1 files changed, 86 insertions, 0 deletions
diff --git a/lib/adds.h b/lib/adds.h
new file mode 100644
index 0000000..6544ce5
--- /dev/null
+++ b/lib/adds.h
@@ -0,0 +1,86 @@
+// SPDX-FileCopyrightText: 2023, Alejandro Colomar <alx@kernel.org>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#ifndef SHADOW_INCLUDE_LIB_ADDS_H_
+#define SHADOW_INCLUDE_LIB_ADDS_H_
+
+
+#include <config.h>
+
+#include <errno.h>
+#include <limits.h>
+#include <stddef.h>
+#include <stdlib.h>
+
+#include "sizeof.h"
+
+
+#define addsl(a, b, ...)                                                      \
+({                                                                            \
+	long  addend_[] = {a, b, __VA_ARGS__};                                \
+                                                                              \
+	addslN(NITEMS(addend_), addend_);                                     \
+})
+
+
+inline long addsl2(long a, long b);
+inline long addslN(size_t n, long addend[n]);
+
+inline int cmpl(const void *p1, const void *p2);
+
+
+inline long
+addsl2(long a, long b)
+{
+	if (a > 0 && b > LONG_MAX - a) {
+		errno = EOVERFLOW;
+		return LONG_MAX;
+	}
+	if (a < 0 && b < LONG_MIN - a) {
+		errno = EOVERFLOW;
+		return LONG_MIN;
+	}
+	return a + b;
+}
+
+
+inline long
+addslN(size_t n, long addend[n])
+{
+	int   e;
+
+	if (n == 0) {
+		errno = EDOM;
+		return 0;
+	}
+
+	e = errno;
+	while (n > 1) {
+		qsort(addend, n, sizeof(addend[0]), cmpl);
+
+		errno = 0;
+		addend[0] = addsl2(addend[0], addend[--n]);
+		if (errno == EOVERFLOW)
+			return addend[0];
+	}
+	errno = e;
+	return addend[0];
+}
+
+
+inline int
+cmpl(const void *p1, const void *p2)
+{
+	const long  *l1 = p1;
+	const long  *l2 = p2;
+
+	if (*l1 < *l2)
+		return -1;
+	if (*l1 > *l2)
+		return +1;
+	return 0;
+}
+
+
+#endif  // include guard