Intel i86W Manual page 213

INSTRUCTION FORMAT AND ENCODING
When srcl is immediate and bit 28 is set, bit zero of the immediate value is forced to
zero.
For
fld, fst, pfld, pst,
and
flush,
bit 0 selects autoincrement addressing if set. Bits one and
two select the operand size as follows:
Bit 1 Bit 2 Operand Size
0 0 64-bits
0 1 128-bits
1
0 32-bits
1
1 32-bits
When srcl is immediate, bits zero and one of the immediate value are forced to zero to
maintain alignment. When bit one of the immediate value is clear, bit two is also forced
to zero.
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