On 7 Nov 2006 10:34:33 -0800, in bit.listserv.ibm-main you wrote: >-----Original Message----- >From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] >Behalf Of Richard Tsujimoto >Sent: Tuesday, November 07, 2006 9:15 AM >To: [email protected] >Subject: Re: Assembler question > >Is *discontinuity in assembler design* a nice way of saying, it's a bad >design? I would think a length of 1 and 0 are different, >and MVC should perform accordingly, e.g. if length=0, do nothing. > ><snip> > >Since the length for MVC is 8 bits, L=0 means to move 1 byte (aka >Machine length). Should you take that number negative, you would get FF >which is 256 bytes (since byte 0 must be counted).
The length as specified in the assembler code gets decremented by 1 for the machine code (1 - 256 -> 0 - 255). Thus if the assembler length factor is calculated as less than one before decrementing, the assembler should have been designed to flag that as an error. Given history, that flagging would have to be optional. Back in the 1980's or early 1990's, with the help of John Ehrman I submitted a number of requirements at SHARE, on of which was for optional flagging of all operand mismatches including length matches, LH of a fullword, etc. Even though they were all rejected at the time, many of them later made it into what became HLASM. Maybe it is my COBOL background but the idea that the operation and the data definition should match in most cases is one that the assembler should encourage. In regard to another thread, the awkwardness of coding reentrant code and the mediocre support for it means that for main programs, I don't bother. I do for exits and subroutines. > >And you can't not generate the D2llBDDDBDDD, because you are allowed to >come back and modify the storage used by the MVC. You may also EXecute >this instruction... > >Just remember, this is a LOW LEVEL language, not a mid/hi level >language. > >Later, >Steve Thompson ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
