How to learn assembely?

T.Jackson · - 6th May 2007, 12:18

Using Select Case is by far the very best methodology for implementing well structured decision making procedures. I'm a little uncertain as to just how advantageous it can be in PBP, but in Visual Basic, it's a god sent!

Consider the following:

Code:

SELECT CASE UserInput

   CASE 1
           GOSUB Temperature
           LOW LED
           
   CASE 2
           GOSUB LightLevel
           HIGH LED
END SELECT

<hr/>
Much easier to read and much faster. Select Case is a much more efficient, IF statement equivalent. However they can at times be a bit quirky for certain things.
<br/>

T.Jackson · - 6th May 2007, 13:34

Now consider the following:

Code:

      Select Case JoystickDat.dwXpos
             '//
             'right?
             '//
             Case Is > 50000
                  If Boat_ID <> 2 Then                               'sound on condition
                     If Master_SND_EN Then
                        If AllowRowSND = 0 And Jumping = False And Allow_SND_Effects = True Then
                           SND = sndPlaySound(App.Path & "\Water.wav", CSNDaSync)
                           AllowRowSND = 1                           'sound effect once only
                        End If                                       '
                     End If
                     '//                                             '
                     Rowing_Forward = True                           'set flag
                     Rowing_Backward = False                         'set flag
                     '//                                             '
                     If Jumping Then                                 '
                        'lmitied control when airborne               '
                        PlayerX = PlayerX + (PlayerX < 375) * -1     'inc 1 pixel
                        Boat_ID = 4                                 'ors out img
                     Else                                            '
                     'maintain screen limitations and inc boat forward
                        PlayerX = PlayerX + (PlayerX < 250) * -(1 + Row_Speed)
                        Row_Speed = Row_Speed + (Row_Speed < 20) * -2
                        Boat_ID = 2                                 'row img
                     End If
                     '//                                             '
                  Else                                               '
                     '//                                             '
                     If Jumping Then                                 '
                        Boat_ID = 4                                 'ors in img
                     Else                                            '
                        Boat_ID = 1                                 'ors out img
                     End If                                          '
                  End If
             '//
             'joystick center?
             '//
             Case Is > 500 And JoystickDat.dwXpos < 50000
                  If Jumping = False Then
                     If Master_SND_EN Then
                        If Row_Speed = 5 And Allow_SND_Effects = True Then
                           SND = sndPlaySound(App.Path & "\Water B.wav", CSNDaSync)
                        End If
                     End If
                  '//
                     Row_Speed = Row_Speed + (Row_Speed > 0) * 1     'grad dec speed                          '
                  '//                                                '
                     If Rowing_Forward Then                          '
                        Boat_ID = Boat_ID + (Boat_ID = 2) * 1     'reset image
                        Rowing_Forward = False                       'flag
                        AllowRowSND = 0                              'en sound for next time
                     Else                                            '
                        Boat_ID = Boat_ID + (Boat_ID = 0) * -1    'reset image
                        AllowRowSND = 0                              'en sound
                        Rowing_Backward = False                      'flag
                     End If
                  End If
             '//
             'left?
             '//
             Case Is < 500
                  If Boat_ID <> 0 Then                               'sound on condition
                     If Master_SND_EN Then
                        If AllowRowSND = 0 And Jumping = False And Allow_SND_Effects = True Then
                           SND = sndPlaySound(App.Path & "\Water.wav", CSNDaSync)
                           AllowRowSND = 1                           'en sound
                        End If                                       '
                     End If
                     '//
                     Rowing_Backward = True                          'set action flag
                     Rowing_Forward = False                          'set flag
                     '//                                             '
                     If Jumping = False Then                         '
                        PlayerX = PlayerX + (PlayerX > 50) * 10      'inc 10 pixel backward
                        Row_Speed = Row_Speed + (Row_Speed > 0) * 2  'grad dec speed                          '
                        Boat_ID = 0                                  'row back img
                     Else
                        'lmitied control when airborne               '
                        PlayerX = PlayerX + (PlayerX > 50) * 1       '
                        Boat_ID = 4                                  'ors out
                     End If
                     '//
                  Else
                     '//
                     If Jumping Then
                        Boat_ID = 4                                  'ors out img
                     Else                                            '
                        Boat_ID = 1                                  'ors in img
                     End If
                  End If
      End Select
      '//---//
      'Y-axis
      '//---//
      Select Case JoystickDat.dwYpos
             '//
             'up?
             '//
             Case Is < 500
                  If Jumping Then
                     PlayerY = PlayerY + (PlayerY > 375) * 2         'inc 2
                  Else
                     PlayerY = PlayerY + (PlayerY > 375) * 5         'inc 5
                  End If
             '//
             'down
             '//
             Case Is > 50000
                  If Jumping Then
                     PlayerY = PlayerY + (PlayerY < 475) * -2        'inc 2 pixel
                  Else                                               '
                     PlayerY = PlayerY + (PlayerY < 475) * -5        'inc 5
                  End If
      End Select

