RCA 70/46 Reference Manual page 152

Multiply Halfword
(MH)
General Description
Format
(RX)
Condition Code
Interrupt Action
Notes
Fixed-Point
Instructions
• The operand (multiplicand) specified by the first address (R
1 )
is
multiplied by the halfword operand (multiplier) specified by the second
address (XdB
2
/D
2 ) .
The product of the operands replaces the contents of
the register specified by the first address (R
1 )
o
7 8 11 12 15 16 19 20
31
• Unchanged.
• Address error:
Addressing.
Specification.
• 1. The halfword operand in main memory is expanded to a full word
before multiplication by propagating the sign bit value through the
16 high-order positions. Both operands are considered as 32-bit
signed integers. The multiplicand is replaced by the low order 32 bits
of the product. The product usually occupies 46 bits of significance
except when both operands are maximum negative numbers and
occupy 47 bits.
2. The bits to the left of the 32 low-order bits of the product are not
tested for significance. No overflow indication is given. Since the
bits to the left of the low-order 32 are ignored, the sign of the result
may differ from the true sign of the product, if the product exceeds
32 bits.
3. The operand specified by the second address is unaltered.
4. A zero product is always positive.
143