ARM条件码与CPSR标志位的关系

在ARM体系中，所有ARM指令均可条件执行，设置了一些条件执行码，但这些条件码对应设置CPSR中的Z, C, N, V标志位：

l 0000 = EQ - Z set (equal)

l 0001 = NE - Z clear (not equal)

l 0010 = CS - C set (unsigned higher or same)

l 0011 = CC - C clear (unsigned lower)

l 0100 = MI - N set (negative)

l 0101 = PL - N clear (positive or zero)

l 0110 = VS - V set (overflow)

l 0111 = VC - V clear (no overflow)

l 1000 = HI - C set and Z clear (unsigned higher)

l 1001 = LS - C clear or Z set (unsigned lower or same)

l 1010 = GE - N set and V set, or N clear and V clear (greater or equal)

l 1011 = LT - N set and V clear, or N clear and V set (less than)

l 1100 = GT - Z clear, and either N set and V set, or N clear and V clear (greater than)

l 1101 = LE - Z set, or N set and V clear, or N clear and V set (less than or equal)

l 1110 = AL - always

l 1111 = NV - never

怎样去理解这些设置呢？拿1001 = LS - C clear or Z set (unsigned lower or same)来说：

是为什么LS就对应 C clear and Z set。看下面的例子：

MOV R0, #5

MOV R1, #6

CMP R0, R1

MOVLS R2, R0 ; if R0 < R1 则 将小值存入R2中

在这个例子中，MOVLS 能够正确执行的条件C=0 and z=1 成立，是通过CMP设置了

本文来自CSDN博客，转载请标明出处：http://blog.csdn.net/shansan/archive/2008/10/24/3137216.aspx

if(a>b) a++;
else b++;
对应的ARM指令如下：R0 等于a, R1等于b
CMP R0, R1 ;R0与R1比较
ADDHI R0, R0, #01 ；大于执行R0+=1;
ADDLS R1, R1, #01

If(a != 10 && b != 20) a=a+b;
对应的ARM指令如下：
CMP R0, #10 ;R0与10比较
CMPNE R1, #20 ；不相等执行R1与20比较
ADDNE R0, R0, R1 ；不相等执行R0=R0+R1