**Next message:**Gary Barnett: "RE: [Circle] [CIRCLE] Limits on classes?"**Previous message:**Rasdan: "[Circle] [CIRCLE] Limits on classes?"**Maybe in reply to:**DJ Pure: "[Circle] Bitvector Explanation please"**Next in thread:**Christopher M. Ryan: "Re: [Circle] Bitvector Explanation please"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

At 10:06 AM 11/29/96 +1100, you wrote: >G'Day All, > i've read the docs, but i'm still unfamiliar with bitvectors and what >they do. i know how to impleement them, but I'm not sure how to use them in >the game. >For example. I had this >#define open 0 >#define closed 1 >#define locked 2 >#define pickproof 3 >#define secret_closed 4 >#define secret_locked 5 >#define secret_pickproof 6 > >and i was told i don't nned 5 and 6 cause 4 already 'encompasses' them. >This is why I'm confussed, so can someone quickly explain them please >*blush* > >Thanks as always. i don't knwo if this explanation is neccessary seeing as how someone else already responded.. but i felt his explanation wasn't in plain english as much as i would like if i knew nothing about bitvectors.. so here it goes for what it's worth.. as you know the computer stores information in 1's and 0's.. A single bit is either a 1 or a 0.. to store a bigger number the computer uses a series of 1's and 0's (several bits).. this is known as binary. it goes something like this.. 0=0000 1=0001 2=0010 3=0011 4=0100 5=0101 6=0110 7=0111 8=1000 9=1001 10=1010 11=1011 12=1100 13=1101 14=1110 15=1111 and so on.. my demonstration here shows only a 4 bit number.. typically in your computer an integer on most platforms these days is 32 bits (so an integer of 1 would be stored as 00000000000000000000000000000001).. now that we have that down lets continue. when people refer to bitwise operations they are talking about changing those bits in some way.. its a little abstract i guess. there are only a few bit operations you can do.. you can shift left, shift right, or compliment the bits. for example. in the code you often see (1 << 0) or (1 << 1) or (1 << 2).. what is this crap you ask? the "<<" is a shift left operation on the bits.. when you say 1 << 0 you are saying to take the number 1 and shift the bits to the left 0 spaces. So if you had the number 1 you would have 0001 and doing the shift left 0 operation you would still have 0001. If you did a (1 << 1) you are shifting the bits left once.. thus 0001 would turn into 0010.. if you look at the above table i wrote out a 0010 is actually equal to 2. if you do a (1 << 2) you are shifting the bit left twice so a 0001 turns into a 0100 which is equal to 4. thus if you have an integer variable stored as 1 and you shift it, you are changing the value of the integer value depending on how you shift it. Right shifting is the exact opposite.. like (4 >> 1) would turn 0100 into 0010 because we are shifting the bits in the number 4 right one space. ok so how does this apply to what you are asking above? simple.. take a look at your list here: >#define open 0 >#define closed 1 >#define locked 2 >#define pickproof 3 >#define secret_closed 4 >#define secret_locked 5 >#define secret_pickproof 6 you are defining the above words to this: open = 0000 closed = 0001 locked = 0010 pickpr = 0011 ETC.. if you look at the individual bits.. the first bit furthest to the right is used to determine if the door is open or closed. if it's open the furthest bit to the right is a 0.. if it's closed the furthest bit is a 1.. thats how you tell if the door is opened or close. the program checks the status of that bit in the integer to determine the status of the door.. the second bit from the right is used to determine if the door is locked or not. so you could have the following combinations.. 0000 = door open and unlocked 0001 = door closed and unlocked 0010 = door open and locked (impossible to occur.. the program should never assign it this) 0011 = door closed and locked you should notice that your last four pose a problem. if you want to make something pickproof you need to assign another bit for that.. so when defining pickproof you need to define it 4, not 3.. because 4 would be 0100 and thuse you'd be using the third bit in to determine if the door is pickproof or not. i would think you're looking to do more something like this.. 0000 = open 0001 = closed 0010 = locked 0100 = pickproof 1000 = secret notice the position of the 1 bit.. the right one determines if the door is open or closed.. second one in determines if it's locked.. third one in determines if it's pick-able.. and the forth determines if its secret. thus you can have any combination of the above to create any situation.. if you wanted a closed secret door that is locked and pickproof the value of the door would be: 1111 am i making sense here? i hope so.. if you go back up and look at your defines you will see that the way you're assigning them does not only not make sense but you should also see what the later combinations are not neccessary. and why bitvectors are used in this fation.. thats where the power lies in them. excuse my spelling as it is late :) -Gerald +-----------------------------------------------------------+ | Ensure that you have read the CircleMUD Mailing List FAQ: | | http://cspo.queensu.ca/~fletcher/Circle/list_faq.html | +-----------------------------------------------------------+

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