UVa 11809

Floating-Point Numbers.cpp

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <sstream>
#include <iostream>
#include <vector>

#define MAX_A_DIGIT 10
#define MAX_A_DIGIT_POWER_2 1024
#define TOLERANCE 0.00001

using namespace std;

struct MappingPair {
	double decimalFractionNumber;
	int binaryDigits;
};

vector<MappingPair> decimalFractionMappingTable;

void MakeTable()
{
	int base2WeightTable[MAX_A_DIGIT] = { 512,256,128,64,32,16,8,4,2,1 };
	for (auto i = 1; i < MAX_A_DIGIT_POWER_2; i++)
	{
		auto number = i;
		auto position = 0;
		while (number > 0)
		{
			if (number >= base2WeightTable[position])
			{
				number -= base2WeightTable[position];
			}
			position++;
		}

		auto mappingPair = MappingPair{ log10(1.0 * i / MAX_A_DIGIT_POWER_2), position };
		decimalFractionMappingTable.push_back(mappingPair);
	}
}

bool InputData(double &A, int &B)
{
	auto numberStr = string{};
	if (!(cin >> numberStr))
	{
		return false;
	}

	auto index = numberStr.find('e');
	auto strA = numberStr.substr(0, index);
	auto strB = numberStr.substr(index + 1, numberStr.size() - index);

	stringstream(strA) >> A;
	stringstream(strB) >> B;

	return !(numberStr[0] == '0' && B == 0);
}

int CalculateTotalDigitsInBinary(int decimalNumber)
{
	return (int)(log2(decimalNumber)) + 1;
}

double CalculateDecimalFractionNumber(double A, int B, int twoToThePowerE)
{
	return log10(A) + B - log10(2.0)*twoToThePowerE;
}

double Calculate2ToPowerE(double A, int B)
{
	return (int)(log2(A) + log2(10.0)*abs(B)) + 1;
}

int FindMinimumBinaryDigitsGreaterThan(double fractionNumber)
{
	if (fabs(fractionNumber) <= TOLERANCE)
	{
		return 0.0;
	}

	for (auto index = 0; index < decimalFractionMappingTable.size(); index++)
	{
		auto difference = fabs(decimalFractionMappingTable[index].decimalFractionNumber - fractionNumber);
		if (difference <= TOLERANCE || decimalFractionMappingTable[index].decimalFractionNumber >= fractionNumber)
		{
			return decimalFractionMappingTable[index].binaryDigits - 1;
		}
	}
	return MAX_A_DIGIT;
}

int main()
{
	MakeTable();
	while (true)
	{
		auto A = 0.0;
		auto B = 0;
		if (!InputData(A, B))
		{
			break;
		}

		auto twoToThePowerE = Calculate2ToPowerE(A, B); //2^E
		auto fractionNumber = CalculateDecimalFractionNumber(A, abs(B), twoToThePowerE);
		auto M = FindMinimumBinaryDigitsGreaterThan(fractionNumber);
		auto E = CalculateTotalDigitsInBinary(twoToThePowerE);
		printf("%d %d\n", M, E);
	}
	return 0;
}