3C ib         CMP AL, imm8                 Compare imm8 with AL

3D iw         CMP AX, imm16                 Compare imm16 with AX

3D id         CMP EAX, imm32                 Compare imm32 with EAX

80 /7 ib         CMP r/m8, imm8                 Compare imm8 with r/m8

81 /7 iw         CMP r/m16, imm16                 Compare imm16 with r/m16

81 /7 id         CMP r/m32,imm32                 Compare imm32 with r/m32

83 /7 ib         CMP r/m16,imm8                 Compare imm8 with r/m16

83 /7 ib         CMP r/m32,imm8                 Compare imm8 with r/m32

38 / r         CMP r/m8,r8                 Compare r8 with r/m8

39 / r         CMP r/m16,r16                 Compare r16 with r/m16

39 / r         CMP r/m32,r32                 Compare r32 with r/m32

3A / r         CMP r8,r/m8                 Compare r/m8 with r8

3B / r         CMP r16,r/m16                 Compare r/m16 with r16

3B / r         CMP r32,r/m32                 Compare r/m32 with r32


Description

Compares the first source operand with the second source operand and sets the status flags in the EFLAGS register according to the results. The comparison is performed by subtracting the second operand from the first operand and then setting the status flags in the same manner as the SUB instruction. When an immediate value is used as an operand, it is sign-extended to the length of the first operand.


The CMP instruction is typically used in conjunction with a conditional jump (Jcc), condition move (CMOVcc), or SETcc instruction. The condition codes used by the Jcc, CMOVcc, and SETcc instructions are based on the results of a CMP instruction. Appendix B, EFLAGS Condi-tion Codes, in the Intel Architecture Software Developer's Manual, Volume 1, shows the rela-tionship of the status flags and the condition codes.


Operands        Bytes                Clocks

reg, reg             2                       1   UV

mem, reg          2+d(0,2)         2   UV

reg, mem          2+d(0,2)         2   UV

reg, imm          2+i(1,2)           1   UV

mem, imm          2+d(0,2)+i(1,2)        2   UV*

acc, imm          1+i(1,2)           1   UV


* = not pairable if there is a displacement and immediate


Flags

The CF, OF, SF, ZF, AF, and PF flags are set according to the result.

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