Add support for 0X prefix to from_string()

Author: chfast

include/intx/intx.hpp

@@ -813,7 +813,7 @@ constexpr Int from_string(const char* str)
     auto x = Int{};
     int num_digits = 0;
 
-    if (s[0] == '0' && s[1] == 'x')
+    if (s[0] == '0' && (s[1] == 'x' || s[1] == 'X'))
     {
         s += 2;
         while (const auto c = *s++)

test/unittests/test_int128.cpp

@@ -392,16 +392,26 @@ TEST(int128, literals)
 
 TEST(int128, from_string)
 {
-    constexpr auto ka = from_string<uint128>("18446744073709551617");
-    static_assert(ka == uint128{1, 1});
-    const auto* const sa = "18446744073709551617";
-    const auto a = from_string<uint128>(sa);
-    EXPECT_EQ(a, uint128(1, 1));
-
-    constexpr auto kb = from_string<uint128>("0x300aabbccddeeff99");
-    static_assert(kb == uint128{0xaabbccddeeff99, 3});
-    const auto* const sb = "0x300aabbccddeeff99";
-    EXPECT_EQ(from_string<uint128>(sb), uint128(0xaabbccddeeff99, 3));
+    {
+        constexpr auto k = from_string<uint128>("18446744073709551617");
+        static_assert(k == uint128{1, 1});
+        const auto* const s = "18446744073709551617";
+        EXPECT_EQ(from_string<uint128>(s), uint128(1, 1));
+    }
+
+    {
+        constexpr auto k = from_string<uint128>("0x300aabbccddeeff99");
+        static_assert(k == uint128{0xaabbccddeeff99, 3});
+        const auto* const s = "0x300aabbccddeeff99";
+        EXPECT_EQ(from_string<uint128>(s), uint128(0xaabbccddeeff99, 3));
+    }
+
+    {
+        constexpr auto k = from_string<uint128>("0X300AABBCCDDEEFF99");
+        static_assert(k == uint128{0xaabbccddeeff99, 3});
+        const auto* const s = "0X300AABBCCDDEEFF99";
+        EXPECT_EQ(from_string<uint128>(s), uint128(0xaabbccddeeff99, 3));
+    }
 }
 
 TEST(int128, from_string_exceptions)