<hr/>
Now, while Select Case itself isn't used for all decision making, its main role here is for structure. It greatly improves clarity and organization. It clearly separates the algorithm into much more easily manageable parts. It's perhaps not quite that obvious in this example because there's really on 2 parts in each Select Case.
<br/>

T.Jackson · - 6th May 2007, 13:44

Last example:

Code:

   Select Case X
          
          Case 5 To 20
               Col_Loc = 0
               Cur_PosX = 5
               Str_Day = "Sunday"
          
          Case 28 To 43
               Col_Loc = 1
               Cur_PosX = 28
               Str_Day = "Monday"
          
          Case 51 To 66
               Col_Loc = 2
               Cur_PosX = 51
               Str_Day = "Tuesday"
          
          Case 74 To 89
               Col_Loc = 3
               Cur_PosX = 74
               Str_Day = "Wednesday"
    
          Case 97 To 112
               Col_Loc = 4
               Cur_PosX = 97
               Str_Day = "Thursday"
               
          Case 120 To 135
               Col_Loc = 5
               Cur_PosX = 120
               Str_Day = "Friday"
    
          Case 143 To 166
               Col_Loc = 6
               Cur_PosX = 143
               Str_Day = "Saturday"
   End Select

Procedure taken from a calendar program that I made few months back relies totally on Select Case to do the job. Extremely tidy & extremely fast!
<br/>

**mister_e** · - 6th May 2007, 13:35

</td><td>It wasn't meant to be a 'how to create efficient code' tutorial or contest, but just an example.

Who i'm i anyway ?</td></tr></table>

FYI, in PBP Select Case will be a little less code efficient (talking about code size) than multiple IF-THEN-ELSE... as with ALL other language anyway. Select Case is just easier to read, modify, implement. Save your finger nails...

We are really far of the original question...

T.Jackson · - 6th May 2007, 13:48

Originally Posted by mister_e

FYI, in PBP Select Case will be a little less code efficient (talking about code size) than multiple IF-THEN-ELSE... as with ALL other language anyway. Select Case is just easier to read, modify, implement. Save your finger nails...

Try making a Nintendo Emulator in VB using IF's as opposed to Select Case. There's about a %25 difference in speed.

Code:

   Select Case instruction(opcode)
          Case INS_JMP: ' jmp6502
               adrmode opcode
               PC = savepc
           Case INS_LDA: ' lda6502
               adrmode opcode
               a = Read6502(savepc)
               SetFlags a
           Case INS_LDX:
               adrmode (opcode)
               x = Read6502(savepc)
               SetFlags x
           Case INS_LDY
               adrmode (opcode)
               y = Read6502(savepc)
               SetFlags y
           Case INS_BNE: bne6502
           Case INS_CMP: cmp6502
           Case INS_STA
               adrmode (opcode)
               Write6502 savepc, a
           Case INS_BIT: bit6502
           Case INS_BVC: bvc6502
           Case INS_BEQ: beq6502
           Case INS_INY: iny6502
           Case INS_BPL: bpl6502
           Case INS_DEX: dex6502
           Case INS_INC: inc6502
           Case INS_DEC: dec6502
           Case INS_JSR: jsr6502
           Case INS_AND: and6502
           Case INS_NOP:
    
