bitmap.c

/* Functions to support general ended bitmaps.
   Copyright (C) 1997, 1998, 1999, 2000, 2001, 2003, 2004, 2005
   Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under
the terms of the GNU General Public License as published by the Free
Software Foundation; either version 2, or (at your option) any later
version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY
WARRANTY; without even the implied warranty of MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING.  If not, write to the Free
Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301, USA.  */

#include "config.h"
#include "system.h"
#include "coretypes.h"
#include "tm.h"
#include "rtl.h"
#include "flags.h"
#include "obstack.h"
#include "ggc.h"
#include "bitmap.h"

/* Global data */
bitmap_element bitmap_zero_bits;  /* An element of all zero bits.  */
bitmap_obstack bitmap_default_obstack;    /* The default bitmap obstack.  */
static GTY((deletable)) bitmap_element *bitmap_ggc_free; /* Freelist of
							    GC'd elements.  */

static void bitmap_elem_to_freelist (bitmap, bitmap_element *);
static void bitmap_element_free (bitmap, bitmap_element *);
static bitmap_element *bitmap_element_allocate (bitmap);
static int bitmap_element_zerop (bitmap_element *);
static void bitmap_element_link (bitmap, bitmap_element *);
static bitmap_element *bitmap_elt_insert_after (bitmap, bitmap_element *, unsigned int);
static void bitmap_elt_clear_from (bitmap, bitmap_element *);
static bitmap_element *bitmap_find_bit (bitmap, unsigned int);


/* Add ELEM to the appropriate freelist.  */
static inline void
bitmap_elem_to_freelist (bitmap head, bitmap_element *elt)
{
  bitmap_obstack *bit_obstack = head->obstack;
  
  elt->next = NULL;
  if (bit_obstack)
    {
      elt->prev = bit_obstack->elements;
      bit_obstack->elements = elt;
    }
  else
    {
      elt->prev = bitmap_ggc_free;
      bitmap_ggc_free = elt;
    }
}

/* Free a bitmap element.  Since these are allocated off the
   bitmap_obstack, "free" actually means "put onto the freelist".  */

static inline void
bitmap_element_free (bitmap head, bitmap_element *elt)
{
  bitmap_element *next = elt->next;
  bitmap_element *prev = elt->prev;

  if (prev)
    prev->next = next;

  if (next)
    next->prev = prev;

  if (head->first == elt)
    head->first = next;

  /* Since the first thing we try is to insert before current,
     make current the next entry in preference to the previous.  */
  if (head->current == elt)
    {
      head->current = next != 0 ? next : prev;
      if (head->current)
	head->indx = head->current->indx;
      else 
	head->indx = 0;
    }
  bitmap_elem_to_freelist (head, elt);
}

/* Allocate a bitmap element.  The bits are cleared, but nothing else is.  */

static inline bitmap_element *
bitmap_element_allocate (bitmap head)
{
  bitmap_element *element;
  bitmap_obstack *bit_obstack = head->obstack;
      
  if (bit_obstack)
    {
      element = bit_obstack->elements;
      
      if (element)
	/* Use up the inner list first before looking at the next
	   element of the outer list.  */
	if (element->next)
	  {
	    bit_obstack->elements = element->next;
	    bit_obstack->elements->prev = element->prev;
	  }
	else
	  /*  Inner list was just a singleton.  */
	  bit_obstack->elements = element->prev;
      else
	element = XOBNEW (&bit_obstack->obstack, bitmap_element);
    }
  else
    {
      element = bitmap_ggc_free;
      if (element)
	/* Use up the inner list first before looking at the next
	   element of the outer list.  */
	if (element->next)
	  {
	    bitmap_ggc_free = element->next;
	    bitmap_ggc_free->prev = element->prev;
	  }
	else
	  /*  Inner list was just a singleton.  */
	  bitmap_ggc_free = element->prev;
      else
	element = GGC_NEW (bitmap_element);
    }

  memset (element->bits, 0, sizeof (element->bits));

  return element;
}

/* Remove ELT and all following elements from bitmap HEAD.  */

void
bitmap_elt_clear_from (bitmap head, bitmap_element *elt)
{
  bitmap_element *prev;
  bitmap_obstack *bit_obstack = head->obstack;

  if (!elt) return;

  prev = elt->prev;
  if (prev)
    {
      prev->next = NULL;
      if (head->current->indx > prev->indx)
	{
	  head->current = prev;
	  head->indx = prev->indx;
	}
    } 
  else
    {
      head->first = NULL;
      head->current = NULL;
      head->indx = 0;
    }

  /* Put the entire list onto the free list in one operation. */ 
  if (bit_obstack)
    {
      elt->prev = bit_obstack->elements; 
      bit_obstack->elements = elt;
    }
  else
    {
      elt->prev = bitmap_ggc_free;
      bitmap_ggc_free = elt;
    }
}

/* Clear a bitmap by freeing the linked list.  */

inline void
bitmap_clear (bitmap head)
{
  if (head->first)
    bitmap_elt_clear_from (head, head->first);
}

