10、ARM处理器编程：条件执行与有符号数运算详解

ARM处理器编程：条件执行与有符号数运算详解

1. ARM条件执行特性

1.1 条件执行概念

ARM处理器的独特之处在于，所有指令都具备条件执行特性，而非仅分支指令。默认情况下，指令无条件执行，若要使指令有条件执行，需在指令后添加条件语法。ARM指令为条件码预留了最高4位，这4位可表示16种可能的条件，具体如下表所示：
| Bits | Mnemonic Extension | Meaning | Flag |
| ---- | ---- | ---- | ---- |
| 0000 | EQ | Equal | Z = 1 |
| 0001 | NE | Not equal | Z = 0 |
| 0010 | CS/HS | Carry Set/Higher or Same | C = 1 |
| 0011 | CC/LO | Carry Clear/Lower | C = 0 |
| 0100 | MI | Minus/Negative | N = 1 |
| 0101 | PL | Plus | N = 0 |
| 0110 | VS | V Set (Overflow) | V = 1 |
| 0111 | VC | V Clear (No Overflow) | V = 0 |
| 1000 | HI | Higher | C = 1 and Z = 0 |
| 1001 | HS | Lower or Same | C = 1 and Z = 1 |
| 1010 | GE | Greater than or Equal | N = V |
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