inc dec ,and carry flag

[ERNI]

Hey

are we know why INC  ,and DEC d't change CARRY flag ,but change ZERO and OVERLOF flags
WHY  :red :eek

[Mirno]

Because that is the design.
I'm sure it's more of a pain for Intel now, but the original x86 had those semantics, so they must continue with them.

Mirno

[raymond]

I have often found it very usefull that the CARRY flag was not affected by the INC/DEC instructions.

Simply use the SIGN flag if you need to be informed when a register gets decremented below 0 with the DEC instruction. That SIGN is also affected by the INC instruction.

Raymond

[tenkey]

Multiprecision arithmetic.

When incrementing addresses and decrementing loop counters, you don't want to destroy the carry/borrow between adds or subtracts.

[Mark Jones]

Look in Opcodes.HLP (possibly under JMP):
JC/JNC --> Jump if/not if Carry flag set
JS/JNS --> Jump if/not if Sign flag set