John, So your saying in COBOL are you talking about Comp-3 binary ?
Scott ford www.identityforge.com On Jul 14, 2012, at 8:08 AM, John Gilmore <jwgli...@gmail.com> wrote: > Doing integer--as opposed to real fixed-point--arithmetic with > packed-decimal values is the real culprit here. > > Integer arithmetic should never be done with anything but binary > integers. Operations on them are register operations, which are much > faster than storage-to-storage ones; and zero is always positive. > Moreover, it is now possible to make them behave in COBOL exactly as > they do in assembly language. > > John Gilmore, Ashland, MA 01721 - USA > > On 7/14/12, Gibney, Dave <gib...@wsu.edu> wrote: >> Back in 1981, one of the first bugs I had to find/fix was a COBOL (VS?) >> routine intended to distribute the rounding difference to a set of records. >> Perform until zero left to distribute. It looped at negative zero. I didn't >> write it, I don't remember my precise fix. >> >>> -----Original Message----- >>> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] >>> On Behalf Of Frank Swarbrick >>> Sent: Friday, July 13, 2012 3:07 PM >>> To: IBM-MAIN@LISTSERV.UA.EDU >>> Subject: Re: COBOL packed decimal >>> >>> Excellent! Thank you very much! >>> Subtle is right! :-) >>> Negative zero, huh? Must be that new math, thing. :-) >>> >>> Frank >>> >>> >>> >>> >>>> ________________________________ >>>> From: "Dan Skomsky @ Home" <poodles...@sbcglobal.net> >>>> To: IBM-MAIN@LISTSERV.UA.EDU >>>> Sent: Friday, July 13, 2012 3:24 PM >>>> Subject: Re: COBOL packed decimal >>>> >>>> From an old discussion on the same subject from back in '05 over at >>>> http://www.tek-tips.com : >>>> >>>> Here's an explanation of what is happening. When we were converting >>>> from VS COBOL to COBOL II/COBOL 370, I found the book "COBOL/370 FOR >>> VS >>>> COBOL AND COBOL II PROGRAMMERS by Harvey Bookman. Here's what he says >>>> about your question.... >>>> >>>> "One change from VS COBOL to COBOL/370 that may seem quite baffling >>>> occurs when a constant or another COMP-3 data field is added or >>>> subtracted to or from a signed COMP-3 data field. The VS COBOL >>>> compiler produced only an Add Packed (AP) or Subtract Packed (SP) >>>> instruction. COBOL/370 still produces the same instruction but then >>>> issues a Zero and Add Packed (ZAP) of the resulting field into >>> itself. The ZAP is executed for a very subtle reason. >>>> When two negative numbers are added together and an overflow occurs, >>>> the overflow flag in the condition code is turned on while the >>>> resulting sign is set as if overflow did not occur. This means that >>> if >>>> two numbers each defined as PIC S9(03) COMP-3 were added together, and >>>> they had values of -1 and -999 before the addition, the resulting >>> field >>>> would be zero (the digit that overflowed was truncated) with its sign >>>> negative. The ZAP will preserve the sign of all other computations >>> but >>>> will change a zero with a negative sign to a zero with a positive >>> sign." >>>> >>>> "Ensuring a positive sign in a zero result was not necessary in the VS >>>> COBOL compiler. This is because the VS COBOL compiler used a Compare >>>> Packed (CP) instruction to compare numeric fields. It is interesting >>>> that COBOL/370 now often produces a Compare Logical (CLC) instruction >>>> to compare numeric fields. While this is a faster instruction than >>> CP, >>>> it requires the same sign value for an equal condition to occur. For >>>> example, a CP instruction will find fields with hexadecimal values >>> '0F' >>>> and '0C' equal, while the CLC will not." >>>> >>>> The same instructions are generated in Enterprise COBOL as were for >>>> COBOL/370. >>>> >>>> HTH >>>> >>>> -----Original Message----- >>>> From: IBM Mainframe Discussion List [mailto:IBM-MAIN@LISTSERV.UA.EDU] >>>> On Behalf Of Itschak Mugzach >>>> Sent: Friday, July 13, 2012 4:10 PM >>>> To: IBM-MAIN@LISTSERV.UA.EDU >>>> Subject: Re: COBOL packed decimal >>>> >>>> Zero and add pack. >>>> >>>> ITschak >>>> >>>> On Sat, Jul 14, 2012 at 12:05 AM, Frank Swarbrick >>>> <frank.swarbr...@yahoo.com >>>>> wrote: >>>> >>>>> COBOL code >>>>> 77 ws-num-packed pic S9(9) packed-decimal. >>>>> >>>>> add 2 to ws-num-packed >>>>> >>>>> >>>>> Generated assembler: >>>>> >>>>> >>>>> 000014 >>>>> ADD >>>>> 00036A GN=16 EQU >>>>> * >>>>> 00036A FA40 8008 A02C AP 8(5,8),44(1,10) >>>>> WS-NUM-PACKED PGMLIT AT +40 >>>>> 000370 F844 8008 8008 ZAP 8(5,8),8(5,8) WS-NUM- >>> PACKED >>>>> WS-NUM-PACKED >>>>> >>>>> >>>>> What is the purpose of the ZAP? >>>>> >>>>> Thanks, >>>>> Frank >>>>> >>>>> >>>>> -------------------------------------------------------------------- >>> - >>>>> - For IBM-MAIN subscribe / signoff / archive access instructions, >>>>> send email to lists...@listserv.ua.edu with the message: INFO >>>>> IBM-MAIN >>>>> >>>> >>>> ---------------------------------------------------------------------- >>>> For IBM-MAIN subscribe / signoff / archive access instructions, send >>>> email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >>>> >>>> ---------------------------------------------------------------------- >>>> For IBM-MAIN subscribe / signoff / archive access instructions, send >>>> email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >>>> >>>> >>>> >>> >>> ---------------------------------------------------------------------- >>> For IBM-MAIN subscribe / signoff / archive access instructions, send >>> email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >> >> ---------------------------------------------------------------------- >> For IBM-MAIN subscribe / signoff / archive access instructions, >> send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN >> > > ---------------------------------------------------------------------- > For IBM-MAIN subscribe / signoff / archive access instructions, > send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
