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    // Copyright 2015-2016 Brian Smith.
    //
    // Permission to use, copy, modify, and/or distribute this software for any
    // purpose with or without fee is hereby granted, provided that the above
    // copyright notice and this permission notice appear in all copies.
    //
    // THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHORS DISCLAIM ALL WARRANTIES
    // WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    // MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
    // SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    // WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
    // OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
    // CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

    //! TODO: Module-level documentation.

    #![allow(non_camel_case_types)]

    macro_rules! define_type {
        ( $name:ident, $builtin:ty, $test_c_metrics:ident, $get_c_align_fn:ident,
          $get_c_size_fn:ident, $doc:expr ) =>
        {
            #[allow(dead_code)] // Not all types are used in all configurations.
            #[doc = $doc]
            pub type $name = $builtin;

            define_metrics_tests!($name, $test_c_metrics, $get_c_align_fn,
                                  $get_c_size_fn);
        }
    }

    macro_rules! define_metrics_tests {
        ( $name:ident, $test_c_metrics:ident, $get_c_align_fn:ident,
          $get_c_size_fn:ident ) =>
        {
            define_metrics_tests!($name, $test_c_metrics, $get_c_align_fn,
                                  $get_c_size_fn, 1);
        };

        ( $name:ident, $test_c_metrics:ident, $c_align:ident, $c_size:ident,
          $expected_align_factor:expr ) =>
        {
            #[cfg(test)]
            extern {
                // We can't use `size_t` because we need to test that our
                // definition of `size_t` is correct using this code! We use `u16`
                // because even 8-bit and 16-bit microcontrollers have no trouble
                // with it, and because `u16` is always as smaller or smaller than
                // `usize`.
                static $c_align: u16;
                static $c_size: u16;
            }

            #[cfg(test)]
            #[test]
            fn $test_c_metrics() {
                use std::mem;

                let c_align = unsafe { $c_align };
                let c_size = unsafe { $c_size };

                // XXX: Remove these assertions and these uses of `as` when Rust
                // supports implicit coercion of `u16` to `usize`.
                assert!(mem::size_of_val(&c_align) <= mem::size_of::<usize>());
                assert!(mem::size_of_val(&c_size) <= mem::size_of::<usize>());

                // Rust uses 4 for the alignment of `i64` and `u64`. On Linux x86,
                // GCC 5 uses 8 but earlier versions use 4 and so does Clang.
                let rust_align =
                    if $expected_align_factor != 1 &&
                       mem::align_of::<$name>() != c_align as usize {
                       mem::align_of::<$name>() * $expected_align_factor
                    } else {
                        mem::align_of::<$name>()
                    };

                assert_eq!((rust_align, mem::size_of::<$name>()),
                           (c_align as usize, c_size as usize));
            }
        }
    }

    define_type!(int, i32, test_int_metrics, GFp_int_align, GFp_int_size,
                 "The C `int` type. Equivalent to `libc::c_int`.");

    define_type!(uint, u32, test_uint_metrics, GFp_uint_align, GFp_uint_size,
                 "The C `unsigned int` type. Equivalent to `libc::c_uint`.");

    #[cfg(any(target_os = "windows", target_pointer_width = "32"))]
    define_type!(long, i32, test_long_metrics, GFp_long_align, GFp_long_size,
                 "The C `long` type. Equivalent to `libc::c_long`.");

    #[cfg(not(any(target_os = "windows", target_pointer_width = "32")))]
    define_type!(long, i64, test_long_metrics, GFp_long_align, GFp_long_size,
                 "The C `long` type. Equivalent to `libc::c_long`.");

    define_type!(
      size_t, usize, test_size_t_metrics, GFp_size_t_align, GFp_size_t_size,
      "The C `size_t` type from `<stdint.h>`.

