#! /usr/bin/env python
"""
 Precision.py is a program  which calculate the smallest floating
 point number such that when it is added to the value 1.0 the sum
 due to round-off precision results in a value of 1.0

 Paul Eugenio
 PHZ4151C
 13 Feb 2019
"""
from __future__ import division, print_function
import numpy as np

    
# define lists to hold functions and the function names
#  This make for easy index access to the numpy float types
#
ftype = [ np.float16, np.float32, np.float64, np.float128]   
fname = ["float16", "float32", "float64", "float128"]   

# find the percision for all 4 float types.  Be certain that all variables 
# in an operations are of the same float type.  
for k in range( len(ftype) ):
    eps = ftype[k](1.0)    # same as eps = np.float16(1.0)
    one = ftype[k](1.0)
    two = ftype[k](2.0)
    while one + eps != one:
    	# find eps to within a factor of 2
        eps = eps/two
    
    print(fname[k],": 1.0 + ",eps, "is ", ftype[k](one + eps) )