[libc++][C++17] Elementary string conversions for integral types

Summary:
Major QoI considerations:

- The facility is backported to C++14, same as libstdc++.
- Efforts have been made to minimize the header dependencies.
- The design is friendly to the uses of MSVC intrinsics (`__emulu`, `_umul128`, `_BitScanForward`, `_BitScanForward64`) but not implemented; future contributions are welcome.

Thanks to Milo Yip for contributing the implementation of `__u64toa` and `__u32toa`.

References:
 https://wg21.link/p0067r5
 https://wg21.link/p0682r1

Reviewers: mclow.lists, EricWF

Reviewed By: mclow.lists

Subscribers: ldionne, Quuxplusone, christof, mgorny, cfe-commits

Differential Revision: https://reviews.llvm.org/D41458

llvm-svn: 338479

1 files changed, 80 insertions, 0 deletions

diff --git a/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp b/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp
new file mode 100644
index 00000000000..50ca5b1906e
--- /dev/null
+++ b/libcxx/test/std/utilities/charconv/charconv.to.chars/integral.pass.cpp
@@ -0,0 +1,80 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++98, c++03, c++11
+// <charconv>
+
+// to_chars_result to_chars(char* first, char* last, Integral value,
+//                          int base = 10)
+
+#include "charconv_test_helpers.h"
+
+template <typename T>
+struct test_basics : to_chars_test_base<T>
+{
+    using to_chars_test_base<T>::test;
+    using to_chars_test_base<T>::test_value;
+
+    void operator()()
+    {
+        test(0, "0");
+        test(42, "42");
+        test(32768, "32768");
+        test(0, "0", 10);
+        test(42, "42", 10);
+        test(32768, "32768", 10);
+        test(0xf, "f", 16);
+        test(0xdeadbeaf, "deadbeaf", 16);
+        test(0755, "755", 8);
+
+        for (int b = 2; b < 37; ++b)
+        {
+            using xl = std::numeric_limits<T>;
+
+            test_value(1, b);
+            test_value(xl::lowest(), b);
+            test_value((xl::max)(), b);
+            test_value((xl::max)() / 2, b);
+        }
+    }
+};
+
+template <typename T>
+struct test_signed : to_chars_test_base<T>
+{
+    using to_chars_test_base<T>::test;
+    using to_chars_test_base<T>::test_value;
+
+    void operator()()
+    {
+        test(-1, "-1");
+        test(-12, "-12");
+        test(-1, "-1", 10);
+        test(-12, "-12", 10);
+        test(-21734634, "-21734634", 10);
+        test(-2647, "-101001010111", 2);
+        test(-0xcc1, "-cc1", 16);
+
+        for (int b = 2; b < 37; ++b)
+        {
+            using xl = std::numeric_limits<T>;
+
+            test_value(0, b);
+            test_value(xl::lowest(), b);
+            test_value((xl::max)(), b);
+        }
+    }
+};
+
+int
+main()
+{
+    run<test_basics>(integrals);
+    run<test_signed>(all_signed);
+}