2 files changed, 20 insertions, 1 deletions

diff --git a/src/math.c b/src/math.c
index 366bd5e..4e9fee0 100644
--- a/src/math.c
+++ b/src/math.c
@@ -1,6 +1,7 @@
 #include "config.h"
 
 #include <assert.h>
+#include <errno.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdint.h>
@@ -9,8 +10,23 @@
 
 
 int
+add_size(const size_t x, const size_t y, size_t *const out) {
+	int rc = EOVERFLOW;
+
+	const bool overflows = (SIZE_MAX - x) < y;
+	if (overflows) {
+		goto out;
+	}
+
+	*out = x + y;
+	rc = 0;
+out:
+	return rc;
+}
+
+int
 mul_size(const size_t x, const size_t y, size_t *const out) {
-	int rc = -1;
+	int rc = EOVERFLOW;
 
 	assert(x != 0U);
 	assert(y != 0U);
diff --git a/src/math.h b/src/math.h
index 13f1795..4dab4a7 100644
--- a/src/math.h
+++ b/src/math.h
@@ -1,2 +1,5 @@
 int
+add_size(const size_t x, const size_t y, size_t *const out);
+
+int
 mul_size(const size_t x, const size_t y, size_t *const out);