5-bit signed binary to int

Question

My code has to read 5-bit signed binary values. Let's say it reads a 11111, which would be two's complement -1. But int("0b11111", 2) returns 31 instead.

How can I parse the correct value?

I'm writing an emulator, and most of the values are set using 5 bits in the instructions. — William Fernandes, Sep 04 '16 at 19:25
`bin(-1)` is `-0b1`. You'll have to code the two's compliment manually. — Jean-François Fabre, Sep 04 '16 at 19:29

score 1 · Accepted Answer · answered Sep 04 '16 at 19:36

1

Here's a possible solution testing all 5-length binary numbers of your future emulator:

import itertools


def two_complement(value, length):
    if (value & (1 << (length - 1))) != 0:
        value = value - (1 << length)
    return value

opcodes_emulator = ["".join(seq) for seq in itertools.product("01", repeat=5)]

for my_string in opcodes_emulator:
    print my_string, two_complement(int(my_string, 2), len(my_string))

answered Sep 04 '16 at 19:36

BPL

9,632
9
59
117

That's exactly what I was looking for. Thank you! – William Fernandes Sep 04 '16 at 19:42

5-bit signed binary to int

1 Answers1