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is dupl icated throughout the remainder of the byte string
(see "Case III", below).
Affected: (OBS), (R), (Ru 1)
(S8S)- OBS
If MBS is indirectly addressed, it is treated as a nonexistent
instruction, in which case the computer unconditionally
aborts execution of the instruction (at the time of operation
code decoding) and traps to location X ' 40 ' with the contents
of register R and the destination byte string unchanged.
A speed advantage can be gained in the MBS instruction if
the source and destination byte strings both begin on the
same byte within their respective words.
This allows all
bytes (except passibly the first few bytes and the last few
bytes to be moved in fullword units.
Case I: even, nonzero R field (Ru1=R+l)
Contents of register R:
Contents of reg i ster R+ 1 :
The source byte string begins with the byte location pointed
to by the source address in register R plus the displacement
in MBS; the destination byte string begins with the byte lo-
cation pointed to by the destination address in register R+1.
Both byte strings are C bytes in length.
When the instruc-
tion is completed, the destination and source addresses are
each incremented by C, and C is set to zero.
Case II: odd R field (Rul=R)
Contents of regi ster R:
The source byte string begins with the byte location pointed
ta by the address in register R plus the displ acement in
MBS; the destination byte string begins with the byte lo-
cation pointed to by the destination address in register R.
Both byte strings are C bytes in length. When the instruc-
tion is completed, the destination address is incremented by
C, and C is set to zero.
Case III: zero R field (Rul=l)
Contents of register
The source byte string consists of a single byte, the contents
of the byte location pointed to by the displacement in MBS;
the destination byte string begins with the byte location
62
Byte-String Instructions
pointed to by the destination address in register 1 and is C
bytes in length.
In this case, the source byte is duplicated
throughout the destination byte string. When the instruction
is completed, the destination address is incremented by C
and C is set to zero.
CBS
COMPARE BYTE STRING
(Immediate displacement, continue after interrupt)
COMPARE BYTE STRIN G compares, as magnitudes, the con-
tents of the source byte string with the contents of the des-
tination byte string, byte by corresponding byte, beginning
with the first byte of each string. The comparison continues
until the specified number of bytes have been compared or
until an inequality is found.
When CBS terminates, CC3
and CC4 are set to indicate the result of the last comparison.
If
the CBS instruction terminates due to inequality, the count
in register Ru 1 is one greater than the number of bytes re-
maining to be compared; the source address in register Rand
the destination address in register Ru1 indicate the locations
of the unequal bytes.
Affected: (R), (Ru 1 ), CC3, CC4
(SBS) : (OBS)
Condition code settings:
2
3
4
o
0
o
o
Result of CBS
source byte string equals destination
byte string
source byte stri I1g I ess than desti nation
byte stri ng
source byte string greater than destination
byte string
If
CBS is indirectly addressed, it is treated as a nonexistent
instruction, in which case the computer unconditionally
aborts execution of the instruction (at the time of operation
code decoding) and traps to location X ' 40 ' with the contents
of register R and the destination byte string unchanged.
Case I: even, nonzero R field (Ru1=R+l)
Contents of register R
Contents of register R+ 1
The source byte string begins with the byte location
pointed to by the source address in register R plus the
displacement in CBS; the destination byte string begins
with the byte location poi nted to by the desti nation ad-
dress in register R+ 1.
Both byte strings are C bytes in
length.
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