o 8 12 15
DE
DDR [RR, long Operands]
o 8 12 15
The first operand (the dividend) is
divided by the second operand (the divi
sor), and the normalized quotient is
placed at the first-operand location.
Floating-point division consists in
characteristic subtraction and fraction
division. The operands are first
normalized to eliminate leading hexade
cimal zeros. The difference between the
dividend and divisor characteristics of
the normalized operands, plus 64, is
used as the characteristic of an inter
mediate quotient.
All dividend and divisor fraction digits
participate in forming the fraction of
the intermediate quotient. The
intermediate-quotient fraction can have
no leading hexadecimal zeros, but a
right shift of one digit position may be
necessary with an increase of the char
acteristic by one. The fraction is then
truncated to the proper result-fraction
length.
An exponent-overflow exception is recog
nized when the characteristic of the
final quotient would exceed 127 and the
fraction is not zero. The operation is
completed by making the characteristic
128 less than the correct value. The
result is normalized, and the sign and
fraction remain correct. A program
interruption
occurs.
for exponent overflow
An exponent-underflow exception exists
when the characteristic of the final
quotient 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 character
istic 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, a program
interruption does not take place;
instead, the operation is completed by
making the quotient a true zero.
Exponent underflow does not occur when
an operand characteristic becomes less
than zero during normalization of the
operands or when the intermediate
quotient characteristic is less than
zero, as long as the final quotient can
be represented with the correct charac
teristic.
When the divisor fraction is zero, a
floating-point-divide exception is
recognized. This includes the case of
division of zero by zero.
When the dividend fraction is zero, but
the divisor fraction is nonzero, the
quotient is made a true zero. No expo
nent overflow or exponent underflow
occurs.
The sign of the quotient is determined
by the rules of algebra, except that the
sign is always plus when the quotient is
made a true zero.
The Rt and R2 fields must designate
register
specification exception is recognized.
Condition Code:
unchanged.
The code remains
Access (fetch, operand 2 of DD and
DE only)
Exponent overflow
Exponent underflow
Floating-point divide
Operation (if the floating-point
facility is not installed>
Specification
Examples of the use of the
Chapter 9. Floating-Point Instructions 9-9