Instructions - IBM 4300 Manual

2. In the absence of an exponent overflow or
exponent underflow, the long floating-point
number constituting the low-order part of an
extended result correctly expresses the value of
the low-order part of the extended result when
the characteristic of the high-order part is 14 or
higher. This applies also when the result is a
true zero. When the high-order characteristic
is less than 14 but the number is not a true
zero, the low-order part, when addressed as a
long floating-point number, does not have the
correct characteristic value.
3. The entire fraction of an extended result
participates in normalization. The low-order
part alone mayor may not appear to be a
normalized long floating-point number,
depending on whether the 15th digit of the
normalized 28-digit fraction is nonzero or zero.
Instructions
The floating-point instructions and their
mnemonics, formats, and operation codes are listed
in the figure "Summary of Floating-Point
Instructions." The figure also indicates when the
condition code is set and the exceptional conditions
in operand designations, data, or results that cause
a program interruption.
9-4 IBM 4300 Processors Principles of Operation
Mnemonics for the floating-point instructions
have an R as the last letter when the instruction is
in the RR format. For instructions where all
operands are the same length, certain letters are
used to represent operand-format length and
normalization, as follows:
E short normalized
U short unnormalized
D long normalized
W long unnormalized
X extended normalized
Note: In the detailed descriptions of the individual
instructions, the mnemonic and the symbolic
operand designation for the assembler language are
shown with each instruction. For a
register-to-register operation using LOAD (short),
for example, LER is the mnemonic and R j,R
2
the
operand designation.