/* Initialize a bitmap obstack.  If BIT_OBSTACK is NULL, initialize
   the default bitmap obstack.  */

void
bitmap_obstack_initialize (bitmap_obstack *bit_obstack)
{
  if (!bit_obstack)
    bit_obstack = &bitmap_default_obstack;

#if !defined(__GNUC__) || (__GNUC__ < 2)
#define __alignof__(type) 0
#endif

  bit_obstack->elements = NULL;
  bit_obstack->heads = NULL;
  obstack_specify_allocation (&bit_obstack->obstack, OBSTACK_CHUNK_SIZE,
			      __alignof__ (bitmap_element),
			      obstack_chunk_alloc,
			      obstack_chunk_free);
}

/* Release the memory from a bitmap obstack.  If BIT_OBSTACK is NULL,
   release the default bitmap obstack.  */

void
bitmap_obstack_release (bitmap_obstack *bit_obstack)
{
  if (!bit_obstack)
    bit_obstack = &bitmap_default_obstack;
  
  bit_obstack->elements = NULL;
  bit_obstack->heads = NULL;
  obstack_free (&bit_obstack->obstack, NULL);
}

/* Create a new bitmap on an obstack.  If BIT_OBSTACK is NULL, create
   it on the default bitmap obstack.  */

bitmap
bitmap_obstack_alloc (bitmap_obstack *bit_obstack)
{
  bitmap map;

  if (!bit_obstack)
    bit_obstack = &bitmap_default_obstack;
  map = bit_obstack->heads;
  if (map)
    bit_obstack->heads = (void *)map->first;
  else
    map = XOBNEW (&bit_obstack->obstack, bitmap_head);
  bitmap_initialize (map, bit_obstack);

  return map;
}

/* Create a new GCd bitmap.  */

bitmap
bitmap_gc_alloc (void)
{
  bitmap map;

  map = GGC_NEW (struct bitmap_head_def);
  bitmap_initialize (map, NULL);

  return map;
}

/* Release an obstack allocated bitmap.  */

void
bitmap_obstack_free (bitmap map)
{
  if (map)
    {
      bitmap_clear (map);
      map->first = (void *)map->obstack->heads;
      map->obstack->heads = map;
    }
}


/* Return nonzero if all bits in an element are zero.  */

static inline int
bitmap_element_zerop (bitmap_element *element)
{
#if BITMAP_ELEMENT_WORDS == 2
  return (element->bits[0] | element->bits[1]) == 0;
#else
  unsigned i;

  for (i = 0; i < BITMAP_ELEMENT_WORDS; i++)
    if (element->bits[i] != 0)
      return 0;

  return 1;
#endif
}

/* Link the bitmap element into the current bitmap linked list.  */

static inline void
bitmap_element_link (bitmap head, bitmap_element *element)
{
  unsigned int indx = element->indx;
  bitmap_element *ptr;

  /* If this is the first and only element, set it in.  */
  if (head->first == 0)
    {
      element->next = element->prev = 0;
      head->first = element;
    }

  /* If this index is less than that of the current element, it goes someplace
     before the current element.  */
  else if (indx < head->indx)
    {
      for (ptr = head->current;
	   ptr->prev != 0 && ptr->prev->indx > indx;
	   ptr = ptr->prev)
	;

      if (ptr->prev)
	ptr->prev->next = element;
      else
	head->first = element;

      element->prev = ptr->prev;
      element->next = ptr;
      ptr->prev = element;
    }

  /* Otherwise, it must go someplace after the current element.  */
  else
    {
      for (ptr = head->current;
	   ptr->next != 0 && ptr->next->indx < indx;
	   ptr = ptr->next)
	;

      if (ptr->next)
	ptr->next->prev = element;

      element->next = ptr->next;
      element->prev = ptr;
      ptr->next = element;
    }

  /* Set up so this is the first element searched.  */
  head->current = element;
  head->indx = indx;
}

/* Insert a new uninitialized element into bitmap HEAD after element
   ELT.  If ELT is NULL, insert the element at the start.  Return the
   new element.  */

static bitmap_element *
bitmap_elt_insert_after (bitmap head, bitmap_element *elt, unsigned int indx)
{
  bitmap_element *node = bitmap_element_allocate (head);
  node->indx = indx;

  if (!elt)
    {
      if (!head->current)
	{
	  head->current = node;
	  head->indx = indx;
	}
      node->next = head->first;
      if (node->next)
	node->next->prev = node;
      head->first = node;
      node->prev = NULL;
    }
  else
    {
      gcc_assert (head->current);
      node->next = elt->next;
      if (node->next)
	node->next->prev = node;
      elt->next = node;
      node->prev = elt;
    }
  return node;
}

/* Copy a bitmap to another bitmap.  */

void
bitmap_copy (bitmap to, bitmap from)
{
  bitmap_element *from_ptr, *to_ptr = 0;

  bitmap_clear (to);

  /* Copy elements in forward direction one at a time.  */
  for (from_ptr = from->first; from_ptr; from_ptr = from_ptr->next)
    {
      bitmap_element *to_elt = bitmap_element_allocate (to);

      to_elt->indx = from_ptr->indx;
      memcpy (to_elt->bits, from_ptr->bits, sizeof (to_elt->bits));

