EFLAGS REGISTERS FOR X86 ARCHITECTURE IN MICROPROCESSOR

The EFLAGS is a 32-bit register used as a collection of bits representing Boolean values to store the results of operations and the state of the processor. The names of these bits are : 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 0 0 0 0 0 0 0 0 0 0 ID VIP VIF AC VM RF 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 NT IOPL OF DF IF TF SF ZF 0 AF 0 PF 1 CF The bits named 0 and 1 are reserved bits and shouldn't be modified. The different use of these flags are : 0. CF : Carry Flag. Set if the last arithmetic operation carried (addition) or borrowed (subtraction) a bit beyond the size of the register. This is then checked when the operation is followed with an add-with-carry or subtract-with-borrow to deal with values too large for just one register to contain. 2. PF : Parity Flag. Set if the number of set bits in the least significant byte is a multiple of 2. 4. AF : Adjust Flag. Carry of Binary Code Decimal (BCD) numbers arithmetic operations. 6. ZF : Zero Flag. Set if the result of an operation is Zero (0). 7. SF : Sign Flag. Set if the result of an operation is negative. 8. TF : Trap Flag. Set if step by step debugging. 9. IF : Interruption Flag. Set if interrupts are enabled. 10. DF : Direction Flag. Stream direction. If set, string operations will decrement their pointer rather than incrementing it, reading memory backwards. 11. OF : Overflow Flag. Set if signed arithmetic operations result in a value too large for the register to contain. 12-13. IOPL : I/O Privilege Level field (2 bits). I/O Privilege Level of the current process. 14. NT : Nested Task flag. Controls chaining of interrupts. Set if the current process is linked to the next process. 16. RF : Resume Flag. Response to debug exceptions. 17. VM : Virtual-8086 Mode. Set if in 8086 compatibility mode. 18. AC : Alignment Check. Set if alignment checking of memory references is done. 19. VIF : Virtual Interrupt Flag. Virtual image of IF. 20. VIP : Virtual Interrupt Pending flag. Set if an interrupt is pending. 21. ID : Identification Flag. Support for CPUID instruction if can be set.