condition (if a or b:) is always true

I have found that condition

  if (x == 0x08) or (x == 0x04):  # BUG is HERE!!
      seed += 1

is always true

When I rewrite that condition to two simpler conditions, it works OK.

  if x == 0x08:
      seed += 1
  elif x == 0x04:
      seed += 1

A bug demo, "monkey piano" has two versions of simple pseudo-random generators rnd1() and rnd2(). These functions differ in condition, function rnd1() is buggy and always sets the lowest bit (seed +=1). Function rnd2() works, it generates sequence of 15 numbers.

#-------------Setup----------------

import Ed

Ed.EdisonVersion = Ed.V2

Ed.DistanceUnits = Ed.CM
Ed.Tempo = Ed.TEMPO_MEDIUM

#--------Your code below-----------

def rnd1():
  global seed
  if seed == 0:
    seed = 1
  x = seed & 0x0c
  seed += seed
  if (x == 0x08) or (x == 0x04):  # BUG is HERE, condition is always TRUE
      seed += 1
  seed &= 0x0f
  return seed

def rnd2():
  global seed
  if seed == 0:
    seed = 1
  x = seed & 0x0c
  seed += seed
  if x == 0x08:
      seed += 1
  elif x == 0x04:
      seed += 1
  seed &= 0x0f
  return seed

def num2tone(x):
  duration = Ed.NOTE_QUARTER
  if x >= 8:
     duration = Ed.NOTE_HALF
  x %= 8
  if x == 0:
      t = Ed.NOTE_C_7
  elif x == 1:
      t = Ed.NOTE_D_7
  elif x == 2:
      t = Ed.NOTE_E_7
  elif x == 3:
      t = Ed.NOTE_F_7
  elif x == 4:
      t = Ed.NOTE_G_7
  elif x == 5:
      t = Ed.NOTE_A_7
  elif x == 6:
      t = Ed.NOTE_B_7
  elif x == 7:
      t = Ed.NOTE_C_8
  Ed.PlayTone(t, duration)
  while Ed.ReadMusicEnd() == Ed.MUSIC_NOT_FINISHED:
      pass

## MAIN()

seed = 1

while True:
    r = rnd1()  # function with a bug   #  0x03 0x07 0x0f 0x0f 0x0f 0x0f
    #r = rnd2()  # this works ok        #  0x02 0x04 0x09 0x03 0x06 0x0d
    Ed.SendIRData(seed)  
    Ed.TimeWait(100, Ed.TIME_MILLISECONDS)
    num2tone(r)

Demo for python at PC, it works:

def rnd():
  global seed
  if seed == 0:
    seed = 1
  x = seed & 0x0c
  seed += seed
  if (x == 0x08) or (x == 0x04):
      seed += 1
  seed &= 0x0f
  return seed

### MAIN()
seed = 1
for i in range(20):
   print rnd()

Simpler bug demo for Edison robot, just play with LEDs:

#-------------Setup----------------

import Ed

Ed.EdisonVersion = Ed.V2

Ed.DistanceUnits = Ed.CM
Ed.Tempo = Ed.TEMPO_MEDIUM

#--------Your code below-----------

# a=0 b=0 => OK
# a=0 b=1 => BUG (Left LED is not activated)
# a=1 b=0 => BUG (Left LED is not activated)
# a=1 b=1 => BUG (Left LED is not activated)

a = 0
b = 1

if (a==1) or (b==1):     # BUG is here, condition is always FALSE
    Ed.LeftLed(Ed.ON)

if (a==1):
    Ed.RightLed(Ed.ON)
elif (b==1):
    Ed.RightLed(Ed.ON)

while True:
    pass

and reference version for PC:

a = 0
b = 1

if (a==1) or (b==1):
    print "LEFT"

if (a==1):
    print "RIGHT"
elif (b==1):
    print "RIGHT"

Bdanilko / EdPy

condition (if a or b:) is always true #7