110 lines
2.4 KiB
C++
110 lines
2.4 KiB
C++
/*
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* Print a base10 number in base32
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*
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* Using a multiple of bits, arithmetic is done very fast
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* since cpus talk bits, we can use bit operations which are faster
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*+ than regular (base10) operations
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*
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* also, in base 2^k you can see the splitting on bits
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* with k the amount of bits used to represent the character
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* =>
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* b2: "1100001010100101"
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* b10: "49829"
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* ==
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* b2 per 4 bits: "1100 0010 1010 0101"
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* b10: "12 2 10 5"
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* b16: "C 2 A 5"
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* ==
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* b2 per 5 bits: "(0000)1 10000 10101 00101"
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* b10: "1 16 21 5"
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* b32: "1 G L 5"
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*/
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#include <iostream>
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#include <cmath>
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#define VERBOSE false
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char b32_lookup_table[] = "ABCDEFGHIJKLMNOPQRSTUV";
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int base = 8;
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int main() {
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//a
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unsigned int number = 16384;
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// get the input unsigned integer
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std::cout << "Enter a Positive Integer: ";
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std::cin >> number;
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if ( VERBOSE ) {
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std::cout << "Number " << number << std::endl;
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std::cout << "Base " << base << std::endl;
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}
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//b
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int bits_in_char = log(base)/log(2);// 5 = log2(32)
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int bits_in_int = 8 * sizeof(int);// 32 bits
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int chars_per_int = std::ceil(bits_in_int / bits_in_char);// 7 chars needed
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if ( VERBOSE ) {
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std::cout << "Chars per int = " << chars_per_int << " ( " << bits_in_int << " / " << bits_in_char << " ) " << std::endl;
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}
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//c
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unsigned short digits[chars_per_int];
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//d & e
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short digit_num = 0;
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short lsb_bitmask = ( 1 << bits_in_char ) - 1;// 00011111 = 0x1F
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if ( VERBOSE ) {
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std::cout << "Bitmask = 0x" << std::uppercase << std::hex << lsb_bitmask << std::dec << std::endl;
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std::cout << std::endl;
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}
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// Loop until the remainder is 0
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// I'm truncating all 0s in front of MSB
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while ( number > 0 )
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{
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if ( VERBOSE ) {
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std::cout << "Entering loop with number = " << number << std::endl;
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std::cout << " - b16: 0x" << std::hex << number << std::dec << std::endl;
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}
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// Mask with the last 5 bits
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digits[digit_num] = number & lsb_bitmask;
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// Shift off the bits we have put in to the array
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number = ( number >> bits_in_char );
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++digit_num;
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}
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--digit_num;
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if ( VERBOSE ) {
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std::cout << "We have " << digit_num + 1 << " digits" << std::endl;
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std::cout << std::endl;
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}
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//f
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// Loop the other way so the first digit we get out is MSB
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while ( digit_num >= 0 )
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{
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if ( digits[digit_num] < 10 )
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{
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std::cout << digits[digit_num];
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}
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else
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{
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std::cout << b32_lookup_table[digits[digit_num] - 10];
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}
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digit_num--;
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}
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std::cout << std::endl;
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return 0;
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}
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