Push-Down Instructions - Xerox Sigma 6 Reference Manual

If
011
illl'~lal
digit or sign is detected in the decimal infor-
nlOti,-1f) field, the computer unconditionally aborts execution
of the instl"uction (at the time the illegal digit or sign is en-
countered) and traps to location X'45' with the contents of
register R, register Rul, register 1, the destination byte
string, and the condition code containing the results of the
last editing operation performed before the illegal digit or
si gn was encountered.
In the following examples, the hexadecimal codes for the
digit selector (x'20'), the significance start (X'21 ' ), the
field separation (X'22'), and the immediate significance
start (X '23') are represented by the character groups ds, ss,
fs, and si, respectivel y. Also, the symbol-t5 is used to
represent the character blank (X'40').
Exampl e 1, before executi on:
The instruction word is: X '63600000'
The contents of register 6 are: X'5COOOI00'
The contents of register 7 are: X'OCOOI000'
The contents of the decimal information field beginning at
byte locati on X'l 00' are: 00 00 00
0+
The contents of the desti nation byte string beginni ng at
byte location X'1000' are:
ds ds , ds ds ss . ds ds
1)
C
R
The condition code is: 0000
Example 1, after execution:
The instruction word is unchanged
The new contents of register 6 are: X '5COOOl
04'
The new contents of regi ster 7 are: X '00001 OOC'
The contents of the decimal information field are unchanged
The new contents of the destination byte string are:
* * * * * *
.001)-0-0
The new condition code is: 1000
The contents of register 1 are: X'xxxOl006'
By subsequent programming, a floating dollar sign can be
inserted in front of the first significant character of the
edited byte string by using the contents of register 1, minus
1, as the address of the byte location where the dollar sign
j
s to be inserted.
Fxampl e 2, before execution:
The initial conditions are identical to example 1, except
that the contents of the decimal information field are:
06
54 32 1-
Example 2, after execution:
The instruction word and the decimal field are unchanged
The new contents of registers 6 and 7 are identical to those
given for example 1
The new contents of the destination byte string are
*6,543.2115CR
The new condition code is: 1011
The new contents of register are: X'xxx01001'
Example 3, before execution:
The initial conditions are identical to example 1, except
that the contents of the decimal field are:
00 54 32 1+
Example 3, after executi on:
The instruction word and the decimal field are unchanged
The new contents of registers
6
and
7
are identica
I
to that
given for example 1
The new contents of the destination byte string are
***543.211)1)-0
The new condition code is: 1010
The new contents of register 1 are: X'xxx01003'
Example 4, before execution:
The instruction word is: X '634001 00'
The contents of register 4 are: X'7BOOI000'
The contents of register 5 are: X'19002000'
The contents of the decimal information field beginning at
byte
I
ocati on X' 11 00' are:
06 1'2 50
0+
01 23 4+ 03
5-
The contents of the destination byte string beginning at
byte location X '2000' are:
Adsdssi. dsdsdsfsBdsdsss. dsdsCfsDsidsdsEND
The condition code is: 0100
Example 4, after execution:
The instruction word is unchanged
The new contents of register 4 are: X'7BOOI009'
The new contents of register 5 are: X '00002019'
The decimal information field is unchanged
The new contents of the desti nation byte stri ng are:
# 612.500 # # # 12 . 341> # # 035 END
The new condition code is: 1011
The new contents of register 1 are: X 'xxx020l3'
PUSH-DOWN INSTRUCTIONS
The term "push-down processing" refers to the programming
technique (used extensively in recursive routines) of storing
the context of a calculation in memory, proceeding with a
new set of information, and then activating the previously
stored information. Typically, this process involves a re-
served area of memory (stack) into which operands are
pushed (stored) and from which operands are pulled
{loaded} on a lost-in, first-out basis. The SIGMA 6 computer
Push-Down Instructions 67