Calculate the number of distinct floats between two numbers.

distinct_floats.py

"""
Calculate the number of distinct floats between two numbers via bit packing and
unpacking.
--------------------------------------------------------------------------------
>>> distinct_floats(1, 0)
4607182418800017408
>>> distinct_floats(-1, 0)
4616189618054758400
>>> distinct_floats(0, float('inf'))
9218868437227405312

# When the inputs are of opposite sign, the results stop making sense because the 
# unpacked values hit the limits of what can be represented as a long integer.
>>> distinct_floats(-1, 1)
9223372036854775808
>>> distinct_floats(float('inf'), float('-inf'))
9223372036854775808
>>> np.iinfo(np.int)
iinfo(min=-9223372036854775808, max=9223372036854775807, dtype=int64)
"""
import struct
import numpy as np


def distinct_floats(a, b):
    """Return the number of distinct floats between `a` and `b`"""
    # Handle the case where inputs have opposite signs
    if np.sign(a)*np.sign(b) == -1:
        return float_range(a, 0) + float_range(b, 0)
    else:
        tmp = struct.pack('dd', a, b)
        res = struct.unpack('ll', tmp)
        return abs(res[1] - res[0])