9.md

算术指令

add

全称：add

语法：add rd, rs1, rs2

操作：x[rd] = x[rs1] + x[rs2]

R	31 - 25	24 - 20	19 - 15	14 - 12	11 - 7	6 - 0
	0000000	rs2	rs1	000	rd	0110011

addi

全称：add immediate

语法：addi rd, rs1, imm

操作：x[rd] = x[rs1] + sext(immediate)

I	31 - 20	19 - 15	14 - 12	11 - 7	6 - 0
	imm[11:0]	rs1	000	rd	0010011

sub

全称：subtract

语法：sub rd, rs1, rs2

操作：x[rd] = x[rs1] - sext(immediate)

R	31 - 25	24 - 20	19 - 15	14 - 12	11 - 7	6 - 0
	0100000	rs2	rs1	000	rd	0110011

lui

全称：load upper immediate

语法：lui rd, imm

auipc

全称：add upper immediate to pc

语法：lui rd, imm

例程1：加减运算

计算 12+34-56

  .globl main
main:
  addi a0, zero, 12
  addi a0, a0, 34
  addi a0, a0, -56