Deleting A High Order Word - HP 3000 III Series Manual

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Mode and Displacement
Machine Instructions and Stack Operations
STOR Store TOS Into Memory
~
O ' 1 0 1 X 1 1
,
The content of the TOS is stored into the effective address mem-
ory location, and is then deleted from the stack.
Memory opcode: 05, bit 6 = 1
Indicators: Unaffected
Addressing modes: DB+, Q+, Q-, S- relative
Dire ct or ind ire ct
Indexing available
Traps: STUN, BNDV
4-16. Instruction Commentary
1. MPYL, MPY, DTST, FIXR, FIXT, LMPY. These six instructions
provide for the deletion of the most significant word of a
doubleword result. The assumption is that the result of the in-
struction (e.g., multiplication product) does not require more
than 16 bits to represent it. The MPY instruction deletes auto-
matically during execution; the remaining five instructions
simply test the result and provide an indication (Carry bit) to
note whether or not the low order word fully represents the t~ue
resu~t. Thus, for these five, the programmer may choose to In-
sert a delete sequence (see figure 4-6) to delete the high order
word if it is insignificant.
Sign of a Sign of a
Double-length Single-length
Integer Integer
/ /
o
15 0 15
IIIIII I I I II II II I III III I I II II III III
OOOOOOOOOOOO'OOOOOX--------------X
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 X - - - - - - - - - - - - - - X
'-------v-------) ''- ....--_ _
.--J
High Order
17 Bits
Example delete sequence:
Significant
Data Bits
MPYL;
Bey· +2;
DELB;
Figure 4-6. Deleting A High Order Word
For MPYL, DTST, FIXR, FIXT, and LMPY, the Carry bit is cleared if
the high order 17 bits are all zeros or all ones. This test en-
sures that the sign bit of the single-length result will be the
same as the sign of the double-length resul t. If this is not the
4-21