Fast Bit Check (Inline Assembly)
First off, credits go to a friend...
Using the following:
http://thundervb.profitux.cz/go.php?adr=home
VB Code:
'Note double dereference because passing byref
Public Function CheckBits(lngNumber As Long, lngTest As Long) As Boolean
'#asm' mov eax,[esp+4] ;Move pointer to lngNumber into eax
'#asm' mov eax,[eax] ;Move value of lngNumber into eax
'#asm' mov ecx,[esp+8]
'#asm' mov ecx,[ecx]
'#asm' not eax
'#asm' test eax,ecx ;And the value of lngNumber with lngTest and effect SF, ZF, and PF
'#asm' .IF !ZERO? ;Is the zero flag not set (bit set)
'#asm' xor eax,eax ;Return false
'#asm' .ELSE
'#asm' mov eax,-1 ;Return true
'#asm' .ENDIF
'#asm' ret 8
End Function
However, he had to write a second one for those cases where Visual Basic's signed long can't hold a mask capable of checking every bit in an unsigned long. Work with file formats, you will understand why you need the speed of assembly and unsigned longs .
VB Code:
Public Function CheckBitNumber(lngNumber As Long, lngBitNumber As Long) As Boolean
'#asm' mov ecx,[esp+8] ;Calculate 2^(lngBitNumber - 1) and place it in eax
'#asm' mov cl,[ecx]
'#asm' dec cl
'#asm' mov eax,1
'#asm' shl eax,cl
'#asm' mov ecx,[esp+4] ;Move pointer to lngNumber into ecx
'#asm' mov ecx,[ecx] ;Move value of lngNumber into ecx
'#asm' test eax,ecx ;And the value of lngNumber with lngTest and effect SF, ZF, and PF
'#asm' .IF ZERO? ;Is the zero flag set (bit not set)
'#asm' xor eax,eax ;Return false
'#asm' .ELSE
'#asm' mov eax,-1 ;Return true
'#asm' .ENDIF
'#asm' ret 8
End Function
Enjoy :)
Re: Fast Bit Check (Inline Assembly)
Re: Fast Bit Check (Inline Assembly)
Quote:
Originally Posted by Hack
Moved from CodeBank VB6
However, it is indeed visual basic, its just using inline asm :) Just thought I'd let you know.
