factorial_large_number.c File Reference

Compute factorial of arbitrarily large numbers by storing individual digits in a byte. More...

#include <stdio.h>
#include <stdlib.h>
#include <time.h>

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Data Structures
struct	_large_num
	dynamically large number More...

Typedefs
typedef struct _large_num	large_num
	dynamically large number

Functions
large_num *	new_number (void)
	create a new large number More...
void	delete_number (large_num *num)
	delete all memory allocated for large number More...
void	add_digit (large_num *num, unsigned int value)
	add a digit to the large number More...
void	multiply (large_num *num, unsigned long n)
	multiply large number with another integer and store the result in the same large number More...
int	main (int argc, char *argv[])
	main function More...

Detailed Description

Compute factorial of arbitrarily large numbers by storing individual digits in a byte.

Author

Krishna Vedala

Function Documentation

add_digit()

void add_digit	(	large_num *	num,
		unsigned int	value
	)

add a digit to the large number

Parameters

[in,out]	num
[in]	value	value of the digit to insert

{
    if (value > 9)
    {
        fprintf(stderr, "digit > 9!!\n");
        delete_number(num);
        exit(EXIT_FAILURE);
    }
 
    num->num_digits++;
    num->digits = (char *)realloc(num->digits, num->num_digits * sizeof(char));
    num->digits[num->num_digits - 1] = value;
}

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delete_number()

void delete_number

(

large_num *

num

)

delete all memory allocated for large number

Parameters

[in]

num

pointer to large_num to delete

{
    free(num->digits);
    free(num);
}

main()

int main	(	int	argc,
		char *	argv[]
	)

main function

{
    int number, i;
 
    // Asks for the number/position of term in Fibonnacci sequence
    if (argc == 2)
        number = atoi(argv[1]);
    else
    {
        printf("Enter the value of n(n starts from 0 ): ");
        scanf("%d", &number);
    }
 
    large_num *result = new_number();
 
    clock_t start_time = clock();
    for (i = 2; i <= number; i++) /* Multiply every number from 2 thru N */
        multiply(result, i);
    double time_taken = (clock() - start_time) * (double)1e3 / CLOCKS_PER_SEC;
    // time_taken = (clock() - start_time) / (double) CLOCKS_PER_SEC;
 
    printf("%d! = ", number);
    for (i = result->num_digits; i > 0; i--)
        putchar(result->digits[i - 1] + '0');
    printf("\nTime taken: %.4g ms\n", time_taken);
 
    delete_number(result);
    return 0;
}

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multiply()

void multiply	(	large_num *	num,
		unsigned long	n
	)

multiply large number with another integer and store the result in the same large number

{
    int i;
    unsigned long carry = 0, temp;
    for (i = 0; i < num->num_digits; i++)
    {
        temp = num->digits[i] * n;
        temp += carry;
        if (temp < 10)
            carry = 0;
        else
        {
            carry = temp / 10;
            temp = temp % 10;
        }
        num->digits[i] = temp;
    }
 
    while (carry != 0)
    {
        add_digit(num, carry % 10);
        carry /= 10;
    }
}

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new_number()

large_num * new_number

(

void

)

create a new large number

Returns

pointer to a large number

{
    large_num *new_num = (large_num *)malloc(sizeof(large_num));
    new_num->num_digits = 1;
    new_num->digits = (char *)malloc(1 * sizeof(char));
    new_num->digits[0] = 1;
    return new_num;
}