>(after I wrote) >> The book "Computer Architecture: Concepts and Evolution" by >> Blaauw and Brooks has many descriptions on how instructions got >> to be the way they did.
>> The book covers a wide variety of machines, though S/360 is >> a favorite example. (Blaauw was the main designer of S/360, >> so it isn't so surprising.) >> There is a small description of EDIT in section 5.1.3. >> They trace back to "Store for Print" on the 702. >> Then explain that EDIT >The instruction is ED, not EDIT,; its companion is EDMK. You want to argue with Blaauw on the name of an S/360 instruction? The instruction is EDIT, the assembler nmemonic is ED. >> is rarely used by COBOL or Fortran >> for print conversions, >That's probably because the instruction was optional >on the small early models of S/360 >and the software was written to use basic instructions. >Nevertheless, there's no reason for not using it, >because the small machines that didn't have those instructions >have long since passed to computer heaven. For hand coded assembler, it isn't bad, but for high-level languages it is easier to write a software loop than to conform to the instruction. Much of S/360, as with VAX, was designed around assembler programmers. Later it was found that compilers only generated a small fraction of the instruction set on most machines. >That said, I understand that IBM 360 compilers didn't use TRT, >which IIRC was a standard instruction. >BTW, EDMK was used for all decimal output in the optimising >XPL compiler. >> and that it is best that it should be left out of instruction sets. >A bad recommendation, because so much is done by ED and EDMK, >and with little effort and even less overhead compared with alternatives. A reasonable cost/benefit analysis of the actual use, done some years later. >> If you like asking questions like that, especially for a variety >> of different machines, you should get the book. >I wouldn't bother, if that is the level of its advice. If you don't believe Blaauw regarding S/360, then who do you believe? -- glen