      /* Here we have a special case of bitmap_element_link, for the case
	 where we know the links are being entered in sequence.  */
      if (to_ptr == 0)
	{
	  to->first = to->current = to_elt;
	  to->indx = from_ptr->indx;
	  to_elt->next = to_elt->prev = 0;
	}
      else
	{
	  to_elt->prev = to_ptr;
	  to_elt->next = 0;
	  to_ptr->next = to_elt;
	}

      to_ptr = to_elt;
    }
}

/* Find a bitmap element that would hold a bitmap's bit.
   Update the `current' field even if we can't find an element that
   would hold the bitmap's bit to make eventual allocation
   faster.  */

static inline bitmap_element *
bitmap_find_bit (bitmap head, unsigned int bit)
{
  bitmap_element *element;
  unsigned int indx = bit / BITMAP_ELEMENT_ALL_BITS;

  if (head->current == 0
      || head->indx == indx)
    return head->current;

  if (head->indx < indx)
    /* INDX is beyond head->indx.  Search from head->current
       forward.  */
    for (element = head->current;
	 element->next != 0 && element->indx < indx;
	 element = element->next)
      ;

  else if (head->indx / 2 < indx)
    /* INDX is less than head->indx and closer to head->indx than to
       0.  Search from head->current backward.  */
    for (element = head->current;
	 element->prev != 0 && element->indx > indx;
	 element = element->prev)
      ;

  else
    /* INDX is less than head->indx and closer to 0 than to
       head->indx.  Search from head->first forward.  */
    for (element = head->first;
	 element->next != 0 && element->indx < indx;
	 element = element->next)
      ;

  /* `element' is the nearest to the one we want.  If it's not the one we
     want, the one we want doesn't exist.  */
  head->current = element;
  head->indx = element->indx;
  if (element != 0 && element->indx != indx)
    element = 0;

  return element;
}

/* Clear a single bit in a bitmap.  */

void
bitmap_clear_bit (bitmap head, int bit)
{
  bitmap_element *ptr = bitmap_find_bit (head, bit);

  if (ptr != 0)
    {
      unsigned bit_num  = bit % BITMAP_WORD_BITS;
      unsigned word_num = bit / BITMAP_WORD_BITS % BITMAP_ELEMENT_WORDS;
      ptr->bits[word_num] &= ~ (((BITMAP_WORD) 1) << bit_num);

      /* If we cleared the entire word, free up the element.  */
      if (bitmap_element_zerop (ptr))
	bitmap_element_free (head, ptr);
    }
}

/* Set a single bit in a bitmap.  */

void
bitmap_set_bit (bitmap head, int bit)
{
  bitmap_element *ptr = bitmap_find_bit (head, bit);
  unsigned word_num = bit / BITMAP_WORD_BITS % BITMAP_ELEMENT_WORDS;
  unsigned bit_num  = bit % BITMAP_WORD_BITS;
  BITMAP_WORD bit_val = ((BITMAP_WORD) 1) << bit_num;

  if (ptr == 0)
    {
      ptr = bitmap_element_allocate (head);
      ptr->indx = bit / BITMAP_ELEMENT_ALL_BITS;
      ptr->bits[word_num] = bit_val;
      bitmap_element_link (head, ptr);
    }
  else
    ptr->bits[word_num] |= bit_val;
}

/* Return whether a bit is set within a bitmap.  */

int
bitmap_bit_p (bitmap head, int bit)
{
  bitmap_element *ptr;
  unsigned bit_num;
  unsigned word_num;

  ptr = bitmap_find_bit (head, bit);
  if (ptr == 0)
    return 0;

  bit_num = bit % BITMAP_WORD_BITS;
  word_num = bit / BITMAP_WORD_BITS % BITMAP_ELEMENT_WORDS;

  return (ptr->bits[word_num] >> bit_num) & 1;
}

#if GCC_VERSION < 3400
/* Table of number of set bits in a character, indexed by value of char.  */
static unsigned char popcount_table[] = 
{
    0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4,1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,
    1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,
    1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,
    2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,
    1,2,2,3,2,3,3,4,2,3,3,4,3,4,4,5,2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,
    2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,
    2,3,3,4,3,4,4,5,3,4,4,5,4,5,5,6,3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,
    3,4,4,5,4,5,5,6,4,5,5,6,5,6,6,7,4,5,5,6,5,6,6,7,5,6,6,7,6,7,7,8,
};

static unsigned long
bitmap_popcount (BITMAP_WORD a)
{
  unsigned long ret = 0;
  unsigned i;

  /* Just do this the table way for now  */
  for (i = 0; i < BITMAP_WORD_BITS; i+= 8)
    ret += popcount_table[(a >> i) & 0xff];
  return ret;
}
#endif
/* Count the number of bits set in the bitmap, and return it.  */

unsigned long
bitmap_count_bits (bitmap a)
{
  unsigned long count = 0;
  bitmap_element *elt;
  unsigned ix;

  for (elt = a->first; elt; elt = elt->next)
    {
      for (ix = 0; ix != BITMAP_ELEMENT_WORDS; ix++)
	{
#if GCC_VERSION >= 3400
 	  /* Note that popcountl matches BITMAP_WORD in type, so the actual size
	 of BITMAP_WORD is not material.  */
	  count += __builtin_popcountl (elt->bits[ix]);
#else
	  count += bitmap_popcount (elt->bits[ix]);	  
#endif
	}
    }
  return count;
}
      


