AT&T 3B2/300 Technical Reference Manual page 368

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OP2
OP3
Bits 06-04 is the Operand Specifier 2 (OP2) field. OP2 specifies whether the
second source operand is a MAU register, a memory-based operand of a given size,
or nonexistent (no operand). The value of this field is as follows.
BITS 06 - 04 OPERAND LOCATION
000 REGISTER FO OR F4 (DEPENDING ON RB2)
001 REGISTER Fl OR FS (DEPENDING ON RB2)
010 REGISTER F2 OR F6 (DEPENDING ON RB2)
011 REGISTER F3 OR F7 (DEPENDING ON RB2)
100 MEMORY-BASED SINGLE WORD
101 MEMORY-BASED DOUBLE WORD
110
MEMORY-BASED TRIPLE WORD
111
NO OPERAND
Bits 03-00 are the Operand Specifier 3 (OP3) field. OP3 specifies whether the
destination operand is a MAU register, a memory-based operand of a given size, or
nonexistent (no operand). Even though the register destinations are specified as
single, double, or double-extended, the result is stored in the registers in
double-extended precision. The precision designations are used for rounding and
checking for underflow and overflow. The value of this field is as follows.
OPERAND DESTINATION
BITS 03 - 00
REGISTER PRECISION
0000
FOOR F4 SINGLE
0001 Fl OR FS SINGLE
0010 F2 OR F6 SINGLE
0011 F3 OR F7 SINGLE
0100 FOOR F4 DOUBLE
0101 Fl OR FS DOUBLE
0110 F2 OR F6 DOUBLE
0111 F3 OR F7 DOUBLE
1000 FOOR F4 DOUBLE-EXTENDED
1001
Fl OR FS DOUBLE-EXTENDED
1010
F2 OR F6 DOUBLE-EXTENDED
1011 F3 OR F7
DOUBLE-EXTENDED
1100 - MEMORY-BASED SINGLE WORD
1101 -
MEMORY-BASED DOUBLE WORD
1110
-
MEMORY-BASED TRIPLE WORD
1111 - NO OPERAND
FUNCTIONAL DESCRIPTION 3-115