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The PowerPC architecture allows an fcmpu or fcmpo instruction with the Rc bit set to
produce a boundedly-undefined result, which may include an illegal instruction program
exception. In the MPC750, crfD should be treated as undefined
2.3.4.2.5 Floating-Point Status and Control Register Instructions
Every FPSCR instruction appears to synchronize the effects of all floating-point
instructions executed by a given processor. Executing an FPSCR instruction ensures that all
floating-point instructions previously initiated by the given processor appear to have
completed before the FPSCR instruction is initiated and that no subsequent floating-point
instructions appear to be initiated by the given processor until the FPSCR instruction has
completed. The FPSCR instructions are summarized in Table 2-31.
Table 2-31. Floating-Point Status and Control Register Instructions
Name
Mnemonic
Syntax
Move from FPSCR
mffs (mffs.)
frO
Move to Condition Register from FPSCR
mcrls
crlO,crlS
Move to FPSCR Field Immediate
mtfsfi (mtfsti.)
crlO,IMM
Move to FPSCR Fields
mtfsf (mtfst.)
FM,frB
Move to FPSCR Bit
a
mtfsbO (mtfsbO.)
crbO
Move to FPSCR Bit 1
mtfsb1
(mtfsb1.)
crbO
Implementation Note-The PowerPC architecture states that in some implementations,
the Move to FPSCR Fields (mtfsf) instruction may perform more slowly when only some
of the fields are updated as opposed to all of the fields. In the MPC750, there is no
degradation of performance.
2.3.4.2.6 Floating-Point Move Instructions
Floating-point move instructions copy data from one FPR to another. The floating-point
move instructions do not modify the FPSCR. The CR update option in these instructions
controls the placing of result status into CR1. Table 2-32 summarizes the floating-point
move instructions.
Table 2-32. Floating-Point Move Instructions
Name
Mnemonic
Syntax
Floating Move Register
fmr (fmr.)
frD,frB
Floating Negate
fneg (fneg.)
frO,trB
Floating Absolute Value
fabs (fabs.)
frO,frB
Floating Negative Absolute Value
fnabs (fnabs.)
frD,frB
2-44
MPC750 RISC Microprocessor User's Manual
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