Ok, no code is left in src, it's all in src/old. We'll gradually move code back

into src as it's fixed and re-org'd.  This includes tests, which, I may write a
unit test system into libbu++ just to make my life easier.

1 files changed, 207 insertions, 0 deletions

diff --git a/src/old/tqsort.h b/src/old/tqsort.h
new file mode 100644
index 0000000..c836b4f
--- /dev/null
+++ b/src/old/tqsort.h
@@ -0,0 +1,207 @@
+#ifndef T_QSORT_H
+#define T_QSORT_H
+
+#define _QSORT_SWAP(a, b, t) ((void)((t = *a), (*a = *b), (*b = t)))
+
+/* Discontinue quicksort algorithm when partition gets below this size.
+   This particular magic number was chosen to work best on a Sun 4/260. */
+#define _QSORT_MAX_THRESH 4
+
+/* Stack node declarations used to store unfulfilled partition obligations
+ * (inlined in QSORT).
+typedef struct {
+  QSORT_TYPE *_lo, *_hi;
+} qsort_stack_node;
+ */
+
+/* The next 4 #defines implement a very fast in-line stack abstraction. */
+/* The stack needs log (total_elements) entries (we could even subtract
+   log(MAX_THRESH)).  Since total_elements has type unsigned, we get as
+   upper bound for log (total_elements):
+   bits per byte (CHAR_BIT) * sizeof(unsigned).  */
+#define _QSORT_STACK_SIZE       (8 * sizeof(unsigned))
+#define _QSORT_PUSH(top, low, high)     \
+        (((top->_lo = (low)), (top->_hi = (high)), ++top))
+#define _QSORT_POP(low, high, top)      \
+        ((--top, (low = top->_lo), (high = top->_hi)))
+#define _QSORT_STACK_NOT_EMPTY  (_stack < _top)
+
+
+/* Order size using quicksort.  This implementation incorporates
+   four optimizations discussed in Sedgewick:
+
+   1. Non-recursive, using an explicit stack of pointer that store the
+      next array partition to sort.  To save time, this maximum amount
+      of space required to store an array of SIZE_MAX is allocated on the
+      stack.  Assuming a 32-bit (64 bit) integer for size_t, this needs
+      only 32 * sizeof(stack_node) == 256 bytes (for 64 bit: 1024 bytes).
+      Pretty cheap, actually.
+
+   2. Chose the pivot element using a median-of-three decision tree.
+      This reduces the probability of selecting a bad pivot value and
+      eliminates certain extraneous comparisons.
+
+   3. Only quicksorts TOTAL_ELEMS / MAX_THRESH partitions, leaving
+      insertion sort to order the MAX_THRESH items within each partition.
+      This is a big win, since insertion sort is faster for small, mostly
+      sorted array segments.
+
+   4. The larger of the two sub-partitions is always pushed onto the
+      stack first, with the algorithm then concentrating on the
+      smaller partition.  This *guarantees* no more than log (total_elems)
+      stack size is needed (actually O(1) in this case)!  */
+
+/* The main code starts here... */
+
+template<typename QSORT_TYPE, typename QSORT_LTT, typename CST>
+void tqsort( QSORT_TYPE *QSORT_BASE, int QSORT_NELT )
+{
+  QSORT_LTT QSORT_LT;
+  QSORT_TYPE *const _base = (QSORT_BASE);
+  const unsigned _elems = (QSORT_NELT);
+  QSORT_TYPE _hold;
+
+  /* Don't declare two variables of type QSORT_TYPE in a single
+   * statement: eg `TYPE a, b;', in case if TYPE is a pointer,
+   * expands to `type* a, b;' wich isn't what we want.
+   */
+
+  if (_elems > _QSORT_MAX_THRESH) {
+    QSORT_TYPE *_lo = _base;
+    QSORT_TYPE *_hi = _lo + _elems - 1;
+    struct {
+      QSORT_TYPE *_hi; QSORT_TYPE *_lo;
+    } _stack[_QSORT_STACK_SIZE], *_top = _stack + 1;
+
+    while (_QSORT_STACK_NOT_EMPTY) {
+      QSORT_TYPE *_left_ptr; QSORT_TYPE *_right_ptr;
+
+      /* Select median value from among LO, MID, and HI. Rearrange
+         LO and HI so the three values are sorted. This lowers the
+         probability of picking a pathological pivot value and  
+         skips a comparison for both the LEFT_PTR and RIGHT_PTR in
+         the while loops. */
+                                                                        
+      QSORT_TYPE *_mid = _lo + ((_hi - _lo) >> 1);                      
+                                                                        
+      if (QSORT_LT ((CST)(_mid), (CST)(_lo)))                                           
+        _QSORT_SWAP (_mid, _lo, _hold);                                 
+      if (QSORT_LT ((CST)(_hi), (CST)(_mid)))                                           
+        _QSORT_SWAP (_mid, _hi, _hold);                                 
+      else                                                              
+        goto _jump_over;                                                
+      if (QSORT_LT ((CST)(_mid), (CST)(_lo)))                                   
+        _QSORT_SWAP (_mid, _lo, _hold);                                 
+  _jump_over:;                                                          
+                                                                        
+      _left_ptr  = _lo + 1;                                             
+      _right_ptr = _hi - 1;                                     
+                                                                        
+      /* Here's the famous ``collapse the walls'' section of quicksort. 
+         Gotta like those tight inner loops!  They are the main reason  
+         that this algorithm runs much faster than others. */           
+      do {                                                              
+        while (QSORT_LT ((CST)(_left_ptr), (CST)(_mid)))                                
+         ++_left_ptr;                                                   
+                                                                        
+        while (QSORT_LT ((CST)(_mid), (CST)(_right_ptr)))                               
+          --_right_ptr;                                                 
+                                                                        
+        if (_left_ptr < _right_ptr) {                                   
+          _QSORT_SWAP (_left_ptr, _right_ptr, _hold);                   
+          if (_mid == _left_ptr)                                        
+            _mid = _right_ptr;                                          
+          else if (_mid == _right_ptr)                                  
+            _mid = _left_ptr;                                           
+          ++_left_ptr;                                          
+          --_right_ptr;                                                 
