bobguo wrote:... i know how to use BXLE, but i would like to catch what's mean, can somebody explain these three lines? Thx.
If you know how to use BXLE - which I doubt - and you understand the previous example, you should have no trouble with this example. Try changing the second line to
Get out your "Principles of Operation" and work through the 4 times the BXLE instruction will execute. Remember that the * in the BXLE is the current location, so the first 3 times the instruction executes it will "branch" to itself. Remember the formal name of the instruction is "branch on index low or equal." Change the word "index" to "value," or in the earlier example, "address," and you will have it.
I sort of suspect "index" was used in the name to sort of fool people using the 704/709/7040/7090/7094 computers that immediately preceded the System/360 computers. Most of the time when I use BXLE or BXH I have addresses in first operand and the compare register.