From 2180ad3d66d94c8948af1e259fcc8ec10737fb1c Mon Sep 17 00:00:00 2001
From: gonzo <gonzo@toniatuh.com>
Date: Fri, 19 May 2023 11:04:44 +0200
Subject: added mortgage loans

---
 Makefile             |  4 ++--
 loans.h              |  6 ++++++
 mortgage_loan.c      | 31 +++++++++++++++++++++++++++++++
 straight_line_loan.c |  1 +
 4 files changed, 40 insertions(+), 2 deletions(-)
 create mode 100644 mortgage_loan.c

diff --git a/Makefile b/Makefile
index 3446aa7..d3a30d0 100644
--- a/Makefile
+++ b/Makefile
@@ -8,7 +8,7 @@ CC=clang --std=c99
 AR=ar ruvcs
 
 CFLAGS=-Wall -Wextra -Werror -Weverything -Wpadded -pedantic
-LIBS=-lncurses
+LIBS=-lncurses -lm
 BLDFLAGS=-g
 RELFLAGS=-O2
 
@@ -18,7 +18,7 @@ HEAD=
 OBJ=${DEPS:.c=.o}
 
 LIB=las.a
-LDEPS=bullet_loan.c straight_line_loan.c
+LDEPS=bullet_loan.c straight_line_loan.c mortgage_loan.c
 LHEAD=contract.h loans.h
 LOBJ=${LDEPS:.c=.o}
 
diff --git a/loans.h b/loans.h
index 8613028..fd276ae 100644
--- a/loans.h
+++ b/loans.h
@@ -1,5 +1,6 @@
 #pragma once
 #include <stdlib.h>
+#include <math.h>
 #include "contract.h"
 
 /**** BULLET LOAN ****/
@@ -11,3 +12,8 @@ void bullet_free(contract *c);
 contract *sl_init(int n, int d, float r, float P);
 float sl_update(contract *);
 void sl_free(contract *);
+
+/**** MORTGAGE ****/
+contract *mort_init(int n, int d, float r, float P);
+float mort_update(contract *);
+void mort_free(contract *);
diff --git a/mortgage_loan.c b/mortgage_loan.c
new file mode 100644
index 0000000..386828a
--- /dev/null
+++ b/mortgage_loan.c
@@ -0,0 +1,31 @@
+#include "loans.h"
+
+contract *mort_init(int n, int d, float r, float 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;
+	c->A = - (P * r * powf(1.0f + r, (float)n));
+	c->A = c->A / (1.0f - powf(1.0f + r, (float)n));
+
+	return c;
+}
+
+float mort_update(contract *c) {
+	if (c->k > c->n)
+		return 0.0f;
+	c->k++;
+	c->I = c->r * c->P;
+	c->D = c->A - c->I;
+	c->P = c->P - c->D;
+	/* c->A is fixed ! */
+
+	return c->A;
+}
+
+void mort_free(contract *c) {
+	free(c);
+}
diff --git a/straight_line_loan.c b/straight_line_loan.c
index 0d25247..73ba859 100644
--- a/straight_line_loan.c
+++ b/straight_line_loan.c
@@ -20,6 +20,7 @@ float sl_update(contract *c) {
 	c->I = c->r * c->P;
 	c->P = c->P - c->D;
 	c->A = c->D + c->I;
+	/* c->D is fixed ! */
 
 	return c->A;
 }
-- 
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