From: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Date: Thu, 12 May 2022 14:29:48 +0000 (+0200)
Subject: Add saturate_add() that generalizes size_add()
X-Git-Tag: v251-rc3~8^2~5
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=8b0c43475a764080299f1d69efc2cef0db7b6c66;p=thirdparty%2Fsystemd.git

Add saturate_add() that generalizes size_add()
---

diff --git a/src/basic/macro.h b/src/basic/macro.h
index 3bf982803d5..e6f89608f49 100644
--- a/src/basic/macro.h
+++ b/src/basic/macro.h
@@ -457,8 +457,15 @@ static inline int __coverity_check_and_return__(int condition) {
                 _copy;                                                  \
         })
 
+#define saturate_add(x, y, limit)                                       \
+        ({                                                              \
+                typeof(limit) _x = (x);                                 \
+                typeof(limit) _y = (y);                                 \
+                _x > (limit) || _y >= (limit) - _x ? (limit) : _x + _y; \
+        })
+
 static inline size_t size_add(size_t x, size_t y) {
-        return y >= SIZE_MAX - x ? SIZE_MAX : x + y;
+        return saturate_add(x, y, SIZE_MAX);
 }
 
 typedef struct {
diff --git a/src/test/test-macro.c b/src/test/test-macro.c
index ba319953cd8..c39f64b385e 100644
--- a/src/test/test-macro.c
+++ b/src/test/test-macro.c
@@ -6,6 +6,15 @@
 #include "macro.h"
 #include "tests.h"
 
+TEST(saturate_add) {
+        assert_se(saturate_add(1, 2, UINT8_MAX) == 3);
+        assert_se(saturate_add(1, UINT8_MAX-2, UINT8_MAX) == UINT8_MAX-1);
+        assert_se(saturate_add(1, UINT8_MAX-1, UINT8_MAX) == UINT8_MAX);
+        assert_se(saturate_add(1, UINT8_MAX, UINT8_MAX) == UINT8_MAX);
+        assert_se(saturate_add(2, UINT8_MAX, UINT8_MAX) == UINT8_MAX);
+        assert_se(saturate_add(60, 60, 50) == 50);
+}
+
 TEST(align_power2) {
         unsigned long i, p2;