           Case INS_BRK: brk6502
           Case INS_ADC: adc6502
           Case INS_EOR: eor6502
           Case INS_ASL: asl6502
           Case INS_ASLA: asla6502
           Case INS_BCC: bcc6502
           Case INS_BCS: bcs6502
           Case INS_BMI: bmi6502
           Case INS_BVS: bvs6502
           Case INS_CLC: p = p And &HFE
           Case INS_CLD: p = p And &HF7
           Case INS_CLI: p = p And &HFB
           Case INS_CLV: p = p And &HBF
           Case INS_CPX: cpx6502
           Case INS_CPY: cpy6502
           Case INS_DEA: dea6502
           Case INS_DEY: dey6502
           Case INS_INA: ina6502
           Case INS_INX: inx6502
           Case INS_LSR: lsr6502
           Case INS_LSRA: lsra6502
           Case INS_ORA
                adrmode opcode
                a = a Or Read6502(savepc)
                SetFlags a
    
           Case INS_PHA: pha6502
           Case INS_PHX: phx6502
           Case INS_PHP: php6502
           Case INS_PHY: phy6502
           Case INS_PLA: pla6502
           Case INS_PLP: plp6502
           Case INS_PLX: plx6502
           Case INS_PLY: ply6502
           Case INS_ROL: rol6502
           Case INS_ROLA: rola6502
           Case INS_ROR: ror6502
           Case INS_RORA: rora6502
           Case INS_RTI: rti6502
           Case INS_RTS: rts6502
           Case INS_SBC: sbc6502
           Case INS_SEC: p = p Or &H1
           Case INS_SED: p = p Or &H8
           Case INS_SEI: p = p Or &H4
           Case INS_STX
                adrmode (opcode)
                Write6502 savepc, x
           
           Case INS_STY
                adrmode (opcode)
                Write6502 savepc, y
           Case INS_TAX: tax6502
           Case INS_TAY: tay6502
           Case INS_TXA: txa6502
           Case INS_TYA: tya6502
           Case INS_TXS: txs6502
           Case INS_TSX: tsx6502
           Case INS_BRA: bra6502
      End Select

(This procedure is not my code, but I wish it was)

T.Jackson · - 6th May 2007, 14:35

Main reason why Select Case is faster than using multiple IF's is because not all conditions are checked, only the first true condition in a Select Case argument has its underlying block of code executed.

That's my theory on it anyway.

**mister_e** · - 6th May 2007, 14:51

unless your using a little bit of your brain, it's true.

Code:

plah plah plah
Avar=Whatever
Gosub StartSelectCase
plah
plah
plah
'
'
'

StartSelectCase:
    If AVar=1 then
        Dosomething
        Return
        Endif

    If AVar=2 then
        Dosomething
        Return
        Endif
    '
    '
    '
    If AVar=x then
        Dosomething
        Endif

    Return

V2

Code:

AVar = Whatever

StartSelectCase:
    If AVar=1 then
        Dosomething
        Goto EndSelectCase
        Endif

    If AVar=x then
        Dosomething
        Goto EndSelectCase
        Endif
    '
    '
    '
    If AVar=y then
        Dosomething
        Endif
EndSelectCase:

Sort of what's under the SelectCase hood.

Now depending how the compiler, language interpret/optimise it, one can be faster than the other. It's hard to tell which will ALWAYS be faster so far as there's millions (and more) different possible itteration/conditions.

Both get the job done! One is easier to read, implement debug.

T.Jackson · - 7th May 2007, 02:48

Pretty sure you'll find that for every IF argument, unlike Select Case, the subject variable to compare with is loaded into a working register each time.
However with Select Case it's already there for the next compare. Possibly the closed analogy of Select Case would be ELSEIF. But it's no where near as flexible unfortunately.
<br/>

**mister_e** · - 26th May 2007, 21:23

Back to the original topic. Here's an interesting MicroChip on-line flash tutorial.

http://techtrain.microchip.com/x14/

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Select Case - By far the best way!

Slightly more complex Select Case example

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i knew this was going to happen...

Reason why Select Case is faster!

I think there's other diferences too.

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