      ISO C's `size_t` is defined to be the type of the result of the
      `sizeof` operator and the type of the size parameter to `malloc`. That
      is, C's `size_t` is only required to hold the size of the largest object
      that can be allocated. In particular, it is legal for a C implementation
      to have a maximum object size smaller than the entire address space. For
      example, a C implementation may have an maximum object size of 2^32
      bytes with a 64-bit address space, and typedef `size_t` as `uint32_t` so
      that `sizeof(size_t) == 4` and `sizeof(void*) == 8`.

      Rust's `usize`, on the other hand, is defined to always be the same size
      as a pointer. This means that it is possible, in theory, to have a platform
      where `usize` can represent values that `size_t` cannot represent. However,
      on the vast majority of systems, `usize` and `size_t` are represented the
      same way. If it were required to explicitly cast `usize` to `size_t` on
      common platforms, then many programmers would habitually write expressions
      such as `my_slice.len() as libc::size_t` expecting this to always work and
      be safe. But such a cast is *not* safe on the uncommon platforms where
      `mem::sizeof(libc::size_t) < mem::size_t(usize)`. Consequently, to reduce
      the chances of programmers becoming habituated to such casts that would be
      unsafe on unusual platforms, we have adopted the following convention:

      * On common platforms where C's `size_t` is the same size as `usize`,
        `ring::c::size_t` must be a type alias of `usize`.

      * On uncommon platforms where C's `size_t` is not the same size as `usize`,
        `ring::c::size_t` must be a type alias for a type other than `usize`.

      * Code that was written without consideration for the uncommon platforms
        should not do any explicit casting between `size_t` and `usize`. Such
        code will fail to compile on the uncommon platforms; this is better than
        executing with unsafe truncations.

      * Code that was written with full consideration of the uncommon platforms
        should have explicit casts using `num::cast` or other methods that avoid
        unintended truncation. Such code will then work on all platforms.");

    define_metrics_tests!(i8, test_i8_metrics, GFp_int8_t_align, GFp_int8_t_size);
    define_metrics_tests!(u8, test_u8_metrics, GFp_uint8_t_align,
                          GFp_uint8_t_size);

    define_metrics_tests!(i16, test_i16_metrics, GFp_int16_t_align,
                          GFp_int16_t_size);
    define_metrics_tests!(u16, test_u16_metrics, GFp_uint16_t_align,
                          GFp_uint16_t_size);

    define_metrics_tests!(i32, test_i32_metrics, GFp_int32_t_align,
                          GFp_int32_t_size);
    define_metrics_tests!(u32, test_u32_metrics, GFp_uint32_t_align,
                          GFp_uint32_t_size);

    #[cfg(all(test, not(any(
                all(target_arch = "x86", target_os = "linux"),
                all(target_arch = "x86", target_os = "macos"),
                all(target_arch = "x86", target_os = "ios"),
                all(target_arch = "arm", target_os = "ios")
    ))))]
    const SIXTY_FOUR_BIT_ALIGNMENT_FACTOR: usize = 1;

    #[cfg(all(test, any(
                all(target_arch = "x86", target_os = "linux"),
                all(target_arch = "x86", target_os = "macos"),
                all(target_arch = "x86", target_os = "ios"),
                all(target_arch = "arm", target_os = "ios")
    )))]
    const SIXTY_FOUR_BIT_ALIGNMENT_FACTOR: usize = 2;

    define_metrics_tests!(i64, test_i64_metrics, GFp_int64_t_align,
                          GFp_int64_t_size, SIXTY_FOUR_BIT_ALIGNMENT_FACTOR);
    define_metrics_tests!(u64, test_u64_metrics, GFp_uint64_t_align,
                          GFp_uint64_t_size, SIXTY_FOUR_BIT_ALIGNMENT_FACTOR);

    #[cfg(target_os = "windows")]
    #[allow(non_snake_case)]
    pub mod win32 {
        define_type!(ULONG, u32, test_ULONG_metrics, GFp_ULONG_align,
                    GFp_ULONG_size, "The win32 `ULONG` type.");
        define_type!(BOOLEAN, u8, test_BOOLEAN_metrics, GFp_BOOLEAN_align,
                    GFp_BOOLEAN_size, "The win32 `BOOLEAN` type.");
    }

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