A single-file coroutine implementation in pure C

co.h

/**
 * Copyright (c) 2022 Chris Baker
 * 
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to
 * deal in the Software without restriction, including without limitation the
 * rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
 * sell copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 * 
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 **/

#ifndef __CO_H__
#define __CO_H__

#ifdef __cplusplus
extern "C" {
#endif

typedef unsigned int co_t;

#define co_init(co) ((*(co)) = 0)

#define co_routine(co) \
  switch (*(co)) \
    case 0: \
      if ((*(co) = -1))

#define co_yield(co) \
  if (!(*(co) = __LINE__)) { \
    case __LINE__: \
    *(co) = -1; \
  } else if (*(co) == __LINE__)

#ifdef __cplusplus
}
#endif

#ifdef CO_TEST

#include "mocha.h"

static void co_test_return_void(co_t *co, int *out) {
  co_routine(co) {
    /* single-statement yield */
    *out = 0;
    co_yield(co) return;

    /* multi-statement yield */
    co_yield(co) {
      *out = 1;
      return;
    }
  }

  *out = 2;
  return;
}

static int co_test_return_int(co_t *co) {
  co_routine(co) {
    co_yield(co) return 0;
    co_yield(co) return 1;
  }

  return 2;
}

static void co_test(mocha_t *mocha) {
  co_t co;

  mocha_describe(mocha, "co") {
    mocha_before_each(mocha) {
      co_init(&co);
    }

    mocha_after_each(mocha) {
      /* no cleanup */
    }

    mocha_it(mocha, "can yield return void") {
      int out;

      co_test_return_void(&co, &out);
      mocha_assert(mocha, out == 0);

      co_test_return_void(&co, &out);
      mocha_assert(mocha, out == 1);

      co_test_return_void(&co, &out);
      mocha_assert(mocha, out == 2);

      co_test_return_void(&co, &out);
      mocha_assert(mocha, out == 2);
    }

    mocha_it(mocha, "can yield return a value") {
      mocha_assert(mocha, co_test_return_int(&co) == 0);
      mocha_assert(mocha, co_test_return_int(&co) == 1);
      mocha_assert(mocha, co_test_return_int(&co) == 2);
      mocha_assert(mocha, co_test_return_int(&co) == 2);
    }
  }
}

#endif /* CO_TEST */
#endif /* __CO_H__ */