ARM base instruction -- umull
无符号乘法运算
Unsigned Multiply Long multiplies two 32-bit register values, and writes the result to the 64-bit destination register.
将两个32位寄存器值相乘，并将结果写入64位目标寄存器。
64-bit variant
UMULL <Xd>, <Wn>, <Wm>
is equivalent to
UMADDL <Xd>, <Wn>, <Wm>, XZR
416b48: 5290a3e2 mov w2, #0x851f // #34079
416b4c: aa1403e1 mov x1, x20
416b50: 72aa3d62 movk w2, #0x51eb, lsl #16
416b54: 9ba27ea2 umull x2, w21, w2