RISC-V Decisions II

Logical Instruction

and, andi, not

2种对应变体

• and: and x5, x6, x7 # x5 = x6 & x7
• andi: andi x5, x6, 0x7 # x5 = x6 & 0x7 # for masking 😋
• or: or x5, x6, x7 # x5 = x6 | x7
• xor: xor x5, x6, x7 # x5 = x6 ^ x7

Not not, xor with 111111…1111即可

shift instructions

logical shift

arithmetic shift

A bit about machine programming

PC: program counter (special register), 程序计数器 指向下一条指令的地址（next 4 byte / 1 word away）

side note:

• symbolic name
• pseudo code

Function calls

6 steps to call a function:

conventions

in RISC-V, all instructions are 32-bit long, and stored in memory just like any other data. so below we show the address of where the programs are stored in memory.

• 8个ar
• 1个ra
• 12个sr

新的jump:

• jr: jr ra (return from subroutine) 正是 ret 的具体实现
• jalr : jalr rd, rs, imm jump and link register, 跳转到指定地址并保存返回地址到ra
• jal : jal FunctionLabel / jal rd, Label

事实上，没有jr，j

1

j: jal x0, Label # 跳转到Label并保存返回地址到x0