Update documentation to add CUDA

Author: mborland

doc/charconv/api_reference.adoc

@@ -32,3 +32,4 @@ https://www.boost.org/LICENSE_1_0.txt
 
 - <<integral_usage_notes_, `BOOST_CHARCONV_CONSTEXPR`>>
 - <<run_benchmarks_, `BOOST_CHARCONV_RUN_BENCHMARKS`>>
+- <<host_device_, `BOOST_CHARCONV_HOST_DEVICE`>>

doc/charconv/from_chars.adoc

@@ -25,12 +25,12 @@ struct from_chars_result
     const char* ptr;
     std::errc ec;
 
-    friend constexpr bool operator==(const from_chars_result& lhs, const from_chars_result& rhs) noexcept = default;
-    constexpr explicit operator bool() const noexcept { return ec == std::errc{}; }
+    BOOST_CHARCONV_HOST_DEVICE friend constexpr bool operator==(const from_chars_result& lhs, const from_chars_result& rhs) noexcept = default;
+    BOOST_CHARCONV_HOST_DEVICE constexpr explicit operator bool() const noexcept { return ec == std::errc{}; }
 }
 
 template <typename Integral>
-BOOST_CXX14_CONSTEXPR from_chars_result from_chars(const char* first, const char* last, Integral& value, int base = 10) noexcept;
+BOOST_CHARCONV_HOST_DEVICE BOOST_CXX14_CONSTEXPR from_chars_result from_chars(const char* first, const char* last, Integral& value, int base = 10) noexcept;
 
 template <typename Integral>
 BOOST_CXX14_CONSTEXPR from_chars_result from_chars(boost::core::string_view sv, Integral& value, int base = 10) noexcept;
@@ -54,6 +54,12 @@ from_chars_result from_chars_erange(boost::core::string_view sv, Real& value, ch
 }} // Namespace boost::charconv
 ----
 
+[#host_device_]
+== `BOOST_CHARCONV_HOST_DEVICE`
+
+When compiling the library with NVCC, functions marked `BOOST_CHARCONV_HOST_DEVICE` expands to `pass:[__host__ __device__]` for use on both CPU and GPU.
+Otherwise `BOOST_CHARCONV_HOST_DEVICE` expands to the empty string.
+
 == from_chars parameters
 * `first`, `last` - pointers to a valid range to parse
 * `sv` - string view of a valid range to parse.

doc/charconv/overview.adoc

@@ -15,9 +15,10 @@ Boost.Charconv converts character buffers to numbers, and numbers to character b
 It is a small library of two overloaded functions to do the heavy lifting, plus several supporting enums, structures, templates, and constants, with a particular focus on performance and consistency
 across the supported development environments.
 
-Why should I be interested in this Library? Charconv is locale-independent, non-allocating^1^, non-throwing and only requires a minimum of C++ 11.
+Why should I be interested in this Library? Charconv is locale-independent, non-allocating^1^, non-throwing and only requires a minimum of pass:[C++11].
 It provides functionality similar to that found in `std::printf` or `std::strtod` with <<benchmark_results_, substantial performance increases>>.
 This library can also be used in place of the standard library `<charconv>` if unavailable with your toolchain.
+The integer portion of the library can also be used on GPU with NVCC.
 Currently only https://en.cppreference.com/w/cpp/compiler_support/17.html[GCC 11+ and MSVC 19.24+] support both integer and floating-point conversions in their implementation of `<charconv>`. +
 If you are using either of those compilers, Boost.Charconv is at least as performant as `<charconv>`, and can be up to several times faster.
 See: <<Benchmarks>>
@@ -31,5 +32,6 @@ Boost.Charconv is tested on Ubuntu, macOS, and Windows with the following compil
 * GCC 5 or later
 * Clang 3.8 or later
 * Visual Studio 2015 (14.0) or later
+* NVCC 12.8 or later
 
 Tested on https://github.com/boostorg/charconv/actions[GitHub Actions] and https://drone.cpp.al/boostorg/charconv[Drone].

doc/charconv/to_chars.adoc

@@ -25,12 +25,12 @@ struct to_chars_result
     char* ptr;
     std::errc ec;
 
-    friend constexpr bool operator==(const to_chars_result& lhs, const to_chars_result& rhs) noexcept; = default;
-    constexpr explicit operator bool() const noexcept { return ec == std::errc{}; }
+    BOOST_CHARCONV_HOST_DEVICE friend constexpr bool operator==(const to_chars_result& lhs, const to_chars_result& rhs) noexcept; = default;
+    BOOST_CHARCONV_HOST_DEVICE constexpr explicit operator bool() const noexcept { return ec == std::errc{}; }
 };
 
 template <typename Integral>
-BOOST_CHARCONV_CONSTEXPR to_chars_result to_chars(char* first, char* last, Integral value, int base = 10) noexcept;
+BOOST_CHARCONV_HOST_DEVICE BOOST_CHARCONV_CONSTEXPR to_chars_result to_chars(char* first, char* last, Integral value, int base = 10) noexcept;
 
 template <typename Integral>
 BOOST_CHARCONV_CONSTEXPR to_chars_result to_chars<bool>(char* first, char* last, Integral value, int base) noexcept = delete;
@@ -71,6 +71,7 @@ See <<chars_format overview>> for description.
 ** compiled using `-std=c++14` or newer 
 ** using a compiler with `\__builtin_ is_constant_evaluated`
 * These functions have been tested to support `\__int128` and `unsigned __int128`
+* When compiling with NVCC, (e.g., `BOOST_CHARCONV_HOST_DEVICE` defined as `pass:[__host__ __device__]`), these functions are available for use on CPU and GPU.
 
 === Usage notes for to_chars for floating point types
 * The following will be returned when handling different values of `NaN`