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// $Id: Stack.pike,v 1.4 2002/03/18 01:29:48 mast Exp $ 
 
//! This class implements a simple stack. Instead of adding and removing 
//! elements to an array, and thus making it vary in size for every push 
//! and pop operation, this stack tries to keep the stack size constant. 
//! If however the stack risks to overflow, it will allocate double its 
//! current size, i.e. pushing an element on an full 32 slot stack will 
//! result in a 64 slot stack with 33 elements. 
 
int ptr; 
array arr; 
 
//! Push an element on the top of the stack. 
void push(mixed val) 
{ 
  if(ptr == sizeof(arr)) { 
    arr += allocate(ptr); 
  } 
  arr[ptr++] = val; 
} 
 
//! Returns the top element from the stack, without 
//! popping it. 
mixed top() 
{ 
  if (ptr) { 
    return(arr[ptr-1]); 
  } 
  error("Stack underflow\n"); 
} 
 
//! Pops @[val] entries from the stack, or one entry 
//! if no value is given. The popped entries are not 
//! actually freed, only the stack pointer is moved. 
void quick_pop(void|int val) 
{ 
  if (val) { 
    if (ptr < val) { 
        ptr = 0; 
    } else { 
        ptr -= val; 
    } 
  } else { 
    if (ptr > 0) { 
        ptr--; 
    } 
  } 
} 
 
//! Pops and returns entry @[val] from the stack, counting 
//! from the top. If no value is given the top element is 
//! popped and returned. All popped entries are freed from 
//! the stack. 
mixed pop(void|int val) 
{ 
  mixed foo; 
 
  if (val) { 
    if (ptr <= 0) { 
        error("Stack underflow\n"); 
    } 
 
    if (ptr < val) { 
      val = ptr; 
    } 
    ptr -= val; 
    foo = arr[ptr..ptr + val - 1]; 
 
    for (int i=0; i < val; i++) { 
      arr[ptr + i] = 0;       /* Don't waste references */ 
    } 
  } else { 
    if(--ptr < 0) 
        error("Stack underflow\n"); 
   
    foo=arr[ptr]; 
    arr[ptr]=0; /* Don't waste references */ 
  } 
  return foo; 
} 
 
//! Empties the stack, resets the stack pointer 
//! and shrinks the stack size to the given value 
//! or 32 if none is given. 
//! @seealso 
//!   @[create] 
void reset(int|void initial_size) 
{ 
  arr = allocate(initial_size || 32); 
  ptr = 0; 
} 
 
//! An initial stack size can be given when 
//! a stack is cloned. The default value is 
//! 32. 
void create(int|void initial_size) 
{ 
  arr = allocate(initial_size || 32); 
}