/* Return the bit number of the first set bit in the bitmap.  The
   bitmap must be non-empty.  */

unsigned
bitmap_first_set_bit (bitmap a)
{
  bitmap_element *elt = a->first;
  unsigned bit_no;
  BITMAP_WORD word;
  unsigned ix;
  
  gcc_assert (elt);
  bit_no = elt->indx * BITMAP_ELEMENT_ALL_BITS;
  for (ix = 0; ix != BITMAP_ELEMENT_WORDS; ix++)
    {
      word = elt->bits[ix];
      if (word)
	goto found_bit;
    }
  gcc_unreachable ();
 found_bit:
  bit_no += ix * BITMAP_WORD_BITS;

#if GCC_VERSION >= 3004
  gcc_assert (sizeof(long) == sizeof (word));
  bit_no += __builtin_ctzl (word);
#else
  /* Binary search for the first set bit.  */
#if BITMAP_WORD_BITS > 64
#error "Fill out the table."
#endif
#if BITMAP_WORD_BITS > 32
  if (!(word & 0xffffffff))
    word >>= 32, bit_no += 32;
#endif
  if (!(word & 0xffff))
    word >>= 16, bit_no += 16;
  if (!(word & 0xff))
    word >>= 8, bit_no += 8;
  if (!(word & 0xf))
    word >>= 4, bit_no += 4;
  if (!(word & 0x3))
    word >>= 2, bit_no += 2;
  if (!(word & 0x1))
    word >>= 1, bit_no += 1;
  
 gcc_assert (word & 1);
#endif
 return bit_no;
}


/* DST = A & B.  */

void
bitmap_and (bitmap dst, bitmap a, bitmap b)
{
  bitmap_element *dst_elt = dst->first;
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *dst_prev = NULL;

  gcc_assert (dst != a && dst != b);

  if (a == b)
    {
      bitmap_copy (dst, a);
      return;
    }

  while (a_elt && b_elt)
    {
      if (a_elt->indx < b_elt->indx)
	a_elt = a_elt->next;
      else if (b_elt->indx < a_elt->indx)
	b_elt = b_elt->next;
      else
	{
	  /* Matching elts, generate A & B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;

	  if (!dst_elt)
	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
	  else 
	    dst_elt->indx = a_elt->indx;
	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD r = a_elt->bits[ix] & b_elt->bits[ix];

	      dst_elt->bits[ix] = r;
	      ior |= r;
	    }
	  if (ior)
	    {
	      dst_prev = dst_elt;
	      dst_elt = dst_elt->next;
	    }
	  a_elt = a_elt->next;
	  b_elt = b_elt->next;
	}
    }
  bitmap_elt_clear_from (dst, dst_elt);
  gcc_assert (!dst->current == !dst->first);
  if (dst->current)
    dst->indx = dst->current->indx;
}

/* A &= B.  */

void
bitmap_and_into (bitmap a, bitmap b)
{
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *next;

  if (a == b) 
    return;

  while (a_elt && b_elt)
    {
      if (a_elt->indx < b_elt->indx)
	{
	  next = a_elt->next;
	  bitmap_element_free (a, a_elt);
	  a_elt = next;
	}
      else if (b_elt->indx < a_elt->indx)
	b_elt = b_elt->next;
      else
	{
	  /* Matching elts, generate A &= B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;

	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD r = a_elt->bits[ix] & b_elt->bits[ix];

	      a_elt->bits[ix] = r;
	      ior |= r;
	    }
	  next = a_elt->next;
	  if (!ior)
	    bitmap_element_free (a, a_elt);
	  a_elt = next;
	  b_elt = b_elt->next;
	}
    }
  bitmap_elt_clear_from (a, a_elt);
  gcc_assert (!a->current == !a->first);
  gcc_assert (!a->current || a->indx == a->current->indx);
}

/* DST = A & ~B  */

void
bitmap_and_compl (bitmap dst, bitmap a, bitmap b)
{
  bitmap_element *dst_elt = dst->first;
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *dst_prev = NULL;

  gcc_assert (dst != a && dst != b);
  
  if (a == b)
    {
      bitmap_clear (dst);
      return;
    }

  while (a_elt)
    {
      if (!b_elt || a_elt->indx < b_elt->indx)
	{
	  /* Copy a_elt.  */
	  if (!dst_elt)
	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
	  else
	    dst_elt->indx = a_elt->indx;
	  memcpy (dst_elt->bits, a_elt->bits, sizeof (dst_elt->bits));
	  dst_prev = dst_elt;
	  dst_elt = dst_elt->next;
	  a_elt = a_elt->next;
	}
      else if (b_elt->indx < a_elt->indx)
	b_elt = b_elt->next;
      else
	{
	  /* Matching elts, generate A & ~B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;

	  if (!dst_elt)
	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
	  else 
	    dst_elt->indx = a_elt->indx;
	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD r = a_elt->bits[ix] & ~b_elt->bits[ix];

	      dst_elt->bits[ix] = r;
	      ior |= r;
	    }
	  if (ior)
	    {
	      dst_prev = dst_elt;
	      dst_elt = dst_elt->next;
	    }
	  a_elt = a_elt->next;
	  b_elt = b_elt->next;
	}
    }
  bitmap_elt_clear_from (dst, dst_elt);
  gcc_assert (!dst->current == !dst->first);
  if (dst->current)
    dst->indx = dst->current->indx;
}

