Right. Given that we only have 8 bits to represent 1-256 bytes, it would be represented as X'00'-X'FF' in the instruction. I see the discontinuity in design. But, given the coding example where the target is 1 byte in length, a warning by the assembler might be nice, but IMHO, the responsibility lies with the programmer using (stylistically, or otherwise) his knowledge of the tools as he/she fits.
Tom Marchant <[EMAIL PROTECTED]> Sent by: IBM Mainframe Discussion List <[email protected]> 11/07/2006 10:31 AM Please respond to IBM Mainframe Discussion List <[email protected]> To [email protected] cc Subject Re: Assembler question On Tue, 7 Nov 2006 10:14:38 -0500, Richard Tsujimoto <[EMAIL PROTECTED]> wrote: >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. > No. The assembler decrements the specified length by 1 and stores the value in the MVC instruction. Read the POO. MVC is designed to move from 1 to 256 bytes using an 8 bit length. If the instruction is coded with a length of zero, that length is not decremented, but stored in the MVC instruction. I believe that's the discontinuity to which Gil refers. Length of zero is frequently coded on a MVC that is to be used as the target of EXecute. -- Tom Marchant ---------------------------------------------------------------------- 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 ---------------------------------------------------------------------- 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
