MMIX Instruction Set
Content
NEG and NEGU
Name:| NEG $X,Y,$Z | NEG $X,Y,Z |
| NEGU $X,Y,$Z | NEGU $X,Y,Z |
Specification:
| NEG: s($X) | ← Y - s($Z) |
| NEGU: u($X) | ← (Y - u($Z)) mod 264 |
Timing:
1υ
Description:
Y is a nonnegative constant, usually zero. If Y has the value zero, it can be omitted. The instruction is used to negate $Z.
| NEG: | The value Y - $Z or Y - Z is placed into register $X using signed, two's complement arithmetic. An integer overflow exception occurs if the result is greater than 263 - 1. (Notice that in this case MMIX works with the "immediate" constant Y, not register $Y. NEG commands are analogous to the immediate variants of other commands, because they save us from having to put one-byte constants into a register. When Y = 0, overflow occurs if and only if $Z = -263 . The instruction NEG $X,1,2 has exactly the same effect as NEG $X,0,1) |
| NEGU: | The value (Y - $Z) mod 264 or (Y - Z) mod 264 is placed into register $X. NEGU instructions are the same as NEG instructions, except that no test for overflow is made. |
