32-bit signed int to 16-bit unsigned int

[dantheman]

anybody can tel me y

Int32 supervar = 1151;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 1149

same for

Int32 supervar = 21319;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 21317;

thank for any tips

[Rick Lones]

dantheman wrote:

anybody can tel me y

Int32 supervar = 1151;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 1149
Your mask constant of 0xFFFD in binary is 0b1111111111111101. Any value of
supervar that you logically AND with this mask will pass through unchanged
except that if the next-to-low-order bit is a one it will be changed to a zero.

Arithmetically interpreted, this is equivalent to subtracting 2 from supervar if
supervar mod 4 is either 2 or 3.

In your case at hand, 1151 decimal is 0x47F - it becomes 0x47D after masking
(ANDing5345), which is indeed 1149 decimal.
same for
Int32 supervar = 21319;

Yes, the same. 0x5347 becomes 0x5345 after the AND operation.

HTH,
-rick-

[dantheman]

thanks rick

so if get this
if supervar mod 4 is either 2 or 3 i should add 2 so i will get the
poper answer of 1151 and 21319

thank you very much i appreciate it

[Dan Neely]

"dantheman" wrote:

anybody can tel me y

Int32 supervar = 1151;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 1149
1151 = 0000 0100 0111 1111 binary. FFFD = 1111 1111 1111 1101 binary.

0000 0100 0111 1111
1111 1111 1111 1101 &
0000 0100 0111 1101 = 1149
same for

Int32 supervar = 21319;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 21317;

21317 = 0101 0011 0100 0111 binary. The same thing happens as before, by
anding with FFFD you're setting the 2 bit to zero, and since the number
you're anding with had it set to 1 you're subtracting two from it.

[Jon Skeet [C# MVP]]

dantheman <da******@hotmail.com> wrote:

thanks rick

so if get this
if supervar mod 4 is either 2 or 3 i should add 2 so i will get the
poper answer of 1151 and 21319

thank you very much i appreciate it

It's not entirely clear what "proper answer" you're after. If you're
just trying to mask off sixteen bits, just use 0xffff instead of
0xfffd. Alternatively, use a ushort:

ushort converted = (ushort) supervar;

However, you need to decide what you want to happen if supervar is
negative.

--
Jon Skeet - <sk***@pobox.com>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Rick Lones]

dantheman wrote:

thanks rick

so if get this
if supervar mod 4 is either 2 or 3 i should add 2 so i will get the
poper answer of 1151 and 21319

thank you very much i appreciate it

Well . . . what he (Jon) said. The "proper answer" depends on what the actual
problem is. I only mentioned an "arithmetic interpretation" because you framed
your original question in terms of integer results. Really it's a logical AND
operation being performed bitwise on a bunch of adjacent bits, that's all.
Normally, with a mask such as 0xFFFD the "natural" assumption would be that the
point of the AND operation is to force a particular bit to zero while leaving
all the others unchanged, rather than to perform some exotic arithmetic trick.

Your comment above about adding 2 seems to be about how to reverse the AND
operation. The more natural way to do that would be to perform a logical OR
with the inverse of your mask. In this case, OR'ing with 0x0002 would be the
logical inverse of AND'ing with 0xFFFD.

-rick-

[Stoitcho Goutsev \(100\)]

dantheman,

What do you expect the result to be?

1151(decimal) = 0000010001111111 (binary)
FFFD(hex) = 1111111111111101 (binary)

When we perform the bitwise AND operation the result ould be
0000010001111111
1111111111111101
------------------------
0000010001111101

0000010001111101 (binary) = 1149 (decimal)

This is exaclty the result you get.

The same for the other numbers.
--
HTH
Stoitcho Goutsev (100)

"dantheman" <da******@hotmail.com> wrote in message
news:11*********************@v46g2000cwv.googlegro ups.com...

anybody can tel me y

Int32 supervar = 1151;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 1149

same for

Int32 supervar = 21319;

but when i do
supervar = supervar & 0xFFFD;

supervar becomes = to 21317;

thank for any tips

[dantheman]

hi guys,

sorry for not being realy clear on this "it was a long day..."
that's exacly what i was trying to do is to "mask off sixteen bits from
the final result" so i used 0xffff instead of 0xfffd and it all works
like it should so fare...

thank you for your help