
     L 4,STRALEN
     AR 4,5
     LA 0,X'C1'
LOOP1 SRST 4,5
     BC 1,LOOP1     <== IMHO use BRC for both of these, but this is what IBM 
gave us
     BC 2,NOTFND
FOUND [Any instruction]
...
NOTFND [Any instruction]

In this example, the value in STRALEN may be a
length that either does or does not include an ending
character at the end of the string, provided that the
ending character is not the character for which the
search is made.

HTH

Peter

-----Original Message-----
From: IBM Mainframe Discussion List [mailto:[email protected]] On Behalf 
Of Pinnacle
Sent: Friday, March 13, 2015 1:28 PM
To: [email protected]
Subject: Need assembler trick to quickly get second and third DS qualifiers

I have a dataset FIRST.SECOND.THIRD, and I want to get SECOND.THIRD.  
Normally I would loop to one character at a time to get to the '.', but 
I need performance here.  I sure some of you assembler gurus could give 
me some inscrutable assembler to get there in like one or two 
instructions.  Thanks in advance!

Regards,
Tom Conley

-- 
  


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