1 files changed, 99 insertions, 0 deletions
diff --git a/gfx/skia/skia/include/private/SkTFitsIn.h b/gfx/skia/skia/include/private/SkTFitsIn.h
new file mode 100644
index 0000000000..a912f13e08
--- /dev/null
+++ b/gfx/skia/skia/include/private/SkTFitsIn.h
@@ -0,0 +1,99 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkTFitsIn_DEFINED
+#define SkTFitsIn_DEFINED
+
+#include <limits>
+#include <stdint.h>
+#include <type_traits>
+
+/**
+ * std::underlying_type is only defined for enums. For integral types, we just want the type.
+ */
+template <typename T, class Enable = void>
+struct sk_strip_enum {
+    typedef T type;
+};
+
+template <typename T>
+struct sk_strip_enum<T, typename std::enable_if<std::is_enum<T>::value>::type> {
+    typedef typename std::underlying_type<T>::type type;
+};
+
+
+/**
+ * In C++ an unsigned to signed cast where the source value cannot be represented in the destination
+ * type results in an implementation defined destination value. Unlike C, C++ does not allow a trap.
+ * This makes "(S)(D)s == s" a possibly useful test. However, there are two cases where this is
+ * incorrect:
+ *
+ * when testing if a value of a smaller signed type can be represented in a larger unsigned type
+ * (int8_t)(uint16_t)-1 == -1 => (int8_t)0xFFFF == -1 => [implementation defined] == -1
+ *
+ * when testing if a value of a larger unsigned type can be represented in a smaller signed type
+ * (uint16_t)(int8_t)0xFFFF == 0xFFFF => (uint16_t)-1 == 0xFFFF => 0xFFFF == 0xFFFF => true.
+ *
+ * Consider the cases:
+ *   u = unsigned, less digits
+ *   U = unsigned, more digits
+ *   s = signed, less digits
+ *   S = signed, more digits
+ *   v is the value we're considering.
+ *
+ * u -> U: (u)(U)v == v, trivially true
+ * U -> u: (U)(u)v == v, both casts well defined, test works
+ * s -> S: (s)(S)v == v, trivially true
+ * S -> s: (S)(s)v == v, first cast implementation value, second cast defined, test works
+ * s -> U: (s)(U)v == v, *this is bad*, the second cast results in implementation defined value
+ * S -> u: (S)(u)v == v, the second cast is required to prevent promotion of rhs to unsigned
+ * u -> S: (u)(S)v == v, trivially true
+ * U -> s: (U)(s)v == v, *this is bad*,
+ *                             first cast results in implementation defined value,
+ *                             second cast is defined. However, this creates false positives
+ *                             uint16_t x = 0xFFFF
+ *                                (uint16_t)(int8_t)x == x
+ *                             => (uint16_t)-1        == x
+ *                             => 0xFFFF              == x
+ *                             => true
+ *
+ * So for the eight cases three are trivially true, three more are valid casts, and two are special.
+ * The two 'full' checks which otherwise require two comparisons are valid cast checks.
+ * The two remaining checks s -> U [v >= 0] and U -> s [v <= max(s)] can be done with one op.
+ */
+
+template <typename D, typename S>
+static constexpr inline
+typename std::enable_if<(std::is_integral<S>::value || std::is_enum<S>::value) &&
+                        (std::is_integral<D>::value || std::is_enum<D>::value), bool>::type
+/*bool*/ SkTFitsIn(S src) {
+    // SkTFitsIn() is used in public headers, so needs to be written targeting at most C++11.
+    return
+
+    // E.g. (int8_t)(uint8_t) int8_t(-1) == -1, but the uint8_t == 255, not -1.
+    (std::is_signed<S>::value && std::is_unsigned<D>::value && sizeof(S) <= sizeof(D)) ?
+        (S)0 <= src :
+
+    // E.g. (uint8_t)(int8_t) uint8_t(255) == 255, but the int8_t == -1.
+    (std::is_signed<D>::value && std::is_unsigned<S>::value && sizeof(D) <= sizeof(S)) ?
+        src <= (S)std::numeric_limits<typename sk_strip_enum<D>::type>::max() :
+
+#if !defined(SK_DEBUG) && !defined(__MSVC_RUNTIME_CHECKS )
+    // Correct (simple) version. This trips up MSVC's /RTCc run-time checking.
+    (S)(D)src == src;
+#else
+    // More complex version that's safe with /RTCc. Used in all debug builds, for coverage.
+    (std::is_signed<S>::value) ?
+        (intmax_t)src >= (intmax_t)std::numeric_limits<typename sk_strip_enum<D>::type>::min() &&
+        (intmax_t)src <= (intmax_t)std::numeric_limits<typename sk_strip_enum<D>::type>::max() :
+
+    // std::is_unsigned<S> ?
+        (uintmax_t)src <= (uintmax_t)std::numeric_limits<typename sk_strip_enum<D>::type>::max();
+#endif
+}
+
+#endif