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Binary operations

Started by Velochy Jul 22, 2002 at 2:17 AM 3 replies 200+ views

Original Post

Jul 22, 2002 at 2:17 AM

one question.. say a=10101101 and b=1010 would a & b return 10101000 or just 1000 ? also whats the use of these:

  
for(INT i = 0; i < 8; i++)
{
	dist = (i & 0x4) ? FAR_CLIP : NEAR_CLIP;
	t = (i & 0x2) ? t : -t;
	t = (i & 0x1) ? -t : t;
}

I am thinking the first would return true if number>=0 and false otherwise but i cant seem to figure out what the 2 others do

Gee

Jul 22, 2002 at 2:39 AM

My question is how you declair b (the nibble) in C++ ?

And btw it will be 1000...

Velochy

Jul 22, 2002 at 2:48 AM

i dont

they are just for this forum for arguments sake

Monder

Jul 22, 2002 at 5:03 AM

You can''t declare a nibble because memory is addressed by the byte so the smallest thing you can declare is a byte(unsigned char in c/c++)

LessBread

Jul 22, 2002 at 5:48 AM

quote:
Original post by Velochy

for(INT i = 0; i < 8; i++)
{
dist = (i & 0x4) ? FAR_CLIP : NEAR_CLIP;
t = (i & 0x2) ? t : -t;
t = (i & 0x1) ? -t : t;
}

I am thinking the first would return true if number>=0 and false otherwise but i cant seem to figure out what the 2 others do

The first returns true if i >= 4 in the range 0-7. Examine the bit patterns below.

The result of the other two depend on t being predefined, in which case the sign is fliped accordingly, but watch the fall through.


        & 0x2    & 0x1    t(n) 
0:0000  F  -t   F  t      -t
1:0001  F  -t   T  -t     t
2:0010  T  t    F  t      t
3:0011  T  t    T  -t     -t
4:0100  F  -t   F  t      -t
5:0101  F  -t   T  -t     t 
6:0110  T  t    F  t      t
7:0111  T  t    T  -t     -t
8:1000

[edited by - lessbread on July 22, 2002 6:51:07 AM]

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