/* A &= ~B. Returns true if A changes */

bool
bitmap_and_compl_into (bitmap a, bitmap b)
{
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *next;
  BITMAP_WORD changed = 0;

  if (a == b)
    {
      if (bitmap_empty_p (a))
	return false;
      else
	{
	  bitmap_clear (a);
	  return true;
	}
    }

  while (a_elt && b_elt)
    {
      if (a_elt->indx < b_elt->indx)
	a_elt = a_elt->next;
      else if (b_elt->indx < a_elt->indx)
	b_elt = b_elt->next;
      else
	{
	  /* Matching elts, generate A &= ~B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;

	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD cleared = a_elt->bits[ix] & b_elt->bits[ix];
	      BITMAP_WORD r = a_elt->bits[ix] ^ cleared;

	      a_elt->bits[ix] = r;
	      changed |= cleared;
	      ior |= r;
	    }
	  next = a_elt->next;
	  if (!ior)
	    bitmap_element_free (a, a_elt);
	  a_elt = next;
	  b_elt = b_elt->next;
	}
    }
  gcc_assert (!a->current == !a->first);
  gcc_assert (!a->current || a->indx == a->current->indx);
  return changed != 0;
}

/* Clear COUNT bits from START in HEAD.  */
void
bitmap_clear_range (bitmap head, unsigned int start, unsigned int count)
{
  unsigned int first_index = start / BITMAP_ELEMENT_ALL_BITS;
  unsigned int end_bit_plus1 = start + count;
  unsigned int end_bit = end_bit_plus1 - 1;
  unsigned int last_index = (end_bit) / BITMAP_ELEMENT_ALL_BITS;
  bitmap_element *elt = bitmap_find_bit (head, start);

  /* If bitmap_find_bit returns zero, the current is the closest block
     to the result.  If the current is less than first index, find the
     next one.  Otherwise, just set elt to be current.  */
  if (!elt)
    { 
      if (head->current)
	{
	  if (head->indx < first_index)
	    {
	      elt = head->current->next;
	      if (!elt)
		return;
	    }
	  else 
	    elt = head->current;
	}
      else
	return;
    }

  while (elt && (elt->indx <= last_index))
    {
      bitmap_element * next_elt = elt->next;
      unsigned elt_start_bit = (elt->indx) * BITMAP_ELEMENT_ALL_BITS;
      unsigned elt_end_bit_plus1 = elt_start_bit + BITMAP_ELEMENT_ALL_BITS;


      if (elt_start_bit >= start && elt_end_bit_plus1 <= end_bit_plus1)
	/* Get rid of the entire elt and go to the next one.  */
	bitmap_element_free (head, elt);
      else 
	{
	  /* Going to have to knock out some bits in this elt.  */
	  unsigned int first_word_to_mod; 
	  BITMAP_WORD first_mask; 
	  unsigned int last_word_to_mod;
	  BITMAP_WORD last_mask;
	  unsigned int i;
	  bool clear = true;

	  if (elt_start_bit <= start)
	    {
	      /* The first bit to turn off is somewhere inside this
		 elt.  */
	      first_word_to_mod = (start - elt_start_bit) / BITMAP_WORD_BITS;

	      /* This mask should have 1s in all bits >= start position. */
	      first_mask = 
		(((BITMAP_WORD) 1) << ((start % BITMAP_WORD_BITS))) - 1;
	      first_mask = ~first_mask;
	    }
	  else
	    {
	      /* The first bit to turn off is below this start of this elt.  */
	      first_word_to_mod = 0;
	      first_mask = 0;
	      first_mask = ~first_mask;
	    }	      
	    
	  if (elt_end_bit_plus1 <= end_bit_plus1)
	    {
	      /* The last bit to turn off is beyond this elt.  */
	      last_word_to_mod = BITMAP_ELEMENT_WORDS - 1;
	      last_mask = 0;
	      last_mask = ~last_mask;
	    }
	  else
	    {
	      /* The last bit to turn off is inside to this elt.  */
	      last_word_to_mod = 
		(end_bit_plus1 - elt_start_bit) / BITMAP_WORD_BITS;

