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BigIntMod.py
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BigIntMod.py
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"""
Title: Big Int Mod
Given a list of bytes a, each representing one byte of a larger integer
(ie. {0x12, 0x34, 0x56, 0x78} represents the integer 0x12345678), and an
integer b, find a % b.
Execution: python BigIntMod.py
For more details, check out http://www.byte-by-byte.com/bigintmod/
"""
import unittest
def big_int_mod(a: list, b: int):
if a is None:
return 0
m = 0
for i in range(len(a)):
m <<= 8
m += (a[i] & 0xFF)
m %= b
return m
class TestBigIntMod(unittest.TestCase):
def test_null_value(self):
self.assertEqual(big_int_mod(None, 1), 0)
print("Null value.")
def test_empty_array(self):
self.assertEqual(big_int_mod([], 1), 0)
print("Empty array.")
def test_single_element_array(self):
self.assertEqual(big_int_mod([15], 10), 5)
print("Single element array.")
def test_multi_element_array(self):
self.assertEqual(big_int_mod([0x03, 0xED], 10), 5)
print("Multi-element array")
if __name__ == '__main__':
unittest.main()