diff --git a/misc/factorial_fast.c b/misc/factorial_fast.c new file mode 100644 index 00000000..2559aaca --- /dev/null +++ b/misc/factorial_fast.c @@ -0,0 +1,67 @@ +#include +#include +#include + +/** + Returns the \f$n^{th}\f$ and \f$n+1^{th}\f$ Fibonacci number. + The return variables are C & D respectively. + */ +void fib(unsigned long n, unsigned long *C, unsigned long *D) +{ + //Out of Range checking + if (n < 0) + { + printf("\nNo Such term !\n"); + exit(0); + } + + unsigned long a, b, c, d; + + if (n == 0) + { + C[0] = 0; + if (D) + D[0] = 1; + return; + } + + fib(n >> 1, &c, &d); /**< Compute F(n/2) */ + + a = c * ((d << 1) - c); + b = c * c + d * d; + if (n % 2 == 0) /**< If n is even */ + { + C[0] = a; + if (D) + D[0] = b; + return; + } + + /**< If n is odd */ + C[0] = b; + if (D) + D[0] = a + b; + return; +} + +int main(int argc, char *argv[]) +{ + unsigned long number, result; + + setlocale(LC_NUMERIC, ""); // format the printf output + + //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("%lu", &number); + } + + fib(number, &result, NULL); + + printf("The nth term is : %'lu \n", result); + + return 0; +}