CODEWITHSUNDEEP
pythonfloating-point
Ecir Hana
Ecir Hana

Reputation: 11508

Test if two floating point numbers within 1 ULP

How to find out whether the difference between two floating-point numbers is at most 1 ULP?

Something like the code below, which (ignores the signs and exponent, and) extracts the binary of mantissa, but slightly less awful:

a = int(<float>.hex().lstrip('-').lstrip('0x')[1:].lstrip('.')[:-3].rstrip('+').rstrip('p'), 16)
b = int(<float>.hex().lstrip('-').lstrip('0x')[1:].lstrip('.')[:-3].rstrip('+').rstrip('p'), 16)
print abs(a - b) <= 1

Upvotes: 2

Views: 1516

Answers (1)

user2357112
user2357112

Reputation: 281594

With NumPy, you can get the next floating-point number after a given number:

# Test whether taking the smallest possible step from b in the direction of a gets you a.
# Special case: If b == a, then np.nextafter(b, a) == a
a == np.nextafter(b, a)

(This might not quite be what you want if, say, the two numbers have different ULPs, or if one is an infinity.)

Upvotes: 1

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