Intel Pentium CPU Instruction Set Reference
DEC instruction - Decrement by 1
| Code |
Mnemonic |
Description |
| FE /1 |
DEC r/m8 |
Decrement r/m8 by 1 |
| FF /1 |
DEC r/m16 |
Decrement r/m16 by 1 |
| FF /1 |
DEC r/m32 |
Decrement r/m32 by 1 |
| 48 + rw |
DEC r16 |
Decrement r16 by 1 |
| 48 + rd |
DEC r32 |
Decrement r32 by 1 |
Description
Subtracts 1 from 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. (To perform a decrement operation that updates the CF flag, use a SUB instruction with an immediate operand of 1.)
| Operands |
Bytes |
Clocks |
| r8 |
2 |
1 |
UV |
| r16 |
1 |
1 |
UV |
| r32 |
1 |
1 |
UV |
| mem |
2 + d(0, 2) |
3 |
UV |
Flags
| 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 |
