IBM PowerPC 604 User Manual page 84

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standard 754-1985, IEEE Standard for Binary Floating Point Arithmetic. Detailed
information about the floating-point execution model can be found in Chapter 3, "Operand
Conventions," in The Programming Environments Manual.
The 604 supports non-IEEE mode whenever FPSCR[29] is set. In this mode, denormalized
numbers, NaNs, and some IEEE invalid operations are treated in a non-IEEE conforming
manner. This is accomplished by delivering results that approximate the values required by
the IEEE standard. Table 2-7 summarizes the conditions and mode behavior for operands.
Table 2-7. Floating-Point Operand Data Type Behavior
Operand A Operand B
Operand C IEEE Mode Non·IEEE Mode
Data Type Data Type
Data Type (NI: 0)
(NI= 1)
Single denormalized Single denormalized Single denormalized
Normalize all three Zero all three
Double denormalized Double denormalized Double denormalized
Single denormalized Single denormalized Normalized or zero Normalize A and B Zero A and B
Double denormalized Double denormalized
Normalized or zero
Single denormalized
Single denormalized Normalize B and C ZeroBandC
Double denormalized
Double denormalized
Single denormalized Normalized or zero Single denormalized Normalize A and C Zero A and C
Double denormalized Double denormalized
Single denormalized Normalized or zero Normalized or zero Normalize A Zero A
Double denormalized
Normalized or zero Single denormalized Normalized or zero Normalize B ZeroB
Double denormalized
Normalized or zero Normalized or zero Single denormalized Normalize C ZeroC
Double denormalized
SingleQNaN Don't care Don't care
QNaNl1[
QNaN1 1 1
SingleSNaN
Double ONaN
DoubleSNaN
Don't care SingleQNaN Don't care
QNaNl1J
QNaN1 1 1
Single SNaN
Double QNaN
Double SNaN
Don't care Don't care SingleQNaN
QNaNl1J
QNaN1 1 1
SingleSNaN
DoubleQNaN
DoubleSNaN
Single normalized Single normalized Single normalized Do the operation Do the operation
Single infinity
Single infinity
Single infinity
Single zero
Single zero Single zero
Double normalized Double normalized Double normalized
Double infinity Double infinity Double infinity
Double zero Double zero Double zero
1 Prioritize according to Chapter 3, "Operand Conventions," in
The Programming Environments Manual.
2-18
PowerPC 604 RISC Microprocessor User's Manual