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Testing Inline ASM-VB
Strings
Math
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Using inline ASM
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Testing Inline ASM-VB
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Using inline ASM
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Bitshifting with inline ASMWith bitshifting you can shift bits left or right, effectively multiplying or dividing the number by two.
It's a standard processor operation, and it's quite a common use in C which supports it standardly.
This small piece of code will allow you to do bit shifting (both left and right) easily.
A VB version is also included.
User contributed notes:
It's a standard processor operation, and it's quite a common use in C which supports it standardly.
This small piece of code will allow you to do bit shifting (both left and right) easily.
A VB version is also included.
Public Function asmBitShiftLeft(ByVal Number As Long, ByVal Shift As Long) As Long '#ASM_START ' push ebp ' mov ebp, esp ' ' mov eax, [ebp+8] ; Get first argument ' mov ecx, [ebp+12] ; Get second argument ' shl eax, cl ' mov esp, ebp ;MOV/POP is much faster ' pop ebp ;on 486 and Pentium than Leave ' ret 8 '#ASM_END End Function Public Function asmBitShiftRight(ByVal Number As Long, ByVal Shift As Long) As Long '#ASM_START ' push ebp ' mov ebp, esp ' ' mov eax, [ebp+8] ; Get first argument ' mov ecx, [ebp+12] ; Get second argument ' shr eax, cl ' mov esp, ebp ;MOV/POP is much faster ' pop ebp ;on 486 and Pentium than Leave ' ret 8 '#ASM_END End Function Public Function vbBitShiftLeft(ByVal Number As Long, ByVal Shift As Long) As Long Dim I As Long vbBitShiftLeft = Number For I = 1 To Shift vbBitShiftLeft = vbBitShiftLeft * 2 Next I End Function Public Function vbBitShiftRight(ByVal Number As Long, ByVal Shift As Long) As Long Dim I As Long vbBitShiftRight = Number For I = 1 To Shift vbBitShiftRight = vbBitShiftRight / 2 Next I End Function |
| VBBitShift % faster than ASMBitShift | VBBitShift (sec) | ASMBitShift (sec) |
| 98.1% | 0.000267 | 0.000135 |
| 100% | 0.00027 | 0.000135 |
| 96.3% | 0.000265 | 0.000135 |
| 96.3% | 0.000265 | 0.000135 |
| 100% | 0.000268 | 0.000134 |
| VBBitShift % faster than ASMBitShift | VBBitShift (sec) | ASMBitShift (sec) |
| 76% | 0.000547 | 0.000311 |
| 61.9% | 0.000546 | 0.000337 |
| 78.8% | 0.000546 | 0.000305 |
| 108% | 0.000634 | 0.000305 |
| 490.5% | 0.001831 | 0.00031 |
User contributed notes:
| Author: Tom (hurendo_kun at hotmail dot com) | Date: 16:06 08/06/2005 |
|
Just a reminder: bit-shifting only works on integers. If you need to shift a float, you can type-cast it --- visit GameDev and search the forums for "Carmack Inverse Square Root" to find out why. |
|
| Author: Randomguy () | Date: 10:12 18/12/2005 |
| Uh, is it just me or shouldn't you have just divided once by 2^shift? (calculate that beforehand tho) | |
| Author: Spodi () | Date: 05:04 15/04/2007 |
| And shouldn't the division be integer-divison, not floating-point division? As your other test on that shows, that makes a significant difference. ;) | |
| Author: Almar () | Date: 19:04 15/04/2007 |
| Both correct. :). | |