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set bit using C Action Script

Created by: P.C. at: 3/24/2009 6:28 AM (6 Replies)

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3/24/2009 6:28 AM	Rate (0)
P.C. Posts: 23 Rating: (1)	Hey guys I posted a thread a month ago regarding to bitwise AND & bitwise OR in C action script. I got a lot of help from y'all at that time. I want to thank y'allagain. I just came up another question recently and I hope you guys wouldn't mind to give me some hints again. The script is like this: define TAG_0 "SAMPLE" DWORD dwHelp1,dwHelp2; dwHelp1=GetTagDWordWait(TAG_0); dwHelp2=dwHelp1\|-524288; SetTagDWordWait(TAG_0,dwHelp2); What I do not understand is the minus sign in front of 524288. If the line was dwHelp2=dwHelp1\|524288 intead, I would know it simply meansSET bit 19 of tag SAMPLE. But I really don't know what the minus sign do here. Do you guysknow what it means? Thank you all. P.C.
P.C. Posts: 23 Rating: (1)
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3/24/2009 4:08 PM	Rate (0)
Tolleif Experienced Member Joined: 9/7/2005 Last visit: 11/7/2023 Posts: 31 Rating: (9)	The code is difficult to read. What is the intention with the OR? First,avoid writing numbers asdecimal values when you're manipulating bits, hexadecimal is much easier. 524288 = 0x80000 dwHelp2=dwHelp \| 0x80000; would force BIT 19 and leave the rest untouched. if you use 2's complement ( negative number ) you will invert the 0x80000 to FFF80000. ORing with this number may or may not be what you want to do.... Tolleif
	Siemens Oil&Gas Offshore Norway
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3/25/2009 10:10 AM	Rate (0)
P.C. Posts: 23 Rating: (1)	Thx. I will avoid using negative number.
P.C. Posts: 23 Rating: (1)
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3/25/2009 5:09 PM	Rate (0)
CBo Gold Member Joined: 4/5/2006 Last visit: 11/28/2024 Posts: 917 Rating: (63)	Hi P.C., Tolleifis right, better use Hex mask, more easier to understood and maintenance. One more, that code works on "Unsigned 32 bits" WinCC tags, when you ry to use that code using decimal negative number mask on "Signed 32 bits" WinCC tags...nothing happens. So, have a look what tags format are you using. Regards

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3/26/2009 12:47 PM	Rate (0)
P.C. Posts: 23 Rating: (1)	Hey guys, Thank you for your replies. I just found out if the code was changed to dwHelp2=dwHelp1&(0xFFFFFFFF^524288); It would reset bit 19 and I tested already. I am trying to understand the principle behind it. What does "^" symboldo here? I guess I will read y'all replies again and see if I can figure out. Best wishes, P.C.
P.C. Posts: 23 Rating: (1)
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3/30/2009 7:48 AM	Rate (0)
uel123 Gold Member Joined: 1/29/2006 Last visit: 11/30/2024 Posts: 447 Rating: (64)	P.C. ... dwHelp2=dwHelp1&(0xFFFFFFFF^524288); It would reset bit 19 ... Hi! Operator "^" is for bitwise XOR operation. Let see, what your code does (step by step): Firststep(0xFFFFFFFF^524288): Due to reasons of clarity, I would rather write this in HEX notation, as you were allready advised from other users: (0xFFFFFFFF^0x00080000): The result of this operation is 0xFFF7FFFF (bit 19 isset to 0, all other are 1). Or in other words, bit 19 from first operand is TOGGLED! XOR means "EXCLUSIVE OR": Table for (bitwise) XOR operation: bit0 bit1 RESULT 0 0 XOR = 0 1 0 XOR = 1 0 1 XOR = 1 1 1 XOR = 0 XOR is normally used to TOGGLE bits from first operand. The position of bit, which has to be toggled in first operand, is defined with position of "1" in second operand (=some sort of mask!). Second step: dwHelp1&(Result_of_first_step) = dwHelp1&(0xFFF7FFFF): The result of this operation is than really resetting of bit 19...... have fun! uel123

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3/31/2009 4:47 AM	Rate (0)
P.C. Posts: 23 Rating: (1)	Thanks! Very helpfuland detailed explanation.
P.C. Posts: 23 Rating: (1)
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