Arm Development Studio forum Carry-Bit vs. Documentation

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Carry-Bit vs. Documentation

Note: This was originally posted on 27th June 2012 at http://forums.arm.com

Hello,

in every documentation I found something like

"A carry occurs (..), if the result of a subtraction is positive, (...)."

If I understand this right after a substraction (this is important) with a negativ (N = 1) result there can´t occur a carry, isn´t it?

For examble if I try

0x7FFF FFFF - 0xFFFF FFFF = 0x8000 0000
The CPSR are set like this NzcVqIFt_SVC => N = 1, C = 0, V = 1

After a substraction - Carry (borrow) = 0 means we have a borrow! Right?
So a carry occurs but the result is negativ!

Is the documentation right and complete? Or is there something missing or I´m completely wrong?

Thanks
RenÃ©