Signed long to Unsigned long..

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Hi All,

can you please let me know how can I get unsigned long equivalent to signed long value??? i do not want code,i need formula.

Example: if signed long var = -15 then what will be equivalent value of var when it is unsigned?

Please reply.
Please note that i am not looking for code,i need formula only.

Posted 23-Aug-12 1:50am

joyjhonson

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3 solutions

Solution 1

If you look here[^], climits.h contains the limits of types for your implimentation of C++ ( although it should not change ). I believe a signed number uses the highest bit to specific the sign. So, if you reverse the sign and add (ULONG_MAX - LONG_MAX), to get the value of the high bit in an unsigned long, I think that's your answer.

Posted 23-Aug-12 2:08am

Christian Graus

Solution 2

In C++ a signed long containing -15 is hex 0xFFFFFFF1. Copying that to an unsigned long gives the same hex value which is 4294967281 decimal. There is no formula for this, in code you just use the same value but ignore the sign bit and treat it as positive.

Posted 23-Aug-12 2:13am

Richard MacCutchan

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nv3 · Accepted Answer · 2012-08-23T02:23:00

Solution 3

Most processors nowadays work with 2's complement representation. That means that to build the negative value of a number n the formula

nneg = (2**WordSize - n) mod 2**WordSize

is used. For a 32-bit processor and your example value 15 that would be

nneg = 2**32 - 15 = 4 294 967 281 = 0xFFFF FFF1

Some older processors use One's Complement representation. For them the formula is

nneg = (2**WordSize-1 - n) mod 2**WordSize

which means that the value 0 has two representations namily 0x00000000 and 0xffffffff.

Posted 23-Aug-12 2:23am

nv3

Comments

pasztorpisti 23-Aug-12 10:00am

+5, additional info: http://en.wikipedia.org/wiki/Two%27s_complement

nv3 23-Aug-12 10:02am

Thanks!

JackDingler 23-Aug-12 10:59am

Good answer. My 5

nv3 23-Aug-12 11:08am

Thanks, Jack!