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the product fraction has the full 14 digits of the
long format, with the two rightmost fraction digits
always zeros. For MDR and MD, the multiplier
and multiplicand fractions have 14 digits, and the
final product fraction is truncated to 14 digits. For
MXDR and MXD, the multiplier and multiplicand
fractions have 14 digits, with the multiplicand
occupying the high-order part of the first operand;
the final product fraction contains 28 digits and is
an exact product of the operand fractions. For
MXR, the multiplier and multiplicand fractions
have 28 digits, and the final product fraction is
truncated to 28 digits.
An exponent-overflow exception is recognized
when the characteristic of the final product would
exceed 127 and the fraction is not zero. The
operation is completed by making the characteristic
128 less than the correct value. If, for extended
results, the low-order characteristic would also
exceed 127, it, too, is decreased by 128. The result
is normalized, and the sign and fraction remain
correct. A program interruption for exponent
overflow occurs.
Exponent overflow is not recognized when the
intermediate-product characteristic is initially 128
but is brought back within range by normalization.
An exponent-underflow exception exists when
the characteristic of the final product would be less
than zero and the fraction is not zero. If the
exponent-underflow mask bit is one, the operation
is completed by making the characteristic 128
greater than the correct value, and a program
interruption for exponent underflow occurs. The
result is normalized, and the sign and fraction
remain correct. If the exponent-underflow mask
bit is zero, program interruption does not take
place; instead, the operation is completed by
making the product a true zero. For extended
results, exponent underflow is not recognized when
the low-order characteristic would be less than zero
but the high-order characteristic is equal to or
greater than zero.
Exponent underflow does not occur when the
characteristic of an operand becomes less than zero
during normalization of the operands, as long as
the final product can be represented with the
correct characteristic.
When either or both operand fractions are zero,
the result is made a true zero, and no exponent
overflow or exponent underflow occurs.
The sign of the product is determined by the
rules of algebra, except that the sign is always zero
when the result is made a true zero.
The Rl field for MER, ME, MDR, and MD, and
the R2 field for MER, MDR, and MXDR must
designate register 0, 2, 4, or 6. The Rl field for
MXDR, MXD, and MXR, and the R2 field for
MXR must designate register
°
or 4. Otherwise, a
specification exception is recognized.
Condition Code: The code remains unchanged.
Program Exceptions:
Access (fetch, operand 2 of ME, MD, and MXD
only)
Exponent Overflow
Exponent Underflow
Specification
Programming Note
Interchanging the two operands in a floating-point
multiplication does not affect the value of the
product.
STORE
STE
[RX, Short Operands]
o
8
12
16
20
31
STO
[RX, Long Operands]
o
8
12
16
20
31
The first operand is placed unchanged in the
second-operand location.
The Rl field must designate register 0, 2, 4, or 6;
otherwise, a specification exception is recognized.
Condition Code: The code remains unchanged.
Program Exceptions:
Access (store, operand 2)
Specification
Chapter 9. Floating-Point Instructions
9-13
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