I see it's not as simple as I thought. Maybe if it's negative, zero the sign bit with an "And", divide by 256, then "Or" the quotient with hex 00800000 to recover the dropped bit.
Bill On Wed, 21 Feb 2007 14:43:51 -0800, Charles Mills wrote: >Thanks. Without the R6 = R6 - 1 it's definitely wrong most of the time. >That's the difference between 1's complement and 2's complement arithmetic. >(I think your -512 is a particularly favorable boundary case with no >remainder.) > >-1 \ 256 = 0 (with a remainder of -1). > >That would give you x'FFFFFFFF' going to 0. > >So I need to do something else also, but I'm not sure what. Anyone? (BTW, my >apologies for the extra blank lines in the OP -- Outlook strikes again!) > >Charles > >-----Original Message----- >From: IBM Mainframe Discussion List [mailto:[EMAIL PROTECTED] On Behalf >Of Bill Godfrey >Sent: Wednesday, February 21, 2007 2:26 PM >To: [email protected] >Subject: Re: Simulating SRL in integer arithmetic > >On Wed, 21 Feb 2007 10:48:10 -0800, Charles Mills wrote: > >> ' Simulate a shift right logical 8 >> If R6 >= 0 Then >> R6 = R6 \ 256 ' \ is integer division >> Else >> R6 = R6 \ 256 ' \ is integer division >> R6 = R6 - 1 >> R6 = R6 And &HFFFFFF ' Equivalent to S/390 X'FFFFFF' >> End If > >I don't think you want the "R6 = R6 - 1". And if you drop it, you may as >well rethink whether you want the if/else at all, and just do the "And" >whether it's needed or not. > >I'm not a mathematician, nor do I know Visual Basic, but the result >produced by this VBS script may be relevant. > >R6 = -512 >R6 = R6 \ 256 And &Hffffff >Wscript.echo R6 > >I'm pretty sure this script uses signed 32-bit integers, because it won't >run if i try to set R6 to a value > 2147483647. I picked -512 (hex >fffffe00) as a test value, expecting a result of hex 00fffffe which is >decimal 16777214, and 16777214 is indeed the result displayed by "cscript >srl.vbs" from the command prompt. > ---------------------------------------------------------------------- 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
