I guess subtraction works!?
This commit is contained in:
Simon Forman
parent
70b8bbdc0e
commit
4cea474166
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@ -1,3 +1,4 @@
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from copy import copy
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from itertools import zip_longest
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from pprint import pprint as P
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import unittest
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@ -22,10 +23,10 @@ class BigInt:
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def digitize(n):
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if n < 0:
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raise ValueError(f'Non-negative only: {n}')
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if not n:
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yield OberonInt(0)
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return # Not strictly needed as the following while
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# will not do anything for n == 0.
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#if not n:
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# yield OberonInt(0)
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# return # Not strictly needed as the following while
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# # will not do anything for n == 0.
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while n:
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n, digit = divmod(n, 2**31)
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yield OberonInt(digit)
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@ -43,12 +44,33 @@ class BigInt:
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n = -n
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return n
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def negate(self):
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result = BigInt()
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result.sign = not self.sign
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result.digits = [
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OberonInt(digit.value ^ 2**31 - 1)
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for digit in self.digits
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]
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return result
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def __add__(self, other):
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if not isinstance(other, BigInt):
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other = BigInt(other)
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if self.sign == other.sign:
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return self.add_like_signs(other)
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return self.add_unlike_signs(other)
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def __sub__(self, other):
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if not isinstance(other, BigInt):
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other = BigInt(other)
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#print(23)
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#print(self.to_int(), '-', other.to_int())
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z = copy(other)
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z.sign = not z.sign
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#print(self.to_int(), '+', z.to_int(), 'sub')
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return self + z
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def add_like_signs(self, other):
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'''
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Add a BigInt of the same sign as self.
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@ -71,6 +93,108 @@ class BigInt:
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result.digits = out
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return result
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def add_unlike_signs(self, other):
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'''
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Add a BigInt of unlike sign as self.
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'''
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assert self.sign != other.sign
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# So we have -a and +b
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# or +a and -b
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if self.sign:
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a, b = self, other
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else:
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b, a = self, other
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#print(a.to_int(), '+', b.to_int(), 'add_unlike_signs')
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# So now we have:
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# a + (-b) == a - b
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# I don't know how to subtract a larger (abs) number
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# from a smaller (abs) one
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# However:
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#
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# a - b == -(b - a)
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#
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# I.e. 9 - 17 == -(17 - 9)
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#if abs(a) < abs(b):
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if not a.abs_gt_abs(b):
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#print(f'abs({a.to_int()}) < abs({b.to_int()})')
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x = b._subtract_smaller(a)
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x.sign = not x.sign
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return x
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#print(f'abs({a.to_int()}) > abs({b.to_int()})')
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return a._subtract_smaller(b)
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def _subtract_smaller(self, other):
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assert self.abs_gt_abs(other)
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out = []
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carry = 0
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Z = zip_longest(
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self.digits,
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other.digits,
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fillvalue=zero,
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)
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#P(list(Z))
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for a, b in Z:
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carry, digit = a.sub_with_carry(b, carry)
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out.append(digit)
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if carry:
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out.append(one)
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result = BigInt()
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result.sign = self.sign
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result.digits = out
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return result
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def abs_gt_abs(self, other):
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a_len, b_len = len(self.digits), len(other.digits)
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if a_len > b_len: return True
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if a_len < b_len: return False
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# a_len == b_len
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if not a_len: # a == b == 0
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return False
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return self.digits[-1] > other.digits[-1]
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## result = BigInt()
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## result.sign = self.sign
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## result.digits = (
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## self.subtract_digits(other)
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## if self.sign else
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## other.subtract_digits(self)
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## )
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## return result
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## def subtract_digits(self, other):
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## return []
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##def _sort_key(list_of_obint):
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## n = len(list_of_obint)
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## last = list_of_obint[-1] if n else None
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## return n, zero
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##def subtract_list_of_obints(A, B):
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## L = [A, B]
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## K = sorted(L, key=_sort_key)
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## A, B = K
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## swapped = L != K
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## carry = 0
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## out = []
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## for a, b in zip_longest(A, B, fillvalue=zero):
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## carry, digit = a.sub_with_carry(b, carry)
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## out.append(digit)
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## if carry:
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## out.append(one)
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## result = BigInt()
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## result.sign = self.sign
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## result.digits = out
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## return result
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class OberonInt:
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'''
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@ -94,6 +218,24 @@ class OberonInt:
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assert not z, repr(z)
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return c, digit
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def sub_with_carry(self, other, carry):
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'''
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In terms of single base-10 skool arithmetic:
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a, b in {0..9}
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carry in {0..1}
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0 - 9 - 1
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9 + 9 + 1 = 18 + 1 = 19
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aka = 1,(8+1) = 1, 9
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'''
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c, digit = self - other
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if carry:
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z, digit = digit - one
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assert not z, repr(z)
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return c, digit
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def __init__(self, initial=0):
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assert is_i32(initial)
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self.value = initial
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@ -211,6 +353,33 @@ class BigIntTest(unittest.TestCase):
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t = z.to_int()
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self.assertEqual(t, n + m)
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def test_Addition_of_unlike_signs(self):
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n = 12345678901234567898090123445678990
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m = -901234567898090
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x = BigInt(n)
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y = BigInt(m)
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z = x + y
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t = z.to_int()
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self.assertEqual(t, n + m)
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def _test_invert(self):
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n = 7 * (2**16)
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x = BigInt(n)
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y = x.negate()
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print()
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print(y.to_int(), bin(y.to_int()), y.digits)
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print(x.to_int(), bin(x.to_int()), x.digits)
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print()
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print(x + y)
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def test_Subtraction(self):
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n = 12345678901234567898090123445678990
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m = 901234567898090
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x = BigInt(n)
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y = BigInt(m)
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z = x - y
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t = z.to_int()
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self.assertEqual(t, n - m)
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if __name__ == '__main__':
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@ -225,5 +394,3 @@ if __name__ == '__main__':
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## raise ValueError(f'too big: {initial!r}')
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## if initial < -2**31:
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## raise ValueError(f'too small: {initial!r}')
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