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(nasm.info)Section B.4.191

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B.4.191. `OR': Bitwise OR
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     OR r/m8,reg8                  ; 08 /r                [8086]
     OR r/m16,reg16                ; o16 09 /r            [8086]
     OR r/m32,reg32                ; o32 09 /r            [386]

     OR reg8,r/m8                  ; 0A /r                [8086]
     OR reg16,r/m16                ; o16 0B /r            [8086]
     OR reg32,r/m32                ; o32 0B /r            [386]

     OR r/m8,imm8                  ; 80 /1 ib             [8086]
     OR r/m16,imm16                ; o16 81 /1 iw         [8086]
     OR r/m32,imm32                ; o32 81 /1 id         [386]

     OR r/m16,imm8                 ; o16 83 /1 ib         [8086]
     OR r/m32,imm8                 ; o32 83 /1 ib         [386]

     OR AL,imm8                    ; 0C ib                [8086]
     OR AX,imm16                   ; o16 0D iw            [8086]
     OR EAX,imm32                  ; o32 0D id            [386]

   `OR' performs a bitwise OR operation between its two operands (i.e.
each bit of the result is 1 if and only if at least one of the
corresponding bits of the two inputs was 1), and stores the result in
the destination (first) operand.

   In the forms with an 8-bit immediate second operand and a longer
first operand, the second operand is considered to be signed, and is
sign- extended to the length of the first operand. In these cases, the
`BYTE' qualifier is necessary to force NASM to generate this form of
the instruction.

   The MMX instruction `POR' (see *Note Section B.4.247::) performs the
same operation on the 64-bit MMX registers.