Anubha Agarwal wrote and asked for a video covering Search String (SRST). I don’t have a video quite yet, but here are my notes on this instruction. It’s an interesting one that can be used to search for the first occurrence of a single character in a given area of storage. It was probably added to the instruction set to help compiler writers who needed to search for C strings which are terminated with X’00’.
The interesting feature of the instruction is that it can be interrupted by the CPU for efficiency reasons when searching large areas of storage. The programmer can then decide whether to continue searching or not.
I stumbled over the examples given in the Principles of Operation, until I realized the code is flawed. A BC 1,LOOP instruction should be BC 3,LOOP, so pay close attention to those two examples.
Now that I’ve written down my thoughts, I’ll put together a video soon and provide some program examples you can experiment with. This instruction is definitely worth a look.
I’ve been working on a new assembler book for a while – writing new material and organizing the old material I’ve written into a coherent whole. I think there is a need for a book aimed at beginning assembler programmers, and this is my best attempt. I love John Erhman’s assembler text, Assembler Language Programming for IBM z System Servers – Version 2.00. It’s hard to beat John’s book for the wealth of material it contains. But I would characterize that book as a reference book, rather than a textbook. What I’m aiming for is a text that an instructor could use for a class, or a book that an interested reader could use on their own to learn IBM assembly language. So the book introduces topics in an order I found helpful for teaching beginners. I hope that together these two books will help you master this language.
Here is where you come in: I could use your help. I’m publishing each of the completed chapters on the website for you to use. If you find errors or have suggestions for making it better, let me know. You see, I’m not punctilious. I try to be – it’s a goal – but I’m not, and I need your help finding errors. At some point, I’ll put all the chapters together into a physical book and make it available to you. In the meantime, help me make this better now.
I’ll be teaching a beginning assembler class online again this fall through the Marist College IDCP as part of a two-course sequence. Together, we will write a series of assembler programs that lead to the mastery of skills needed to write assembler programs professionally. Each year, I add new materials and lectures to the course. Class sizes are manageably small, and I’ll communicate with you through on-line office hours and by email. Access to an IBM mainframe is provided as part of the course. Successful completion of these courses leads to IBM Digital certification. You can read more about the IDCP program here. Enrollment is going on now. Contact Roberta Diggins for more information (email: email@example.com or phone: 845-575-3601).
The IDCP offers courses in four areas: 1) Z/OS Programming and Applications, 2) Data Center, 3) Cybersecurity, and 4) Emerging Technologies, including an Introduction to Quantum Computing Algorithms and Programming.
I hope to see you in the fall.
Some programs run so often we take special efforts to make sure that only one copy of the program needs to be loaded into memory, no matter how many users are running it concurrently. That’s what reentrant programming is all about. We can do this by dynamically allocating storage for all the parts of our program that might change. Each user gets their own copy of dynamic storage.
Want to get your assembler program to run in the Language Environment? It needs to be reentrant. Future posts will cover COBOL calling Assembler and Assembler calling COBOL in the Language Environment, but to follow along, you first have to learn how to write assembler reentrantly.
Some programmers write all their programs in a reentrant style. There’s not a lot of extra overhead. Want to give it a try? I’ve posted a video about how it works here and in the assembler video course. There’s also a sample reentrant program you can start with here. The video explains in detail how the program works.
It can be fun to take a look at the assembly language listing of a Cobol program. Geeky, admittedly, but still fun. If you have never given the listings much thought, take a look at this video. You might be surprised what the Cobol compiler gets up to, and what you can learn about Cobol and assembler. In this video I examine whether to COMPUTE or not to COMPUTE, whether to PERFORM or to PERFORM THRU, and what happens when you tell the optimizer to give it the old college try.
If you are looking to improve your enterprise System Z computing skills including Networking, Security, COBOL, Assembler, DB2 and IMS, check out the Institute for Data Center Professionals that is sponsored by Marist College in Poughkeepsie, NY. They have an excellent System Z online program that is designed for anyone trying to advance their technical skills. The curriculum is extensive and unique. I taught a couple of assembler courses in the program last year. The program is very hands-on and you receive lots of personal assistance. If you are interested in this year’s program, you will need to hurry, though. Classes start in September. Here’s the link: http://idcp.marist.edu/
MVO is an old instruction that has fallen out of use, replaced by SRP. Still, you will see it in older programs. This video will get you up to speed on this “odd” instruction. You will also find the code from the video here.