8. Jumps Based on Comparison of Two Values

• The CMP instruction is a common way to test for conditional jumps.

• CMP instruction is the same as the SUB instruction, except that CMP does not change the destination operand. Both set flags according to the result of the subtraction.

• CMP compares signed or unsigned values, but program must choose appropriate conditional jump to reflect the correct type.

• Failure to understand the difference between conditional jump instructions may result in program bugs.

  Conditional Jumps Based on Comparisons of Two Values

  Signed Comparisons		Unsigned Comparisons
  Instruction	Jump if True	Instruction	Jump if True
  JE	ZF = 1	JE	ZF = 1
  JNE	ZF = 0	JNE	ZF = 0
  JG/JNLE	ZF = 0 and SF = OF	JA/JNBE	CF = 0 and ZF = 0
  JLE/JNG	ZF = 1 or SF OF	JBE/JNA	CF = 1 or ZF = 1
  JL/JNGE	SF OF	JB/JNAE	CF = 1
  JGE/JNL	SF = OF	JAE/JNB	CF = 0