Divide - IBM 4300 Manual

COMPARE
[RR, Short Operands]
o
8
12 15
CE
[RX, Short Operands]
179
I
I
R 1
I
X2
I
B2
o
8
12 16
20 31
CDR [RR, Long Operands]
o
8
12 15
CD [RX, Long Operands]
169
I
I
R
1
I
X2
I
B2
o
8
12 16
20 31
The first operand is compared with the second
operand, and the condition code is set to indicate
the result.
The comparison is algebraic and follows the
procedure for normalized floating-point
subtraction, except that the difference is discarded
after setting the condition code and both operands
remain unchanged. When the difference, including
the guard digit, is zero, the operands are equal.
When a nonzero difference is positive or negative,
the first operand is high or low, respectively.
An exponent-overflow, exponent-underflow, or
significance exception cannot occur.
The Rl and R2 fields must designate register 0,
2, 4, or 6; otherwise, a specification exception is
recognized.
Resulting Condition Code:
°
Operands are equal
1 First operand is low
2 First operand is high
3
Program Exceptions:
Access (fetch, operand 2 of CE and CD only)
Specification
9-8 IBM 4300 Processors Principles of Operation
Programming Notes
1. An exponent inequality alone is not sufficient
to determine the inequality of two operands
with the same sign, because the fractions may
have different numbers of leading hexadecimal
zeros.
2. Numbers with zero fractions compare equal
even when they differ in sign or characteristic.
DIVIDE
[RR, Short Operands]
o
8
12 15
DE
R1,D2(X2,B2) [RX, Short Operands]
I
7D
I
I
R 1
I
X2
I
B2
I
D2
o
8
12 16
20 31
[RR, Long Operands]
o
8
12 15
DD R1,D2(X2,B2) [RX, Long Operands]
I
6D
I
I
R 1
I
X2
I
B2
I
D2
o
8
12 16 20 31
The first operand (the dividend) is divided by the
second operand (the divisor), and the normalized
quotient is placed in the first-operand location. No
remainder is preserved.
Floating-point division consists in characteristic
subtraction and fraction division. The operands are
first normalized to eliminate leading hexadecimal
zeros. The difference between the dividend and
divisor characteristics of the normalized operands,
plus 64, is used as the characteristic of an
intermediate 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
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