1 files changed, 96 insertions, 0 deletions
diff --git a/src/integer.h b/src/integer.h
new file mode 100644
index 000000000..8e86a48a5
--- /dev/null
+++ b/src/integer.h
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) the libgit2 contributors. All rights reserved.
+ *
+ * This file is part of libgit2, distributed under the GNU GPL v2 with
+ * a Linking Exception. For full terms see the included COPYING file.
+ */
+#ifndef INCLUDE_integer_h__
+#define INCLUDE_integer_h__
+
+/** @return true if p fits into the range of a size_t */
+GIT_INLINE(int) git__is_sizet(git_off_t p)
+{
+	size_t r = (size_t)p;
+	return p == (git_off_t)r;
+}
+
+/** @return true if p fits into the range of an ssize_t */
+GIT_INLINE(int) git__is_ssizet(size_t p)
+{
+	ssize_t r = (ssize_t)p;
+	return p == (size_t)r;
+}
+
+/** @return true if p fits into the range of a uint32_t */
+GIT_INLINE(int) git__is_uint32(size_t p)
+{
+	uint32_t r = (uint32_t)p;
+	return p == (size_t)r;
+}
+
+/** @return true if p fits into the range of an unsigned long */
+GIT_INLINE(int) git__is_ulong(git_off_t p)
+{
+	unsigned long r = (unsigned long)p;
+	return p == (git_off_t)r;
+}
+
+/** @return true if p fits into the range of an int */
+GIT_INLINE(int) git__is_int(long long p)
+{
+	int r = (int)p;
+	return p == (long long)r;
+}
+
+/**
+ * Sets `one + two` into `out`, unless the arithmetic would overflow.
+ * @return true if the result fits in a `uint64_t`, false on overflow.
+ */
+GIT_INLINE(bool) git__add_uint64_overflow(uint64_t *out, uint64_t one, uint64_t two)
+{
+	if (UINT64_MAX - one < two)
+		return true;
+	*out = one + two;
+	return false;
+}
+
+/* Use clang/gcc compiler intrinsics whenever possible */
+#if (SIZE_MAX == UINT_MAX) && __has_builtin(__builtin_uadd_overflow)
+# define git__add_sizet_overflow(out, one, two) \
+	__builtin_uadd_overflow(one, two, out)
+# define git__multiply_sizet_overflow(out, one, two)
+	__builtin_umul_overflow(one, two, out)
+#elif (SIZE_MAX == ULONG_MAX) && __has_builtin(__builtin_uaddl_overflow)
+# define git__add_sizet_overflow(out, one, two) \
+	__builtin_uaddl_overflow(one, two, out)
+# define git__multiply_sizet_overflow(out, one, two) \
+	__builtin_umull_overflow(one, two, out)
+#else
+
+/**
+ * Sets `one + two` into `out`, unless the arithmetic would overflow.
+ * @return true if the result fits in a `size_t`, false on overflow.
+ */
+GIT_INLINE(bool) git__add_sizet_overflow(size_t *out, size_t one, size_t two)
+{
+	if (SIZE_MAX - one < two)
+		return true;
+	*out = one + two;
+	return false;
+}
+
+/**
+ * Sets `one * two` into `out`, unless the arithmetic would overflow.
+ * @return true if the result fits in a `size_t`, false on overflow.
+ */
+GIT_INLINE(bool) git__multiply_sizet_overflow(size_t *out, size_t one, size_t two)
+{
+	if (one && SIZE_MAX / one < two)
+		return true;
+	*out = one * two;
+	return false;
+}
+
+#endif
+
+#endif /* INCLUDE_integer_h__ */