asr

Sizes

byte, word, long

Default Size

word

Affected Flags

✱

Operands

Op 1

Dn/Im

Op 2

Shifts the bits of the destination operand to the "Right". Two forms: (1) as<d> Dx/Im, Dn shifts Dn by the count in Dx or immediate (1–8), any size. New bits are filled with the sign bit. Defaults to word. Note: ASL sets the overflow flag if the MSB changes during the shift, while ASR always clears it. (2) as<d>.w (An) shifts a memory word by 1; .w is the only size accepted and may be omitted.

* --- ASR: arithmetic shift right (preserves sign) ---
move.w #$FF00, d0
asr.w #4, d0 ; d0 = $FFF0 (sign bit preserved)

move.w #$0F00, d1
asr.w #4, d1 ; d1 = $00F0 (positive, fills with 0)

* --- ASL: arithmetic shift left ---
move.w #$0001, d2
asl.w #4, d2 ; d2 = $0010

; ASL sets V if the MSB changes during the shift
move.w #$7000, d3
asl.w #1, d3 ; V flag set! MSB changed from 0 to 1

* --- Memory form: shifts word at (a0) left by 1 ---
lea $1000, a0
move.w #$0001, (a0)
asl (a0) ; (a0) = $00021
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