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From: glen herrmannsfeldt <gah@ugcs.caltech.edu>
Newsgroups: comp.lang.ada,comp.lang.fortran,comp.lang.pl1
Subject: Re: Why is Ada considered "too specialized" for scientific use
Date: Tue, 8 Jun 2010 12:03:45 +0000 (UTC)
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Date: 2010-06-08T12:03:45+00:00
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In comp.lang.fortran James J. Weinkam <jjw@cs.sfu.ca> wrote:
 
> Your point is well taken for machines of the 60's and 70's, 
> at least for the IBM ones with which I  am most familiar. 
> For example in 360 assembler, if you wanted to add two numbers 
> you had your choice  of A, AR, AH, AP, AL, ALR,  AE, AER, AD, 
> ADR, AXR, AU, AUR, AW, AWR and maybe a few more that I have  
> forgotten. There was a one-to-one correspondence between each 
> of these mnemonics and their  corresponding numerical op codes.
> The assembly language programmer had to choose the correct 
> mnemonic  instruction to suit the circumstances. 

(snip)

And note that the hex value for the opcode for many of those
add instructions has A for its low digit.  Also, the divide
instructions have D for their low hex digit.  Subtract
and multiply come in between, with B and C.

Starting with S/370, some instructions have a two byte opcode.

There are now even more add instructions with 64 bit operations
in z/Architecture, AGR, AGFR, AY, AG, AGF, add logical with
carry ALCR, ALCGR, ALC, ALCG, IEEE binary floating point
operations AEBR, ADBR, and AXBR, and finally decimal floating
point instructions ADTR and AXTR.

-- glen