1 files changed, 218 insertions, 0 deletions
diff --git a/src/util/integer.h b/src/util/integer.h
new file mode 100644
index 0000000..6327717
--- /dev/null
+++ b/src/util/integer.h
@@ -0,0 +1,218 @@
+/*
+ * 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(int64_t p)
+{
+	size_t r = (size_t)p;
+	return p == (int64_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 uint16_t */
+GIT_INLINE(int) git__is_uint16(size_t p)
+{
+	uint16_t r = (uint16_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(int64_t p)
+{
+	unsigned long r = (unsigned long)p;
+	return p == (int64_t)r;
+}
+
+/** @return true if p fits into the range of an int */
+GIT_INLINE(int) git__is_int(int64_t p)
+{
+	int r = (int)p;
+	return p == (int64_t)r;
+}
+
+/* Use clang/gcc compiler intrinsics whenever possible */
+#if (__has_builtin(__builtin_add_overflow) || \
+     (defined(__GNUC__) && (__GNUC__ >= 5)))
+
+# if (SIZE_MAX == UINT_MAX)
+#  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)
+#  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)
+# elif (SIZE_MAX == ULLONG_MAX)
+#  define git__add_sizet_overflow(out, one, two) \
+     __builtin_uaddll_overflow(one, two, out)
+#  define git__multiply_sizet_overflow(out, one, two) \
+     __builtin_umulll_overflow(one, two, out)
+# else
+#  error compiler has add with overflow intrinsics but SIZE_MAX is unknown
+# endif
+
+# define git__add_int_overflow(out, one, two) \
+    __builtin_sadd_overflow(one, two, out)
+# define git__sub_int_overflow(out, one, two) \
+    __builtin_ssub_overflow(one, two, out)
+
+# define git__add_int64_overflow(out, one, two) \
+    __builtin_add_overflow(one, two, out)
+
+/* clang on 32-bit systems produces an undefined reference to `__mulodi4`. */
+# if !defined(__clang__) || !defined(GIT_ARCH_32)
+#  define git__multiply_int64_overflow(out, one, two) \
+     __builtin_mul_overflow(one, two, out)
+# endif
+
+/* Use Microsoft's safe integer handling functions where available */
+#elif defined(_MSC_VER)
+
+# define ENABLE_INTSAFE_SIGNED_FUNCTIONS
+# include <intsafe.h>
+
+# define git__add_sizet_overflow(out, one, two) \
+    (SizeTAdd(one, two, out) != S_OK)
+# define git__multiply_sizet_overflow(out, one, two) \
+    (SizeTMult(one, two, out) != S_OK)
+
+#define git__add_int_overflow(out, one, two) \
+    (IntAdd(one, two, out) != S_OK)
+#define git__sub_int_overflow(out, one, two) \
+    (IntSub(one, two, out) != S_OK)
+
+#define git__add_int64_overflow(out, one, two) \
+    (LongLongAdd(one, two, out) != S_OK)
+#define git__multiply_int64_overflow(out, one, two) \
+    (LongLongMult(one, two, out) != S_OK)
+
+#else
+
+/**
+ * Sets `one + two` into `out`, unless the arithmetic would overflow.
+ * @return false if the result fits in a `size_t`, true 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 false if the result fits in a `size_t`, true 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;
+}
+
+GIT_INLINE(bool) git__add_int_overflow(int *out, int one, int two)
+{
+	if ((two > 0 && one > (INT_MAX - two)) ||
+	    (two < 0 && one < (INT_MIN - two)))
+		return true;
+	*out = one + two;
+	return false;
+}
+
+GIT_INLINE(bool) git__sub_int_overflow(int *out, int one, int two)
+{
+	if ((two > 0 && one < (INT_MIN + two)) ||
+	    (two < 0 && one > (INT_MAX + two)))
+		return true;
+	*out = one - two;
+	return false;
+}
+
+GIT_INLINE(bool) git__add_int64_overflow(int64_t *out, int64_t one, int64_t two)
+{
+	if ((two > 0 && one > (INT64_MAX - two)) ||
+	    (two < 0 && one < (INT64_MIN - two)))
+		return true;
+	*out = one + two;
+	return false;
+}
+
+#endif
+
+/* If we could not provide an intrinsic implementation for this, provide a (slow) fallback. */
+#if !defined(git__multiply_int64_overflow)
+GIT_INLINE(bool) git__multiply_int64_overflow(int64_t *out, int64_t one, int64_t two)
+{
+	/*
+	 * Detects whether `INT64_MAX < (one * two) || INT64_MIN > (one * two)`,
+	 * without incurring in undefined behavior. That is done by performing the
+	 * comparison with a division instead of a multiplication, which translates
+	 * to `INT64_MAX / one < two || INT64_MIN / one > two`. Some caveats:
+	 *
+	 * - The comparison sign is inverted when both sides of the inequality are
+	 *   multiplied/divided by a negative number, so if `one < 0` the comparison
+	 *   needs to be flipped.
+	 * - `INT64_MAX / -1` itself overflows (or traps), so that case should be
+	 *   avoided.
+	 * - Since the overflow flag is defined as the discrepance between the result
+	 *   of performing the multiplication in a signed integer at twice the width
+	 *   of the operands, and the truncated+sign-extended version of that same
+	 *   result, there are four cases where the result is the opposite of what
+	 *   would be expected:
+	 *   * `INT64_MIN * -1` / `-1 * INT64_MIN`
+	 *   * `INT64_MIN * 1 / `1 * INT64_MIN`
+	 */
+	if (one && two) {
+		if (one > 0 && two > 0) {
+			if (INT64_MAX / one < two)
+				return true;
+		} else if (one < 0 && two < 0) {
+			if ((one == -1 && two == INT64_MIN) ||
+				  (two == -1 && one == INT64_MIN)) {
+				*out = INT64_MIN;
+				return false;
+			}
+			if (INT64_MAX / one > two)
+				return true;
+		} else if (one > 0 && two < 0) {
+			if ((one == 1 && two == INT64_MIN) ||
+			    (INT64_MIN / one > two))
+				return true;
+		} else if (one == -1) {
+			if (INT64_MIN / two > one)
+				return true;
+		} else {
+			if ((one == INT64_MIN && two == 1) ||
+			    (INT64_MIN / one < two))
+				return true;
+		}
+	}
+	*out = one * two;
+	return false;
+}
+#endif
+
+#endif