#include <zebra.h>
#include <stdlib.h>
#include <time.h>

#include "checksum.h"

struct thread_master *master;

struct acc_vals {
  int c0;
  int c1;
};

struct csum_vals {
  struct acc_vals a;
  int x; 
  int y;
};

static struct csum_vals ospfd_vals, isisd_vals;

typedef size_t testsz_t;
typedef uint16_t testoff_t;

/* Fletcher Checksum -- Refer to RFC1008. */
#define MODX                 4102

/* Accumulator phase of checksum */
static 
struct acc_vals
accumulate (u_char *buffer, testsz_t len, testoff_t off)
{
  u_int8_t *p;
  u_int16_t *csum;
  int i, init_len, partial_len;
  struct acc_vals ret;
  
  csum = (u_int16_t *) (buffer + off);
  *(csum) = 0;
  
  p = buffer;
  ret.c0 = 0;
  ret.c1 = 0;
  init_len = len;
  
  while (len != 0)
    {
      partial_len = MIN(len, MODX);

      for (i = 0; i < partial_len; i++)
	{
	  ret.c0 = ret.c0 + *(p++);
	  ret.c1 += ret.c0;
	}

      ret.c0 = ret.c0 % 255;
      ret.c1 = ret.c1 % 255;

      len -= partial_len;
    }
  return ret;
}

/* The final reduction phase.
 * This one should be the original ospfd version 
 */
static u_int16_t 
reduce_ospfd (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1

  x = ((len - off - 1) * c0 - c1) % 255;
  
  if (x <= 0)
    x += 255;
  y = 510 - c0 - x;
  if (y > 255)
    y -= 255;

   /* take care endian issue. */
   return htons ((x << 8) + y); 
#undef x
#undef y
#undef c0
#undef c1
}

/* slightly different concatenation */
static u_int16_t 
reduce_ospfd1 (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1

  x = ((len - off - 1) * c0 - c1) % 255;
  if (x <= 0)
    x += 255;
  y = 510 - c0 - x;
  if (y > 255)
    y -= 255;

   /* take care endian issue. */
   return htons ((x << 8) | (y & 0xff)); 
#undef x
#undef y
#undef c0
#undef c1
}

/* original isisd version */
static u_int16_t 
reduce_isisd (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
  u_int32_t mul;
  
  mul = (len - off)*(c0);
  x = mul - c0 - c1;
  y = c1 - mul - 1;

  if (y > 0)
    y++;
  if (x < 0)
    x--;

  x %= 255;
  y %= 255;

  if (x == 0)
    x = 255;
  if (y == 0)
    y = 1;

  return htons ((x << 8) | (y & 0xff));

#undef x
#undef y
#undef c0
#undef c1
}

/* Is the -1 in y wrong perhaps? */
static u_int16_t 
reduce_isisd_yfix (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
  u_int32_t mul;
  
  mul = (len - off)*(c0);
  x = mul - c0 - c1;
  y = c1 - mul;

  if (y > 0)
    y++;
  if (x < 0)
    x--;

  x %= 255;
  y %= 255;

  if (x == 0)
    x = 255;
  if (y == 0)
    y = 1;

  return htons ((x << 8) | (y & 0xff));

#undef x
#undef y
#undef c0
#undef c1
}

/* Move the mods yp */
static u_int16_t 
reduce_isisd_mod (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
  u_int32_t mul;
  
  mul = (len - off)*(c0);
  x = mul - c1 - c0;
  y = c1 - mul - 1;

  x %= 255;
  y %= 255;

  if (y > 0)
    y++;
  if (x < 0)
    x--;

  if (x == 0)
    x = 255;
  if (y == 0)
    y = 1;

  return htons ((x << 8) | (y & 0xff));

#undef x
#undef y
#undef c0
#undef c1
}

/* Move the mods up + fix y */
static u_int16_t 
reduce_isisd_mody (struct csum_vals *vals, testsz_t len, testoff_t off)
{
#define x vals->x
#define y vals->y
#define c0 vals->a.c0
#define c1 vals->a.c1
  u_int32_t mul;
  
  mul = (len - off)*(c0);
  x = mul - c0 - c1;
  y = c1 - mul;

  x %= 255;
  y %= 255;

  if (y > 0)
    y++;
  if (x < 0)
    x--;

  if (x == 0)
    x = 255;
  if (y == 0)
    y = 1;

  return htons ((x << 8) | (y & 0xff));

#undef x
#undef y
#undef c0
#undef c1
}

struct reductions_t {
  const char *name;
  u_int16_t (*f) (struct csum_vals *, testsz_t, testoff_t);
} reducts[] = {
  { .name = "ospfd",		.f = reduce_ospfd },
  { .name = "ospfd-1",		.f = reduce_ospfd1 },
  { .name = "isisd", 		.f = reduce_isisd },
  { .name = "isisd-yfix", 	.f = reduce_isisd_yfix },
  { .name = "isisd-mod", 	.f = reduce_isisd_mod },
  { .name = "isisd-mody", 	.f = reduce_isisd_mody },
  { NULL, NULL },
};

/* The original ospfd checksum */
static u_int16_t
ospfd_checksum (u_char *buffer, testsz_t len, testoff_t off)
{
  u_char *sp, *ep, *p, *q;
  int c0 = 0, c1 = 0;
  int x, y;
  u_int16_t checksum, *csum;

  csum = (u_int16_t *) (buffer + off);
  *(csum) = 0;
  
  sp = buffer;

  for (ep = sp + len; sp < ep; sp = q)
    {
      q = sp + MODX;
      if (q > ep)
        q = ep;
      for (p = sp; p < q; p++)
        {
          c0 += *p;
          c1 += c0;
        }
      c0 %= 255;
      c1 %= 255;
    }
  
  ospfd_vals.a.c0 = c0;
  ospfd_vals.a.c1 = c1;
  
