Multiply-Subtract multiplies two register values, subtracts the product from a third register value, and writes the result to the destination register.
乘法-减法将两个寄存器值相乘，从第三个寄存器值中减去乘积，并将结果写入目标寄存器。
32-bit variant
Applies when sf == 0.
MSUB <Wd>, <Wn>, <Wm>, <Wa>
64-bit variant
Applies when sf == 1.
MSUB <Xd>, <Xn>, <Xm>, <Xa>
Decode for all variants of this encoding
integer d = UInt(Rd);
integer n = UInt(Rn);
integer m = UInt(Rm);
integer a = UInt(Ra);
integer destsize = if sf == '1' then 64 else 32;
Operation
bits(destsize) operand1 = X[n];
bits(destsize) operand2 = X[m];
bits(destsize) operand3 = X[a];
integer result;
result = UInt(operand3) - (UInt(operand1) * UInt(operand2));
X[d] = result<destsize-1:0>;
412f98: 8b20d380 add x0, x28, w0, sxtw #4
412f9c: 52800022 mov w2, #0x1 // #1
412fa0: 39004002 strb w2, [x0, #16]
412fa4: 34ffe9c3 cbz w3, 412cdc <ferror@plt+0x10dfc>
412fa8: 1ac30cc2 sdiv w2, w6, w3
412fac: 1b039843 msub w3, w2, w3, w6
