func 在 R-Format 指令集中意味着什么？

I am very new to Assembly language. I was reading about MIPS architecture and I am stuck with the last field of the Register Format (R-Format). Here is its visual representation, Can anyone please help me out with what does the sixth field means and how do we calculate it? Thanks in advance.

正如描述中提到的所有 R 类型指令（例如ADD, AND, SLL和其他）的 6 个最高有效位 (= op) 设置为 0，这意味着区分它们的唯一方法是查看 6 个最低有效位 (= funct)。换句话说，它们决定指令类型。也许一个例子会有所帮助：

ADD $1, $2, $3 

has:

op = 0 (as all R-type instructions)
rs = 2
rt = 3
rd = 1
shamt = 0
funct = 0x20 = 0b00000100000 = 32

因此，编码将是：

0000 0000 0100 0011 0000 1000 0010 0000

例如XOR（另一种R型）指令函数是0b100110 = 0x26 = 38。因此，您可以通过查找要编码的指令来“计算”它。

（取自MIPS指令参考 http://www.mrc.uidaho.edu/mrc/people/jff/digital/MIPSir.html).