	      /* The last mask should have 1s below the end bit.  */
	      last_mask = 
		(((BITMAP_WORD) 1) << (((end_bit_plus1) % BITMAP_WORD_BITS))) - 1;
	    }


	  if (first_word_to_mod == last_word_to_mod)
	    {
	      BITMAP_WORD mask = first_mask & last_mask;
	      elt->bits[first_word_to_mod] &= ~mask;
	    }
	  else
	    {
	      elt->bits[first_word_to_mod] &= ~first_mask;
	      for (i = first_word_to_mod + 1; i < last_word_to_mod; i++)
		elt->bits[i] = 0;
	      elt->bits[last_word_to_mod] &= ~last_mask;
	    }
	  for (i = 0; i < BITMAP_ELEMENT_WORDS; i++)
	    if (elt->bits[i])
	      {
		clear = false;
		break;
	      }
	  /* Check to see if there are any bits left.  */
	  if (clear)
	    bitmap_element_free (head, elt);
	}
      elt = next_elt;
    }
  
  if (elt)
    {
      head->current = elt;
      head->indx = head->current->indx;
    }
}

/* A = ~A & B. */

void
bitmap_compl_and_into (bitmap a, bitmap b)
{
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *a_prev = NULL;
  bitmap_element *next;

  gcc_assert (a != b);

  if (bitmap_empty_p (a))
    {
      bitmap_copy (a, b);
      return;
    }
  if (bitmap_empty_p (b))
    {
      bitmap_clear (a);
      return;
    }

  while (a_elt || b_elt)
    {
      if (!b_elt || (a_elt && a_elt->indx < b_elt->indx))
	{
	  /* A is before B.  Remove A */
	  next = a_elt->next;
	  a_prev = a_elt->prev;
	  bitmap_element_free (a, a_elt);
	  a_elt = next;
	}
      else if (!a_elt || b_elt->indx < a_elt->indx)
	{
	  /* B is before A.  Copy B. */
	  next = bitmap_elt_insert_after (a, a_prev, b_elt->indx);
	  memcpy (next->bits, b_elt->bits, sizeof (next->bits));
	  a_prev = next;
	  b_elt = b_elt->next;
	}
      else
	{
	  /* Matching elts, generate A = ~A & B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;

	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD cleared = a_elt->bits[ix] & b_elt->bits[ix];
	      BITMAP_WORD r = b_elt->bits[ix] ^ cleared;

	      a_elt->bits[ix] = r;
	      ior |= r;
	    }
	  next = a_elt->next;
	  if (!ior)
	    bitmap_element_free (a, a_elt);
	  else
	    a_prev = a_elt;
	  a_elt = next;
	  b_elt = b_elt->next;
	}
    }
  gcc_assert (!a->current == !a->first);
  gcc_assert (!a->current || a->indx == a->current->indx);
  return;
}

/* DST = A | B.  Return true if DST changes.  */

bool
bitmap_ior (bitmap dst, bitmap a, bitmap b)
{
  bitmap_element *dst_elt = dst->first;
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *dst_prev = NULL;
  bool changed = false;  

  gcc_assert (dst != a && dst != b);

  while (a_elt || b_elt)
    {
      if (a_elt && b_elt && a_elt->indx == b_elt->indx)
	{
	  /* Matching elts, generate A | B.  */
	  unsigned ix;
	      
	  if (!changed && dst_elt && dst_elt->indx == a_elt->indx)
	    {
	      for (ix = BITMAP_ELEMENT_WORDS; ix--;)
		{
		  BITMAP_WORD r = a_elt->bits[ix] | b_elt->bits[ix];

		  if (r != dst_elt->bits[ix])
		    {
		      dst_elt->bits[ix] = r;
		      changed = true;
		    }
		}
	    }
	  else
	    {
	      changed = true;
	      if (!dst_elt)
		dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
	      else 
		dst_elt->indx = a_elt->indx;
	      for (ix = BITMAP_ELEMENT_WORDS; ix--;)
		{
		  BITMAP_WORD r = a_elt->bits[ix] | b_elt->bits[ix];
		  
		  dst_elt->bits[ix] = r;
		}
	    }
	  a_elt = a_elt->next;
	  b_elt = b_elt->next;
	  dst_prev = dst_elt;
	  dst_elt = dst_elt->next;
	}
      else
	{
	  /* Copy a single element.  */
	  bitmap_element *src;

	  if (!b_elt || (a_elt && a_elt->indx < b_elt->indx))
	    {
	      src = a_elt;
	      a_elt = a_elt->next;
	    }
	  else
	    {
	      src = b_elt;
	      b_elt = b_elt->next;
	    }

	  if (!changed && dst_elt && dst_elt->indx == src->indx)
	    {
	      unsigned ix;
	      
	      for (ix = BITMAP_ELEMENT_WORDS; ix--;)
		if (src->bits[ix] != dst_elt->bits[ix])
		  {
		    dst_elt->bits[ix] = src->bits[ix];
		    changed = true;
		  }
	    }
	  else
	    {
	      changed = true;
	      if (!dst_elt)
		dst_elt = bitmap_elt_insert_after (dst, dst_prev, src->indx);
	      else 
		dst_elt->indx = src->indx;
	      memcpy (dst_elt->bits, src->bits, sizeof (dst_elt->bits));
	    }
	  
	  dst_prev = dst_elt;
	  dst_elt = dst_elt->next;
	}
    }

  if (dst_elt)
    {
      changed = true;
      bitmap_elt_clear_from (dst, dst_elt);
    }
  gcc_assert (!dst->current == !dst->first);
  if (dst->current)
    dst->indx = dst->current->indx;
  return changed;
}

