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Intel Pentium CPU Instruction Set Reference

INC instruction - Increment by 1

Code Mnemonic Description
FE /0 INC r/m8 Increment r/m byte by 1
FF /0 INC r/m16 Increment r/m word by 1
FF /0 INC r/m32 Increment r/m doubleword by 1
40 + rw INC r16 Increment word register by 1
40 + rd INC r32 Increment doubleword register by 1


Adds 1 to the destination operand, while preserving the state of the CF flag. The destination operand can be a register or a memory location. This instruction allows a loop counter to be updated without disturbing the CF flag. (Use a ADD instruction with an immediate operand of 1 to perform an increment operation that does updates the CF flag.)

Operands Bytes Clocks
r8 2 1 UV
r16 1 1 UV
r32 1 1 UV
mem 2 + d(0, 2) 3 UV


ID unaffected DF unaffected
VIP unaffected IF unaffected
VIF unaffected TF unaffected
AC unaffected SF sets according to the result
VM unaffected ZF sets according to the result
RF unaffected AF sets according to the result
NT unaffected PF sets according to the result
IOPL unaffected CF unaffected
OF sets according to the result