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(nasm.info)Section B.4.142

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B.4.142. `LOOP', `LOOPE', `LOOPZ', `LOOPNE', `LOOPNZ': Loop with Counter
------------------------------------------------------------------------

     LOOP imm                      ; E2 rb                [8086]
     LOOP imm,CX                   ; a16 E2 rb            [8086]
     LOOP imm,ECX                  ; a32 E2 rb            [386]

     LOOPE imm                     ; E1 rb                [8086]
     LOOPE imm,CX                  ; a16 E1 rb            [8086]
     LOOPE imm,ECX                 ; a32 E1 rb            [386]
     LOOPZ imm                     ; E1 rb                [8086]
     LOOPZ imm,CX                  ; a16 E1 rb            [8086]
     LOOPZ imm,ECX                 ; a32 E1 rb            [386]

     LOOPNE imm                    ; E0 rb                [8086]
     LOOPNE imm,CX                 ; a16 E0 rb            [8086]
     LOOPNE imm,ECX                ; a32 E0 rb            [386]
     LOOPNZ imm                    ; E0 rb                [8086]
     LOOPNZ imm,CX                 ; a16 E0 rb            [8086]
     LOOPNZ imm,ECX                ; a32 E0 rb            [386]

   `LOOP' decrements its counter register (either `CX' or `ECX' - if
one is not specified explicitly, the `BITS' setting dictates which is
used) by one, and if the counter does not become zero as a result of
this operation, it jumps to the given label. The jump has a range of 128
bytes.

   `LOOPE' (or its synonym `LOOPZ') adds the additional condition that
it only jumps if the counter is nonzero _and_ the zero flag is set.
Similarly, `LOOPNE' (and `LOOPNZ') jumps only if the counter is nonzero
and the zero flag is clear.