pythonnumpyhalf-precision-float

Convert 16 bit hex value to FP16 in Python?

I'm trying to write a basic FP16 based calculator in python to help me debug some hardware. Can't seem to find how to convert 16b hex values unto floating point values I can use in my code to do the math. I see lots of online references to numpy but I think the float16 constructor expects a string like float16("1.2345"). I guess what I'm looking for is something like float16("0xabcd").

Thanks!

Solution

  • The numpy.float16 is indeed a signed floating point format with a 5-bit exponent and 10-bit mantissa.

    To get the result of your example:

    import numpy as np

np.frombuffer(b'\xab\xcd', dtype=np.float16, count=1)

    Result:

    array([-22.67], dtype=float16)

    Or, to show how you can encode and decode the other example 1.2345:

    import numpy as np

a = np.array([1.2345], numpy.float16)
b = a.tobytes()
print(b)
c = np.frombuffer(b, dtype=np.float16, count=1)
print(c)

    Result:

    b'\xf0<'
[1.234]

    If you literally needed to turn the string you provided into an FP16:

    import numpy as np

s = "0xabcd"
b = int("0xabcd", base=16).to_bytes(2, 'big')
print(b)
c = np.frombuffer(b, dtype=np.float16, count=1)
print(c)

    Output:

    b'\xab\xcd'
[-22.67]