Multiply-Negate multiplies two register values, negates the product, and writes the result to the destination register.

乘法-求反，将两个寄存器值相乘，对乘积求反，并将结果写入目标寄存器。

32-bit variant
    Applies when sf == 0.
    MNEG <Wd>, <Wn>, <Wm>

64-bit variant
    Applies when sf == 1.
    MNEG <Xd>, <Xn>, <Xm>

Operation
 bits(destsize) operand1 = X[n]; 
 bits(destsize) operand2 = X[m]; 
  
 integer result; 
  
 result = NEG(UInt(operand1) * (UInt(operand2))
 X[d] = result<destsize-1:0>;