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/* 
|| This file is part of Pike. For copyright information see COPYRIGHT. 
|| Pike is distributed under GPL, LGPL and MPL. See the file COPYING 
|| for more information. 
*/ 
 
#include "global.h" 
#include "cyclic.h" 
 
#define CYCLIC_HASH_SIZE 0x1000 
 
static CYCLIC *cyclic_hash[CYCLIC_HASH_SIZE]; 
 
static size_t cyclic_hash_func(CYCLIC *c) 
{ 
  size_t h; 
 
  h = PTR_TO_INT(c->id); 
  h *= 33; 
  h ^= PTR_TO_INT(c->a); 
  h *= 33; 
  h ^= PTR_TO_INT(c->b); 
  h *= 33; 
  h ^= PTR_TO_INT(c->th); 
 
#if SIZEOF_CHAR_P > 4 
  h ^= h>>8; 
#endif 
  /* Fold h. This is to retain as many bits of h as possible. 
   * 
   * NB: The "magic" constant below has a 1 bit every 10 bits 
   *     starting at the least significant, and is == 1 when 
   *     shifted right 20 bits. Note also that 32 - 20 == 12 
   *     and 1<<12 == 0x1000 == CYCLIC_HASH_SIZE. 
   * 
   *     The multiplication has the effect of accumulating 
   *     the segments of 10 bits of h in the most significant 
   *     segment, which is then shifted down. 
   */ 
  h *= 0x100401; 
  h >>= 20; 
 
  return h & (CYCLIC_HASH_SIZE-1); 
} 
 
static void low_unlink_cyclic(CYCLIC *c) 
{ 
  size_t h; 
  CYCLIC **p; 
 
  h = cyclic_hash_func(c); 
 
  for(p=cyclic_hash+h;*p;p=&(p[0]->next)) 
  { 
    if(c == *p) 
    { 
      *p=c->next; 
#ifdef CYCLIC_DEBUG 
      fprintf (stderr, "%s: END_CYCLIC a=%p b=%p: no cycle\n", c->id, c->a, c->b); 
#endif 
      return; 
    } 
  } 
#ifdef PIKE_DEBUG 
  Pike_fatal("Unlink cyclic on lost cyclic struct (%s).\n", c->id); 
#else 
  Pike_fatal("Unlink cyclic on lost cyclic struct.\n"); 
#endif 
} 
 
PMOD_EXPORT void unlink_cyclic(CYCLIC *c) 
{ 
  UNSET_ONERROR(c->onerr); 
  low_unlink_cyclic(c); 
} 
 
PMOD_EXPORT void *begin_cyclic(CYCLIC *c, 
                               char *id, 
                               void *th, 
                               void *a, 
                               void *b) 
{ 
  size_t h; 
  void *ret = 0; 
  CYCLIC *p; 
 
  c->ret = (void *)(ptrdiff_t)1; 
  c->a = a; 
  c->b = b; 
  c->id = id; 
  c->th = th; 
 
  h = cyclic_hash_func(c); 
 
  for(p=cyclic_hash[h];p;p=p->next) 
  { 
    if(a == p->a && b==p->b && id==p->id && th==p->th) 
    { 
#ifdef CYCLIC_DEBUG 
      fprintf (stderr, "%s: BEGIN_CYCLIC a=%p b=%p: found cycle\n", id, a, b); 
#endif 
      c->ret = ret = p->ret; 
      break; 
    } 
  } 
 
  c->next = cyclic_hash[h]; 
  cyclic_hash[h] = c; 
  SET_ONERROR(c->onerr, low_unlink_cyclic, c); 
#ifdef CYCLIC_DEBUG 
  if (!ret) fprintf (stderr, "%s: BEGIN_CYCLIC a=%p b=%p: no cycle\n", id, a, b); 
#endif 
  return ret; 
}