#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdarg.h>
#include <time.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <string.h>


#define FILENAME      "Areas"

#define MAPW  800
#define MAPH  720
#define FASTCOLUMNS


typedef int int32;

typedef struct {
  int32 width, height;
  int32 next_x, next_y;
} header_t;


unsigned char map[MAPH*MAPW];
unsigned char *Data;
header_t *header;
double scale;


void Error(char *msg)
{
  fprintf(stderr, "%s\n", msg);
  exit(1);
}


void openmap(const char *filename)
{
  int Data_fd = open(filename, O_RDONLY);
  off_t Data_length;
  if (Data_fd == -1)
    Error("open failed");
  Data_length = lseek(Data_fd, 0, SEEK_END);
  fprintf(stderr, "%ld bytes\n", (long) Data_length);
  lseek(Data_fd, 0, SEEK_SET);
  Data = mmap(NULL, Data_length,
              PROT_READ,
              MAP_SHARED, Data_fd, 0);
  if (Data == MAP_FAILED)
    Error("mmap failed");
#ifndef FASTCOLUMNS
  if (madvise(Data, Data_length, MADV_SEQUENTIAL) < 0)
    perror("madvise warning");
#endif

  header = (header_t*) Data;
  double scale1 = (MAPW-0.5) / (header->width * 5);
  double scale2 = (MAPH-0.5) / header->height;
  if (scale1 < scale2)
    scale = scale1;
  else
    scale = scale2;
  fprintf(stderr, "scaling down %.1f times\n", 1.0 / scale);
}

void processmap(void)
{
  int width = header->width;
  int height = header->height;
  int x, y, i;
  unsigned char *p = Data + height;
  unsigned char *mapcolumn, *prevcol;
  double dx = 0.0;
  double dy;

  memset(map, 255, sizeof(map));
  x = ((int)(width * scale * 5.0)) - 1;
  for (y=0; y<MAPH; y++)
    {
      map[y] = 192;
      map[x * MAPH + y] = 192;
    }
  for (i=1; i<width; i++)
    {
      long PAGESIZE = 4096;
      long offset = i * (long) height;
      offset &= ~(PAGESIZE-1);
      x = offset / height - 1;
      y = offset % height;
      if (x >= 0 && y > 0)
        {
          int mx = (int) x * scale * 5.0;
          int my = (int) y * scale;
          while (my < MAPH)
            {
              map[mx * MAPH + my] = 192;
              my++;
            }
        }
      offset += PAGESIZE - 1;
      x = offset / height - 1;
      y = offset % height;
      if (1)
        {
          int mx = (int) x * scale * 5.0;
          int my = (int) y * scale;
          while (my >= 0)
            {
              map[mx * MAPH + my] = 192;
              my--;
            }
        }
    }
  prevcol = NULL;
  for (x=1; x<width; x++)
    {
      dx += scale * 5.0;
      mapcolumn = map + ((int) dx) * MAPH;
#ifdef FASTCOLUMNS
      if (mapcolumn == prevcol)
        {
          p += height;
          continue;
        }
#endif
      prevcol = mapcolumn;
      dy = 0.0;
      for (y=0; y<height; y++)
        {
          int c = *p++;
          if (c)
            mapcolumn[(int) dy] += c;
          dy += scale;
        }
    }
}

void outputpgm(void)
{
  unsigned char line[MAPW];
  int x, y;
  int mapw = (int)(header->width * scale * 5.0);
  int maph = (int)(header->height * scale);
  printf("P5\n");
  printf("%d %d\n", mapw, maph);
  printf("255\n");
  for (y=0; y<maph; y++)
    {
      for (x=0; x<mapw; x++)
        line[x] = map[y+x*MAPH];
      if (fwrite(line, mapw, 1, stdout) != 1)
        Error("fwrite error");
    }
}


int main(int argc, char* argv[])
{
  const char *filename;
  if (argc > 1)
    filename = argv[1];
  else
    filename = FILENAME;
  openmap(filename);
  processmap();
  outputpgm();
  return 0;
}