How does the ED instruction work?
This is from a post on the Assembler mailing list on 2000-01-08 by John Murray EDIT (ED) is one of the most feared instructions of the original S/360 instruction set. Even career (professional) programmers have shied away from ED, many developing complex macro instructions and/or subroutines to shield them from this poor instruction’s use. As it turns out, and if you ignore all the BS about “field separators” (nobody ever uses them, it was perhaps a good idea that went astray or perhaps temporary insanity on the part of the original hardware engineers), ED turns out to be a fairly nice and easy to use instruction. There are no pointers involved. The EDMK (Edit and Mark instruction can feedback an address that tells you where the first significant digit is, but not edit). The edit instruction has target and source fields like many other SS instructions. The target is the first operand which must contain the edit pattern (or mask) before the instruction is executed. The edit pattern is t
