A partially implemented rv32i decoder.

rv32i.py

import argparse

alu = {
	'0000':'add',	'1000':'sub',
	'0001':'sll',
	'0010':'slt',
	'0011':'sltu',
	'0100':'xor',
	'0101':'srl',	'1101':'sra',
	'0110':'or',
	'0111':'and'
}
alui = {
	'0000':'addi',	'1000':'addi',
	'0001':'slli',	'1001':'slli',
	'0010':'slti',	'1010':'slti',
	'0011':'sltui',	'1011':'sltui',
	'0100':'xori',	'1100':'xori',
	'0101':'srli',	'1101':'srai',
	'0110':'ori',	'1110':'ori',
	'0111':'andi',	'1111':'andi'
}
load = {
	'000':'lb',
	'001':'lh',
	'010':'lw',
	'100':'lbu',
	'101':'lhu'
}
store = {
	'000':'sb',
	'001':'sh',
	'010':'sw'
}

def decode(instr):
	instr = format(int(instr, 16), '032b')[::-1]
	opcode = instr[:7][::-1]
	rd = instr[7:12][::-1]
	funct3 = instr[12:15][::-1]
	rs1 = instr[15:20][::-1]
	rs2 = instr[20:25][::-1]
	imm = instr[20:32][::-1]
	if opcode == '0100011':
		imm = imm[:7] + rd

	rs1 = int(rs1, 2)
	rs2 = int(rs2, 2)
	rd = int(rd, 2)
	imm = int(imm, 2)
	if (imm & (1 << 11)) != 0:
		imm = imm - (1 << 12)

	# ALU
	if opcode == '0010011': return f'{alui[instr[30]+funct3]}\tr{rd}, r{rs1}, {imm}'
	elif opcode == '0110011': return f'{alu[instr[30]+funct3]}\tr{rd}, r{rs1}, {imm}'

	# Load and Store
	elif opcode == '0000011': return f'{load[funct3]}\t\tr{rd}, {imm}(r{rs1})'
	elif opcode == '0100011': return f'{store[funct3]}\t\tr{rs2}, {imm}(r{rs1})'

	else: return 'Invalid instruction'

parser = argparse.ArgumentParser(description='An rv32i decoder. Use as \'python3 rv32i.py INFILE -o OUTFILE\'')
parser.add_argument('file', action="store", help="File to read from")
parser.add_argument('-o', '--output', help='output filename')
args = parser.parse_args()

with open(args.file) as fp:
	lines = fp.readlines()

outLines = []
for line in lines:
	outLines.append(f'{line[:-2]}\t:\t{decode(line[:8])}\n')

if args.output:
	with open(args.output, 'w') as fp:
		fp.writelines(outLines)
	print(f'Saved output to {args.output}')
	exit(0)

for line in outLines:
	print(line,end='')

Refer to the below image for register nomenclature.