Here's another form of branch table combining compare and branches. Just
thought it was interesting and one reason why I love assembler. So many
possibilities.
XR R0,R0 INCREMENT = 0
LR R1,R0
BCTR R1,0 SET COMPARE = -1
JXLE R15,R0,LBL_RC_MINUS Label taken if <= -1
LA R1,MAX_RC SET COMPARE = MAX_RC
JXH R15,R0,LBL_RC_GT_MAX Label taken if > MAX_RC
B BRTAB(R15)
BRTAB DS 0H
J LABEL_RC0
J LABEL_RC4
J LABEL_RC8
J LABEL_RC12
-----Original Message-----
From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> On Behalf
Of Seymour J Metz
Sent: Tuesday, November 23, 2021 17:12
To: ASSEMBLER-LIST@LISTSERV.UGA.EDU
Subject: Re: Base-less macros
CAUTION: This message was sent from outside the company. Do not click links or
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In light of subsequent messages, yes.
________________________________________
From: IBM Mainframe Assembler List <ASSEMBLER-LIST@LISTSERV.UGA.EDU> on behalf
of Tony Thigpen <t...@vse2pdf.com>
Sent: Tuesday, November 23, 2021 1:33 PM
To: ASSEMBLER-LIST@LISTSERV.UGA.EDU
Subject: Re: Base-less macros
I think Martin is really commenting that if you only have 3 branch
possibilities, then the overhead of the validation is greater than just doing
three Test-and-branch instruction pairs.
I don't know about others, but I don't usually use a branch table unless I have
8 or more values. Many of my branch tables have 100+ entries.
Tony Thigpen
Seymour J Metz wrote on 11/23/21 12:31 PM:
> ?
>
> What is a shorter way to do the error checking?
>
>
> --
> Shmuel (Seymour J.) Metz
> http://mason.gmu.edu/~smetz3
>
> ________________________________________
> From: IBM Mainframe Assembler List [ASSEMBLER-LIST@LISTSERV.UGA.EDU]
> on behalf of Martin Ward [mar...@gkc.org.uk]
> Sent: Tuesday, November 23, 2021 12:27 PM
> To: ASSEMBLER-LIST@LISTSERV.UGA.EDU
> Subject: Re: Base-less macros
>
> On 23/11/2021 17:12, Seymour J Metz wrote:
>> LTR R15,R15
>> JM BADIX
>> CHI R15,LIMIT
>> JH BADIX
>> TML R15,3
>> JNZ BADIX
>> J *+4(R15)
>> BRTAB EQU *
>> J RC0ROUTINE
>> J RC4ROUTINE
>> J RC8ROUTINE
>> LIMIT EQU *-BRTAB
>
> Three test and branch instruction pairs plus two unconditional branch
> instructions, all to avoid executing a sequence of up to three test
> and branch instruction pairs :-)
>
> --
> Martin
>
> Dr Martin Ward | Email: mar...@gkc.org.uk |
> http://secure-web.cisco.com/1Pzh0mz_8aE1yk4Zn65QdgWKxjXTYuplR0LTSWVThm
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> Fwww.gkc.org.uk G.K.Chesterton site:
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> Fwww.gkc.org.uk%2Fgkc | Erdos number: 4
>
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