Converting Two's Complement from Hex to Decimal

[joatmon]

I don't understand how to do this. I understand how to convert from Hex to Decimal, but not specifically with Two's Complement form. I need to convert 0xfffffe58 into decimal form. I get that the first character here indicates that the number is negative, and I know that the decimal equivalent is -424. I tried these approaches:

-15 * 16^7 + 15*(16^6 + 16^5 + 16^4 + 16^3) + 14*16^2 + 5*16 + 8

and

-15*16^3 + 14*16^2 + 5*16 + 8

I also thought that it might be correct to just do this:

(14*16^2 + 5*16 + 8 + 1) * -1

None of these are right, and I can't find out how to do this anywhere. Can anybody help? Thanks!

[tabstop]

Subtract 0xfffffe58 from 0xffffffff to get 0x000001a7, also known as 423, then add 1 and tack the minus sign on.

(EDIT: Or I suppose you can do it the "proper" way, which is to subtract 0x100000000, since that is what the word "two's complement" means, to take it away from a power of two.)

[quzah]

You should probably start here: Two's complement - Wikipedia, the free encyclopedia


Quzah.

[itCbitC]

Subtract 1 from the hex number and take its 1's complement.
But as noted, it's vital to understand 2's complement notation.