+        }                                                               
+        else if (_left_ptr == _right_ptr) {                             
+          ++_left_ptr;                                                  
+                  --_right_ptr;                                                 
+          break;                                                        
+        }                                                               
+      } while (_left_ptr <= _right_ptr);                                
+                                                                        
+     /* Set up pointers for next iteration.  First determine whether    
+        left and right partitions are below the threshold size.  If so, 
+        ignore one or both.  Otherwise, push the larger partition's     
+        bounds on the stack and continue sorting the smaller one. */    
+                                                                        
+      if (_right_ptr - _lo <= _QSORT_MAX_THRESH) {                      
+        if (_hi - _left_ptr <= _QSORT_MAX_THRESH)               
+          /* Ignore both small partitions. */                           
+          _QSORT_POP (_lo, _hi, _top);                                  
+        else                                                            
+          /* Ignore small left partition. */                            
+          _lo = _left_ptr;                                              
+      }                                                                 
+      else if (_hi - _left_ptr <= _QSORT_MAX_THRESH)                    
+        /* Ignore small right partition. */                             
+        _hi = _right_ptr;                                               
+      else if (_right_ptr - _lo > _hi - _left_ptr) {                    
+        /* Push larger left partition indices. */                       
+        _QSORT_PUSH (_top, _lo, _right_ptr);                    
+        _lo = _left_ptr;                                                
+      }                                                                 
+      else {                                                            
+        /* Push larger right partition indices. */                      
+        _QSORT_PUSH (_top, _left_ptr, _hi);                             
+        _hi = _right_ptr;                                               
+      }                                                                 
+    }                                                           
+  }                                                                     
+                                                                        
+  /* Once the BASE array is partially sorted by quicksort the rest      
+     is completely sorted using insertion sort, since this is efficient 
+     for partitions below MAX_THRESH size. BASE points to the           
+     beginning of the array to sort, and END_PTR points at the very     
+     last element in the array (*not* one beyond it!). */               
+                                                                        
+  {                                                                     
+    QSORT_TYPE *const _end_ptr = _base + _elems - 1;                    
+    QSORT_TYPE *_tmp_ptr = _base;                                       
+    register QSORT_TYPE *_run_ptr;                              
+    QSORT_TYPE *_thresh;                                                
+                                                                        
+    _thresh = _base + _QSORT_MAX_THRESH;                                
+    if (_thresh > _end_ptr)                                             
+      _thresh = _end_ptr;                                       
+                                                                        
+    /* Find smallest element in first threshold and place it at the     
+       array's beginning.  This is the smallest array element,          
+       and the operation speeds up insertion sort's inner loop. */      
+                                                                        
+    for (_run_ptr = _tmp_ptr + 1; _run_ptr <= _thresh; ++_run_ptr)      
+      if (QSORT_LT ((CST)(_run_ptr), (CST)(_tmp_ptr)))                          
+        _tmp_ptr = _run_ptr;                                            
+                                                                        
+    if (_tmp_ptr != _base)                                              
+      _QSORT_SWAP (_tmp_ptr, _base, _hold);                             
+                                                                        
+    /* Insertion sort, running from left-hand-side                      
+     * up to right-hand-side.  */                                       
+                                                                        
+    _run_ptr = _base + 1;                                               
+    while (++_run_ptr <= _end_ptr) {                                    
+      _tmp_ptr = _run_ptr - 1;                                          
+      while (QSORT_LT ((CST)(_run_ptr), (CST)(_tmp_ptr)))                               
+        --_tmp_ptr;                                                     
+                                                                        
+      ++_tmp_ptr;                                                       
+      if (_tmp_ptr != _run_ptr) {                                       
+        QSORT_TYPE *_trav = _run_ptr + 1;                               
+        while (--_trav >= _run_ptr) {                                   
+          QSORT_TYPE *_hi; QSORT_TYPE *_lo;                             
+          _hold = *_trav;                                               
+                                                                        
+          for (_hi = _lo = _trav; --_lo >= _tmp_ptr; _hi = _lo)         
+            *_hi = *_lo;                                                
+          *_hi = _hold;                                                 
+        }                                                               
+      }                                                                 
+    }                                                                   
+  }                                                                     
+}
+
+#endif