1 files changed, 14 insertions, 6 deletions

diff --git a/mortgage_loan.c b/mortgage_loan.c
index 386828a..2959214 100644
--- a/mortgage_loan.c
+++ b/mortgage_loan.c
@@ -2,14 +2,12 @@
 
 contract *mort_init(int n, int d, float r, float P) {
 	if ((n < 0)) return NULL;
-	if ((d > n)||(d < 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;
-	c->A = - (P * r * powf(1.0f + r, (float)n));
-	c->A = c->A / (1.0f - powf(1.0f + r, (float)n));
 
 	return c;
 }
@@ -17,11 +15,21 @@ contract *mort_init(int n, int d, float r, float P) {
 float mort_update(contract *c) {
 	if (c->k > c->n)
 		return 0.0f;
+
+	if (c->k == c->d) {
+		c->A = - (c->P * c->r * powf(1.0f + c->r, (float)(c->n - c->k)));
+		c->A = c->A / (1.0f - powf(1.0f + c->r, (float)(c->n - c->k)));
+	}
 	c->k++;
 	c->I = c->r * c->P;
-	c->D = c->A - c->I;
-	c->P = c->P - c->D;
-	/* c->A is fixed ! */
+
+	if (c->k <= c->d)
+		c->P += c->I;
+	else {
+		c->D = c->A - c->I;
+		c->P = c->P - c->D;
+		/* c->A is fixed ! */
+	}
 
 	return c->A;
 }