Here's a single DC instruction I've posted May 2003 [search for "what's your
most difficult assembler concept"]
BYTE_FLIP DS 0CL256
T DC 256AL1((((*-T)/001)-((*-T)/002)*2)*X'80'++++++++++++++++++++++++
(((*-T)/002)-((*-T)/004)*2)*X'40'++++++++++++++++++++++++
(((*-T)/004)-((*-T)/008)*2)*X'20'++++++++++++++++++++++++
(((*-T)/008)-((*-T)/016)*2)*X'10'++++++++++++++++++++++++
(((*-T)/016)-((*-T)/032)*2)*X'08'++++++++++++++++++++++++
(((*-T)/032)-((*-T)/064)*2)*X'04'++++++++++++++++++++++++
(((*-T)/064)-((*-T)/128)*2)*X'02'++++++++++++++++++++++++
(((*-T)/128)-((*-T)/256)*2)*X'01')
HTH,
-Victor-
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The macro at the end of my reply will generate a reverse translate table. I
tested it enough to see that it looked right but it has nothing to do with
my original point. I've found this discussion interesting and it has given
me reason to play with something other than the complex process I'm working
on now. My original point, as was taken by Charles, was that I prefer
automatic processes to generate anything but the simplest translate tables.
I prefer to do it in a program and copy it from a dump into a program
because the table is static. I don't need to generate it every time I
assemble.
In regards to TROO, the original problem was stated as translating a 64 bit
register. A STG, TR for 8 bytes, followed by a LRVG will more than suffice.
Though, I find your argument about the use of a TRTRE to simulate a FROGR
interesting. It brings the whole bit reversal into perspective. I'm not a
big fan of translate instructions (I use them often enough), particularly
those that require facilities and facility enhancements, unless you're
translating "long" strings and are willing to test the facility bits. I'm
sure that the translation and parsing facilities exist on most customer's
boxes by now but I emphasize "most". When I awakened this morning, I wrote
an algorithm to do a load reverse bytes and bits using FLOGR to drive the
process. I'm going to give the idea of a FROGR simulation more thought and
continue this exercise later.
MACRO
&LABEL REVTABLE ,
* Construct reverse bits translate table
LCLA &I,&J,&K,&L,&M,&N,&O
LCLC &X
&LABEL DS 0D LIKE EM DOUBLE WORD ALIGNED
&I SETA 0 STARTING VALUE
.TABLOOP ANOP LOOP UNTIL TABLE IS DONE
&K SETA 1 NEED SIXTEEN ENTRIES PER LINE
&X SETC 'AL1('
AGO .X16LP
.X16NXT ANOP
&X SETC '&X'.'&J'.','
.X16LP ANOP 16 ENTRY LOOP
&J SETA 0 STARTING RESULT
&L SETA 1 STARTING ADDEND
&M SETA 1 8 BITS PER BYTE
&N SETA 128 STARTING COMPARAND X'80'
&O SETA &I COPY CURRENT BYTE TO REVERSE
.BYTELP ANOP
AIF (&O LT &N).BYTEFT LESS THAN CURRENT - 0
&O SETA &O-&N
&J SETA &J+&L
.BYTEFT ANOP
&L SETA &L*2 NEXT ADDEND
&N SETA &N/2 NEXT COMPARAND
&M SETA &M+1 NEED EIGHT BITS
AIF (&M LE 8).BYTELP
&I SETA &I+1
&K SETA &K+1
AIF (&K LE 16).X16NXT
&X SETC '&X'.'&J'.')'
DC &X
AIF (&I LT 256).TABLOOP
MEND
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