gecko-dev/xpcom/ds/nsCheapSets.h

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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 * for the specific language governing rights and limitations under the
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 * The Original Code is Mozilla Communicator client code.
 *
 * The Initial Developer of the Original Code is
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#ifndef __nsCheapSets_h__
#define __nsCheapSets_h__

#include "nsHashSets.h"

/**
 * A string set that takes up minimal size when there are 0 or 1 strings in the
 * set.  Use for cases where sizes of 0 and 1 are even slightly common.
 */
class nsCheapStringSet {
public:
  nsCheapStringSet() : mValOrHash(nsnull)
  {
  }
  ~nsCheapStringSet();

  /**
   * Put a string into the set
   * @param aVal the value to put in
   */
  nsresult Put(const nsAString& aVal);

  /**
   * Remove a string from the set
   * @param aVal the string to remove
   */
  void Remove(const nsAString& aVal);

  /**
   * Check if the set contains a particular string
   * @param aVal the string to check for
   * @return whether the string is in the set
   */
  PRBool Contains(const nsAString& aVal)
  {
    nsStringHashSet* set = GetHash();
    // Check the value from the hash if the hash is there
    if (set) {
      return set->Contains(aVal);
    }

    // Check whether the value is equal to the string if the string is there
    nsAString* str = GetStr();
    return str && str->Equals(aVal);
  }

private:
  typedef PRUword PtrBits;

  /** Get the hash pointer (or null if we're not a hash) */
  nsStringHashSet* GetHash()
  {
    return (PtrBits(mValOrHash) & 0x1) ? nsnull : (nsStringHashSet*)mValOrHash;
  }
  /** Find out whether it is a string */
  nsAString* GetStr()
  {
    return (PtrBits(mValOrHash) & 0x1)
           ? (nsAString*)(PtrBits(mValOrHash) & ~0x1)
           : nsnull;
  }
  /** Set the single string */
  nsresult SetStr(const nsAString& aVal)
  {
    nsString* str = new nsString(aVal);
    if (!str) {
      return NS_ERROR_OUT_OF_MEMORY;
    }
    mValOrHash = (nsAString*)(PtrBits(str) | 0x1);
    return NS_OK;
  }
  /** Initialize the hash */
  nsresult InitHash(nsStringHashSet** aSet);

private:
  /** A hash or string ptr, depending on the lower bit (0=hash, 1=string) */
  void* mValOrHash;
};


/**
 * An integer set that takes up only 4 bytes when there are 0 or 1 integers
 * in the set.  Use for cases where sizes of 0 and 1 are even slightly common.
 */
class nsCheapInt32Set {
public:
  nsCheapInt32Set() : mValOrHash(nsnull)
  {
  }
  ~nsCheapInt32Set();

  /**
   * Put an int into the set
   */
  nsresult Put(PRInt32 aVal);
 
  /**
   * Remove a int from the set
   * @param aVal the int to remove
   */
  void Remove(PRInt32 aVal);

  /**
   * Check if the set contains a particular int
   * @param aVal the int to check for
   * @return whether the int is in the set
   */
  PRBool Contains(PRInt32 aVal)
  {
    nsInt32HashSet* set = GetHash();
    if (set) {
      return set->Contains(aVal);
    }
    if (IsInt()) {
      return GetInt() == aVal;
    }
    return PR_FALSE;
  }

private:
  typedef PRUword PtrBits;

  /** Get the hash pointer (or null if we're not a hash) */
  nsInt32HashSet* GetHash()
  {
    return PtrBits(mValOrHash) & 0x1 ? nsnull : (nsInt32HashSet*)mValOrHash;
  }
  /** Find out whether it is an integer */
  PRBool IsInt()
  {
    return !!(PtrBits(mValOrHash) & 0x1);
  }
  /** Get the single integer */
  PRInt32 GetInt()
  {
    return PtrBits(mValOrHash) >> 1;
  }
  /** Set the single integer */
  void SetInt(PRInt32 aInt)
  {
    mValOrHash = (void*)((aInt << 1) | 0x1);
  }
  /** Create the hash and initialize */
  nsresult InitHash(nsInt32HashSet** aSet);

private:
  /** A hash or int, depending on the lower bit (0=hash, 1=int) */
  void* mValOrHash;
};


/**
 * XXX We may want an nsCheapVoidSet and nsCheapCStringSet at some point
 */


#endif