  //printf ("%s: len %u, off %u, c0 %d, c1 %d\n",
  //        __func__, len, off, c0, c1);

  x = ((int)(len - off - 1) * (int)c0 - (int)c1) % 255;
  
  if (x <= 0)
    x += 255;
  y = 510 - c0 - x;
  if (y > 255)
    y -= 255;
  
  ospfd_vals.x = x;
  ospfd_vals.y = y;
  
  buffer[off] = x;
  buffer[off + 1] = y;
  
  /* take care endian issue. */
  checksum = htons ((x << 8) | (y & 0xff));

  return (checksum);
}

/* the original, broken isisd checksum */
static u_int16_t
iso_csum_create (u_char * buffer, testsz_t len, testoff_t off)
{

  u_int8_t *p;
  int x;
  int y;
  u_int32_t mul;
  u_int32_t c0;
  u_int32_t c1;
  u_int16_t checksum, *csum;
  int i, init_len, partial_len;

  checksum = 0;
  
  csum = (u_int16_t *) (buffer + off);
  *(csum) = checksum;
  
  p = buffer;
  c0 = 0;
  c1 = 0;
  init_len = len;
  
  while (len != 0)
    {
      partial_len = MIN(len, MODX);

      for (i = 0; i < partial_len; i++)
	{
	  c0 = c0 + *(p++);
	  c1 += c0;
	}

      c0 = c0 % 255;
      c1 = c1 % 255;

      len -= partial_len;
    }

  isisd_vals.a.c0 = c0;
  isisd_vals.a.c1 = c1;
  
  mul = (init_len - off) * c0;

  x = mul - c1 - c0;
  y = c1 - mul - 1;

  if (y > 0)
    y++;
  if (x < 0)
    x--;

  x %= 255;
  y %= 255;

  if (x == 0)
    x = 255;
  if (y == 0)
    y = 1;
  
  isisd_vals.x = x;
  isisd_vals.y = y;
  
  checksum = htons((x << 8) | (y & 0xFF));
  
  *(csum) = checksum;
  
  /* return the checksum for user usage */
  return checksum;
}

static int
verify (u_char * buffer, testsz_t len)
{
  u_int8_t *p;
  u_int32_t c0;
  u_int32_t c1;
  u_int16_t checksum;
  int i, partial_len;
 
  p = buffer;
  checksum = 0;

  c0 = 0;
  c1 = 0;

  while (len)
    {
      partial_len = MIN(len, 5803);

      for (i = 0; i < partial_len; i++)
        {
          c0 = c0 + *(p++);
          c1 += c0;
        }
      c0 = c0 % 255;
      c1 = c1 % 255;

      len -= partial_len;
    }

  if (c0 == 0 && c1 == 0)
    return 0;

  return 1;
}

int
main(int argc, char **argv)
{
/* 60017 65629 702179 */
#define MAXDATALEN 60017
#define BUFSIZE MAXDATALEN + sizeof(u_int16_t)
  u_char buffer[BUFSIZE];
  int exercise = 0;
#define EXERCISESTEP 257
  
  srandom (time (NULL));
  
  while (1) {
    u_int16_t ospfd, isisd, lib;
    
    exercise += EXERCISESTEP;
    exercise %= MAXDATALEN;
    
    for (int i = 0; i < exercise; i += sizeof (long int)) {
      long int rand = random ();
      
      for (int j = sizeof (long int); j > 0; j--)
        buffer[i + (sizeof (long int) - j)] = (rand >> (j * 8)) & 0xff;
    }
    
    ospfd = ospfd_checksum (buffer, exercise + sizeof(u_int16_t), exercise);
    if (verify (buffer, exercise + sizeof(u_int16_t)))
      printf ("verify: ospfd failed\n");
    isisd = iso_csum_create (buffer, exercise + sizeof(u_int16_t), exercise);
    if (verify (buffer, exercise + sizeof(u_int16_t)))
      printf ("verify: isisd failed\n");
    lib = fletcher_checksum (buffer, exercise + sizeof(u_int16_t), exercise);
    if (verify (buffer, exercise + sizeof(u_int16_t)))
      printf ("verify: lib failed\n");
    
    if (ospfd != lib) {
      printf ("Mismatch in values at size %u\n"
              "ospfd: 0x%04x\tc0: %d\tc1: %d\tx: %d\ty: %d\n"
              "isisd: 0x%04x\tc0: %d\tc1: %d\tx: %d\ty: %d\n"
              "lib: 0x%04x\n",
              exercise,
              ospfd, ospfd_vals.a.c0, ospfd_vals.a.c1, ospfd_vals.x, ospfd_vals.y,
              isisd, isisd_vals.a.c0, isisd_vals.a.c1, isisd_vals.x, isisd_vals.y,
              lib
              );
      
      /* Investigate reduction phase discrepencies */
      if (ospfd_vals.a.c0 == isisd_vals.a.c0
          && ospfd_vals.a.c1 == isisd_vals.a.c1) {
        printf ("\n");
        for (int i = 0; reducts[i].name != NULL; i++) {	
          ospfd = reducts[i].f (&ospfd_vals,
                                exercise + sizeof (u_int16_t),
                                exercise);
          printf ("%20s: x: %02x, y %02x, checksum 0x%04x\n",
                  reducts[i].name, ospfd_vals.x & 0xff, ospfd_vals.y & 0xff, ospfd);
        }
      }
              
      printf ("\n  u_char testdata [] = {\n  ");
      for (int i = 0; i < exercise; i++) {
        printf ("0x%02x,%s",
                buffer[i],
                (i + 1) % 8 ? " " : "\n  ");
      }
      printf ("\n}\n");
      exit (1);
    }
  }
}