Shift Register Simulator with sound output

'Shift Register Simulator: Noise Generator with sound output
'(c)2021, @_sorceress

DEFLNG A-Z
DIM y AS SINGLE

'bitmasks for each tap
DIM SHARED Q(8): Q(1) = 1: FOR i = 2 TO 8: Q(i) = 2 * Q(i - 1): NEXT

SR1 = 1 'pre-load the first register

SampleRate = _SNDRATE 'generator frequency determined by soundcard

DO
  FOR i = 1 TO SampleRate

    'select an output tap
    y = Tap(SR3, 8)

    'output to soundcard * volume
    _SNDRAW y * 0.125

    'wiring the registers together
    SR1Data = Tap(SR3, 2) XOR Tap(SR3, 7) 'feedback
    SR2Data = Tap(SR1, 8) 'chaining SR1 and SR2
    SR3Data = Tap(SR2, 8) 'chaining SR2 and SR3

    'clock
    SR1 = (SR1 AND 127%) * 2 + SR1Data
    SR2 = (SR2 AND 127%) * 2 + SR2Data
    SR3 = (SR3 AND 127%) * 2 + SR3Data

  NEXT
  _LIMIT 1
LOOP UNTIL INKEY$ = CHR$(27) 'escape key halts the program
END

FUNCTION Tap (SR%, bit%)
  Tap = SGN(SR% AND Q(bit%))
END FUNCTION