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FST             Store real                           Exceptions: I O U P
FSTP            Store real and pop                   C3 C2 C1 C0: ? ? * ?

FST destination
FSTP destination

                ; FST dest              ; FSTP dest
        Logic   destination . ST        destination . ST
                                        pop ST

    FST copies the value in ST to the destination which can be another
    register or a single or double real memory operand. FSTP copies and
    then pops ST; it also accepts an extended real memory operand.


    Note
    If the destination is single or double real, the significand is
    rounded to the width of the destination (according to the RC field
    of the control word) and the exponent is converted to the width and
    bias of the destination format. The instructions also check for the
    over/underflow condition.
    If ST contains zero, infinity, or a NaN, the significand is not
    rounded but chopped on the right to fit the destination. The
    exponent is also chopped on the right. These operations preserve the
    value's identity as infinity or NaN (exponent all ones).
    The invalid operation exception is not raised when the destination
    is a non-empty stack element.


        Examples
        fst   [mem64]   ; store data, keep it on the top of the stack
        fstp  ST(0)     ; pop data off the top of stack, no data transfer
        fstp  ST(1)     ; pop ST(1), leaving ST(0) on the top of the stack
        fst   ST(4)     ; store ST(4)


    Opcode      Format
    D9 /2       FST m32
    DD /2       FST m64
    DD D0 + i   FST ST(i)
    D9 /3       FSTP m32
    DD /3       FSTP m64
    DB /7       FSTP m80
    DD D8 + i   FSTP ST(i)


    Timing
    Variations/
    operand       8087         287        387      486     Pentium
    fst  reg     15-22        15-22       11        3       1      NP
    fst  m32    (84-90)+EA    84-90       44        7       2      NP
    fst  m64    (96-104)+EA   96-104      45        8       2      NP
    fstp reg     17-24        17-24       12        3       1      NP
    fstp m32    (86-92)+EA    86-92       44        7       2      NP
    fstp m64    (98-106)+EA   98-106      45        8       2      NP
    fstp m80    (52-58)+EA    52-58       53        6       3      NP