ARM base instruction -- mneg
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>;