How to convert a decimal base (10) to a negabinary base (-2)?
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30-04-2021 - |
質問
I want to write a program to convert from decimal to negabinary.
I cannot figure out how to convert from decimal to negabinary.
I have no idea about how to find the rule and how it works.
Example: 7(base10)-->11011(base-2)
I just know it is 7 = (-2)^0*1 + (-2)^1*1 + (-2)^2*0 + (-2)^3*1 + (-2)^4*1
.
解決
The algorithm is described in http://en.wikipedia.org/wiki/Negative_base#Calculation. Basically, you just pick the remainder as the positive base case and make sure the remainder is nonnegative and minimal.
7 = -3*-2 + 1 (least significant digit)
-3 = 2*-2 + 1
2 = -1*-2 + 0
-1 = 1*-2 + 1
1 = 0*-2 + 1 (most significant digit)
他のヒント
Just my two cents (C#):
public static int[] negaBynary(int value)
{
List<int> result = new List<int> ();
while (value != 0)
{
int remainder = value % -2;
value = value / -2;
if (remainder < 0)
{
remainder += 2;
value += 1;
}
Console.WriteLine (remainder);
result.Add(remainder);
}
return result.ToArray();
}
There is a method (attributed to Librik/Szudzik/Schröppel) that is much more efficient:
uint64_t negabinary(int64_t num) {
const uint64_t mask = 0xAAAAAAAAAAAAAAAA;
return (mask + num) ^ mask;
}
The conversion method and its reverse are described in more detail in this answer.
def neg2dec(arr):
n = 0
for i, num in enumerate(arr[::-1]):
n+= ((-2)**i)*num
return n
def dec2neg(num):
if num == 0:
digits = ['0']
else:
digits = []
while num != 0:
num, remainder = divmod(num, -2)
if remainder < 0:
num, remainder = num + 1, remainder + 2
digits.append(str(remainder))
return ''.join(digits[::-1])
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