straight_line_loan.c


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#include "loans.h"

contract *sl_init(int n, int d, double r, double P) {
	if ((n < 0)) return NULL;
	if ((d >= n)||(d < 0)) return NULL;
	contract *c = (contract *)calloc(1, sizeof(contract));
	c->n = (unsigned int)n;
	c->d = (unsigned int)d;
	c->r = r;
	c->P = P;

	return c;
}

double sl_update(contract *c) {
	if (c->k > c->n)
		return 0.0;

	if (c->k == c->d) c->D = c->P/(double)(c->n - c->k);
	c->k++;
	c->I = c->r * c->P;

	if (c->k <= c->d)
		c->P += c->I;
	else {
		c->P = c->P - c->D;
		c->A = c->D + c->I;
		/* c->D is fixed ! */
	}

	return c->A;
}

void sl_free(contract *c) {
	free(c);
}