intx: Add as_bytes() helper for casting intx to bytes

Author: chfast

include/intx/intx.hpp

@@ -434,6 +434,18 @@ constexpr const uint64_t* as_words(const uint<N>& x) noexcept
     return as_words(x.lo);
 }
 
+template <unsigned N>
+inline uint8_t* as_bytes(uint<N>& x) noexcept
+{
+    return reinterpret_cast<uint8_t*>(as_words(x));
+}
+
+template <unsigned N>
+inline const uint8_t* as_bytes(const uint<N>& x) noexcept
+{
+    return reinterpret_cast<const uint8_t*>(as_words(x));
+}
+
 /// Implementation of shift left as a loop.
 /// This one is slower than the one using "split" strategy.
 template <unsigned N>

test/unittests/test_intx.cpp

@@ -490,4 +490,18 @@ TYPED_TEST(uint_test, to_string_base)
     EXPECT_EQ(to_string(x, 36), "sg");
     EXPECT_EQ(to_string(x, 2), "10000000000");
     EXPECT_EQ(to_string(x, 8), "2000");
-}
+}
+
+TYPED_TEST(uint_test, as_bytes)
+{
+    constexpr auto x = TypeParam{0xa05};
+    const auto b = as_bytes(x);
+    EXPECT_EQ(b[0], 5);
+    EXPECT_EQ(b[1], 0xa);
+
+    auto y = x;
+    auto d = as_bytes(y);
+    d[0] = 3;
+    d[1] = 0xc;
+    EXPECT_EQ(y, 0xc03);
+}