/* A |= B.  Return true if A changes.  */

bool
bitmap_ior_into (bitmap a, bitmap b)
{
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *a_prev = NULL;
  bool changed = false;

  if (a == b)
    return false;

  while (b_elt)
    {
      if (!a_elt || b_elt->indx < a_elt->indx)
	{
	  /* Copy b_elt.  */
	  bitmap_element *dst = bitmap_elt_insert_after (a, a_prev, b_elt->indx);
	  memcpy (dst->bits, b_elt->bits, sizeof (dst->bits));
	  a_prev = dst;
	  b_elt = b_elt->next;
	  changed = true;
	}
      else if (a_elt->indx < b_elt->indx)
	{
	  a_prev = a_elt;
	  a_elt = a_elt->next;
	}
      else
	{
	  /* Matching elts, generate A |= B.  */
	  unsigned ix;

	  if (changed)
	    for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	      {
		BITMAP_WORD r = a_elt->bits[ix] | b_elt->bits[ix];
		
		a_elt->bits[ix] = r;
	      }
	  else
	    for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	      {
		BITMAP_WORD r = a_elt->bits[ix] | b_elt->bits[ix];

		if (a_elt->bits[ix] != r)
		  {
		    changed = true;
		    a_elt->bits[ix] = r;
		  }
	      }
	  b_elt = b_elt->next;
	  a_prev = a_elt;
	  a_elt = a_elt->next;
	}
    }
  gcc_assert (!a->current == !a->first);
  if (a->current)
    a->indx = a->current->indx;
  return changed;
}

/* DST = A ^ B  */

void
bitmap_xor (bitmap dst, bitmap a, bitmap b)
{
  bitmap_element *dst_elt = dst->first;
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *dst_prev = NULL;

  gcc_assert (dst != a && dst != b);
  if (a == b)
    {
      bitmap_clear (dst);
      return;
    }

  while (a_elt || b_elt)
    {
      if (a_elt && b_elt && a_elt->indx == b_elt->indx)
	{
	  /* Matching elts, generate A ^ B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;

	  if (!dst_elt)
	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, a_elt->indx);
	  else
	    dst_elt->indx = a_elt->indx;
	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD r = a_elt->bits[ix] ^ b_elt->bits[ix];

	      ior |= r;
	      dst_elt->bits[ix] = r;
	    }
	  a_elt = a_elt->next;
	  b_elt = b_elt->next;
	  if (ior)
	    {
	      dst_prev = dst_elt;
	      dst_elt = dst_elt->next;
	    }
	}
      else
	{
	  /* Copy a single element.  */
	  bitmap_element *src;

	  if (!b_elt || (a_elt && a_elt->indx < b_elt->indx))
	    {
	      src = a_elt;
	      a_elt = a_elt->next;
	    }
	  else
	    {
	      src = b_elt;
	      b_elt = b_elt->next;
	    }

	  if (!dst_elt)
	    dst_elt = bitmap_elt_insert_after (dst, dst_prev, src->indx);
	  else 
	    dst_elt->indx = src->indx;
	  memcpy (dst_elt->bits, src->bits, sizeof (dst_elt->bits));
	  dst_prev = dst_elt;
	  dst_elt = dst_elt->next;
	}
    }
  bitmap_elt_clear_from (dst, dst_elt);
  gcc_assert (!dst->current == !dst->first);
  if (dst->current)
    dst->indx = dst->current->indx;
}

/* A ^= B */

void
bitmap_xor_into (bitmap a, bitmap b)
{
  bitmap_element *a_elt = a->first;
  bitmap_element *b_elt = b->first;
  bitmap_element *a_prev = NULL;

  if (a == b)
    {
      bitmap_clear (a);
      return;
    }

  while (b_elt)
    {
      if (!a_elt || b_elt->indx < a_elt->indx)
	{
	  /* Copy b_elt.  */
	  bitmap_element *dst = bitmap_elt_insert_after (a, a_prev, b_elt->indx);
	  memcpy (dst->bits, b_elt->bits, sizeof (dst->bits));
	  a_prev = dst;
	  b_elt = b_elt->next;
	}
      else if (a_elt->indx < b_elt->indx)
	{
	  a_prev = a_elt;
	  a_elt = a_elt->next;
	}
      else
	{
	  /* Matching elts, generate A ^= B.  */
	  unsigned ix;
	  BITMAP_WORD ior = 0;
	  bitmap_element *next = a_elt->next;

	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    {
	      BITMAP_WORD r = a_elt->bits[ix] ^ b_elt->bits[ix];

	      ior |= r;
	      a_elt->bits[ix] = r;
	    }
	  b_elt = b_elt->next;
	  if (ior)
	    a_prev = a_elt;
	  else
	    bitmap_element_free (a, a_elt);
	  a_elt = next;
	}
    }
  gcc_assert (!a->current == !a->first);
  if (a->current)
    a->indx = a->current->indx;
}

