/**
 * Lambda Functions in C Experiment
 * Hakson "Kerafyrm" Teh
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/**
 * Definition of function #1:
 */
int add( int x, int y )
{
  return x + y;
}
void dummyfunc1() {}
// We need to end with a dummy function so we can easily compute the size of
// the function by calculating the differences in addresses.

/**
 * Definition of function #2:
 */
int sumsquares( int x, int y )
{
  // Just for fun, we make this function bigger:
  int part1 = x * x;
  int part2 = y * y;
  return part1 + part2;
}
void dummyfunc2() {}

int subtract( int x, int y )
{
  return x - y;
}

/**
 * ENTRY POINT
 */
int main( int argc, char *argv[] )
{
  int a, b, c;
  // Stack buffer to hold the code:
  char lambda[5000];

  /**
   * Print statistics :)
   */
  printf( "         Addr of add func(): %lx\n", (unsigned long)add );
  printf( "       Addr of dummyfunc1(): %lx\n", (unsigned long)dummyfunc1 );

  printf( "  Addr of submquares func(): %lx\n", (unsigned long)sumsquares );
  printf( "       Addr of dummyfunc1(): %lx\n", (unsigned long)dummyfunc2 );
  printf( "             Addr of main(): %lx\n", (unsigned long)main );

  unsigned long function_add_size        = (long)dummyfunc1 - (long)add;
  unsigned long function_sumsquares_size = (long)dummyfunc2 - (long)sumsquares;
  printf( "        add() function size: %lu\n", function_add_size );
  printf( " sumsquares() function size: %lu\n", function_sumsquares_size );

  a = b = 0;
  printf( "Before calls to lambda function:\n");
  printf( " a = %d\n", a );
  printf( " b = %d\n", b );

  // Load the first "lambda function" and call it:
  memcpy( &lambda, (char*)add, function_add_size );
  a = ((int (*)(int, int)) lambda)(4, 5);

  // Load the second "lambda function" and call it:
  memcpy( &lambda, (char*)sumsquares, function_sumsquares_size );
  b = ((int (*)(int, int)) lambda)(4, 5);

  // Load the machine code for a function that takes two ints, subtracts them
  // and returns the result as an int:
  strcpy( lambda, "\x55\x89\xe5\x8b\x55\x0c\x8b\x45\x08\x29\xd0\x5d\xc3" );
  c = ((int (*)(int, int)) lambda)(10, 2);

  printf( "After calls to lambda function:\n");
  printf( " a = %d\n", a );
  printf( " b = %d\n", b );
  printf( " c = %d\n", c );

  return EXIT_SUCCESS;
}