uni-m.cds-adv-prog/ex1.5/base32.cpp

/*
 * Print a base10 number in base32
 *
 * Using a multiple of bits, arithmetic is done very fast
 * since cpus talk bits, we can use bit operations which are faster
 *+ than regular (base10) operations
 *
 * also, in base 2^k you can see the splitting on bits
 * with k the amount of bits used to represent the character
 * =>
 * b2: "1100001010100101"
 * b10: "49829"
 * ==
 * b2 per 4 bits: "1100 0010 1010 0101"
 * b10: "12 2 10 5"
 * b16: "C  2 A  5"
 * ==
 * b2 per 5 bits: "(0000)1 10000 10101 00101"
 * b10: "1 16 21 5"
 * b32: "1 G  L  5"
 */

#include <iostream>
#include <cmath>

#define VERBOSE true

char b32_lookup_table[] = "0123456789ABCDEFGHIJKLMNOPQRSTUV";
int base = 32;

int main() {
	//a
	unsigned int number = 16384;
	// get the input unsigned integer
	std::cout << "Enter a Positive Integer: ";
	std::cin >> number;
	
	if ( VERBOSE ) {
		std::cout << "Number " << number << std::endl;
		std::cout << "Base " << base << std::endl;
	}

	//b
	int bits_in_char = log(base)/log(2);// 5 = log2(32)
	int bits_in_int = 8 * sizeof(int);// 32 bits
	
	int chars_per_int = std::ceil(bits_in_int / bits_in_char);// 7 chars needed

	if ( VERBOSE ) {
		std::cout << "Chars per int = " << chars_per_int << " ( " << bits_in_int << " / " << bits_in_char << " ) " << std::endl;
	}

	//c
	unsigned short digits[chars_per_int];

	//d & e
	short digit_num = 0;
	short lsb_bitmask = ( 1 << bits_in_char ) - 1;// 00011111 = 0x1F

	if ( VERBOSE ) {
		std::cout << "Bitmask = 0x" << std::uppercase << std::hex << lsb_bitmask << std::dec << std::endl;
		std::cout << std::endl;
	}

	// Loop until the remainder is 0
	// I'm truncating all 0s in front of MSB
	while ( number > 0 )
	{
		if ( VERBOSE ) {
			std::cout << "Entering loop with number = " << number << std::endl;
			std::cout << " - b16: 0x" << std::hex << number << std::dec << std::endl;
		}
		
		// Mask with the last 5 bits
		digits[digit_num] = number & lsb_bitmask;
		
		// Shift off the bits we have put in to the array
		number >>= bits_in_char;

		++digit_num;
	}
	--digit_num;

	if ( VERBOSE ) {
		std::cout << "We have " << digit_num + 1 << " digits" << std::endl;
		std::cout << std::endl;
	}


	//f
	// Loop the other way so the first digit we get out is MSB
	while ( digit_num >= 0 ) 
	{
		std::cout << b32_lookup_table[digits[digit_num]];

		digit_num--;
	}

	std::cout << std::endl;

	return 0;
}