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4–130 Alpha Architecture Handbook
4.10.24 VAX Floating Subtract
Format:
Operation:
Fc ← Fav - Fbv
Exceptions:
Instruction mnemonics:
Qualifiers:
Description:
The subtrahend operand in register Fb is subtracted from the minuend operand in register Fa
and the difference is written to register Fc.
The difference is rounded or chopped to the specified precision and then the corresponding
range is checked for overflow/underflow. The single-precision operation on canonical sin-
gle-precision values produces a canonical single-precision result.
An invalid operation trap is signaled if either operand has exp=0 and is not a true zero (that is,
VAX reserved operands and dirty zeros trap). The contents of Fc are UNPREDICTABLE if
this occurs.
See Section 4.7.7 for details of the stored result on overflow or underflow.
SUBx Fa.rx,Fb.rx,Fc.wx
!Floating-point Operate format
Invalid Operation
Overflow
Underflow
SUBF Subtract F_floating
SUBG Subtract G_floating
Rounding: Chopped (/C)
Trapping: Exception Completion (/S)
Underflow Enable (/U)