/* Return true if two bitmaps are identical.
   We do not bother with a check for pointer equality, as that never
   occurs in practice.  */

bool
bitmap_equal_p (bitmap a, bitmap b)
{
  bitmap_element *a_elt;
  bitmap_element *b_elt;
  unsigned ix;
  
  for (a_elt = a->first, b_elt = b->first;
       a_elt && b_elt;
       a_elt = a_elt->next, b_elt = b_elt->next)
    {
      if (a_elt->indx != b_elt->indx)
	return false;
      for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	if (a_elt->bits[ix] != b_elt->bits[ix])
	  return false;
    }
  return !a_elt && !b_elt;
}

/* Return true if A AND B is not empty.  */

bool
bitmap_intersect_p (bitmap a, bitmap b)
{
  bitmap_element *a_elt;
  bitmap_element *b_elt;
  unsigned ix;
  
  for (a_elt = a->first, b_elt = b->first;
       a_elt && b_elt;)
    {
      if (a_elt->indx < b_elt->indx)
	a_elt = a_elt->next;
      else if (b_elt->indx < a_elt->indx)
	b_elt = b_elt->next;
      else
	{
	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    if (a_elt->bits[ix] & b_elt->bits[ix])
	      return true;
	  a_elt = a_elt->next;
	  b_elt = b_elt->next;
	}
    }
  return false;
}

/* Return true if A AND NOT B is not empty.  */

bool
bitmap_intersect_compl_p (bitmap a, bitmap b)
{
  bitmap_element *a_elt;
  bitmap_element *b_elt;
  unsigned ix;
  for (a_elt = a->first, b_elt = b->first;
       a_elt && b_elt;)
    {
      if (a_elt->indx < b_elt->indx)
	return true;
      else if (b_elt->indx < a_elt->indx)
	b_elt = b_elt->next;
      else
	{
	  for (ix = BITMAP_ELEMENT_WORDS; ix--;)
	    if (a_elt->bits[ix] & ~b_elt->bits[ix])
	      return true;
	  a_elt = a_elt->next;
	  b_elt = b_elt->next;
	}
    }
  return a_elt != NULL;
}


/* DST = A | (FROM1 & ~FROM2).  Return true if DST changes.  */

bool
bitmap_ior_and_compl (bitmap dst, bitmap a, bitmap from1, bitmap from2)
{
  bitmap_head tmp;
  bool changed;

  bitmap_initialize (&tmp, &bitmap_default_obstack);
  bitmap_and_compl (&tmp, from1, from2);
  changed = bitmap_ior (dst, a, &tmp);
  bitmap_clear (&tmp);

  return changed;
}

/* A |= (FROM1 & ~FROM2).  Return true if A changes.  */

bool
bitmap_ior_and_compl_into (bitmap a, bitmap from1, bitmap from2)
{
  bitmap_head tmp;
  bool changed;
  
  bitmap_initialize (&tmp, &bitmap_default_obstack);
  bitmap_and_compl (&tmp, from1, from2);
  changed = bitmap_ior_into (a, &tmp);
  bitmap_clear (&tmp);

  return changed;
}

/* Debugging function to print out the contents of a bitmap.  */

void
debug_bitmap_file (FILE *file, bitmap head)
{
  bitmap_element *ptr;

  fprintf (file, "\nfirst = %p current = %p indx = %u\n",
	   (void *) head->first, (void *) head->current, head->indx);

  for (ptr = head->first; ptr; ptr = ptr->next)
    {
      unsigned int i, j, col = 26;

      fprintf (file, "\t%p next = %p prev = %p indx = %u\n\t\tbits = {",
	       (void*) ptr, (void*) ptr->next, (void*) ptr->prev, ptr->indx);

      for (i = 0; i < BITMAP_ELEMENT_WORDS; i++)
	for (j = 0; j < BITMAP_WORD_BITS; j++)
	  if ((ptr->bits[i] >> j) & 1)
	    {
	      if (col > 70)
		{
		  fprintf (file, "\n\t\t\t");
		  col = 24;
		}

	      fprintf (file, " %u", (ptr->indx * BITMAP_ELEMENT_ALL_BITS
				     + i * BITMAP_WORD_BITS + j));
	      col += 4;
	    }

      fprintf (file, " }\n");
    }
}

/* Function to be called from the debugger to print the contents
   of a bitmap.  */

void
debug_bitmap (bitmap head)
{
  debug_bitmap_file (stdout, head);
}

/* Function to print out the contents of a bitmap.  Unlike debug_bitmap_file,
   it does not print anything but the bits.  */

void
bitmap_print (FILE *file, bitmap head, const char *prefix, const char *suffix)
{
  const char *comma = "";
  unsigned i;
  bitmap_iterator bi;

  fputs (prefix, file);
  EXECUTE_IF_SET_IN_BITMAP (head, 0, i, bi)
    {
      fprintf (file, "%s%d", comma, i);
      comma = ", ";
    }
  fputs (suffix, file);
}

#include "gt-bitmap.h"