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performed as if the fractions were positive.
I
If
rounding causes a carry out of the leftmost
hexadecimal digit position of the fraction, the
fraction is shifted right one digit position so that
the carry becomes the leftmost digit of the fraction,
and the characteristic is increased by one.
The sign of the result is the same as the sign of
I
the second operand. There is no normalization to
eliminate leading zeros.
An exponent-overflow exception exists when
shifting the fraction right would cause the
characteristic to exceed 127. The operation is
completed by loading a number whose
characteristic is 128 less than the correct value, and
a program interruption for exponent overflow
occurs. The result is normalized, and the sign and
fraction remain correct.
Exponent-underflow and significance exceptions
cannot occur.
The Rl field must designate register 0, 2, 4, or 6;
the R
z
field of LRER must designate register 0, 2,
4, or 6; and the R
z
field of LRDR must designate
register
°
or 4. Otherwise, a specification
exception is recognized.
Condition Code: The code remains unchanged.
Program Exceptions:
Exponent Overflow
Specification
MULTIPLY
MER
R1,R2
[RR, Short Multiplier and Multiplicand,
Long Product]
, 3C'
I
R 1
I
R2
I
o
8
12
15
ME
R1,D2(X2,B2)
[RX, Short Multiplier and Multiplicand,
Long Product]
o
8
12
16
20
31
MDR
[RR, Long Operands]
o
8
12
15
9-1Z
IBM 4300 Processors Principles of Operation
MD
[RX, Long Operands]
o
8
12
16
20
31
MXDR
R1,R2
[RR, Long Multiplier and Multiplicand,
Extended Product]
'27'
R1
I
R2
I
o
8
12
15
MXD
R1,D2(X2,B2)
[RX, Long Multiplier and Multiplicand,
Extended Product]
'67'
o
8
12
16
20
31
[RR, Extended Operands]
'26'
o
8
12
15
The normalized product of the second operand (the
multiplier) and the first operand (the multiplicand)
is placed in the first-operand location.
Multiplication of two floating-point numbers
consists in exponent addition and fraction
multiplication. The operands are first normalized
to eliminate leading hexadecimal zeros. The sum of
the characteristics of the normalized operands, less
64, is used as the characteristic of the intermediate
product.
The fraction of the intermediate product is the
exact product of the normalized operand fractions.
When the intermediate-product fraction has one
leading hexadecimal zero digit, the fraction is
shifted left one digit position, bringing the contents
of the guard-digit position into the rightmost
position of the result fraction, and the
intermediate-product characteristic is reduced by
one. The fraction is then truncated to the proper
result-fraction length.
For MER and ME, the multiplier and
multiplicand fractions have six hexadecimal digits;
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