Initial checkin

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6414 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 251 insertions, 0 deletions

diff --git a/runtime/GCCLibraries/libc/qsort.c b/runtime/GCCLibraries/libc/qsort.c
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+/* Copyright (C) 1991, 1992, 1996, 1997, 1999 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Written by Douglas C. Schmidt (schmidt@ics.uci.edu).
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, write to the Free
+   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+   02111-1307 USA.  */
+
+/* If you consider tuning this algorithm, you should consult first:
+   Engineering a sort function; Jon Bentley and M. Douglas McIlroy;
+   Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993.  */
+
+#if 0
+
+#include <limits.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* Byte-wise swap two items of size SIZE. */
+#define SWAP(a, b, size)                                                      \
+  do                                                                          \
+    {                                                                         \
+      register size_t __size = (size);                                        \
+      register char *__a = (a), *__b = (b);                                   \
+      do                                                                      \
+        {                                                                      \
+          char __tmp = *__a;                                                      \
+          *__a++ = *__b;                                                      \
+          *__b++ = __tmp;                                                      \
+        } while (--__size > 0);                                                      \
+    } while (0)
+
+/* Discontinue quicksort algorithm when partition gets below this size.
+   This particular magic number was chosen to work best on a Sun 4/260. */
+#define MAX_THRESH 4
+
+/* Stack node declarations used to store unfulfilled partition obligations. */
+typedef struct
+  {
+    char *lo;
+    char *hi;
+  } 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 size_t, we get as
+   upper bound for log (total_elements):
+   bits per byte (CHAR_BIT) * sizeof(size_t).  */
+#define STACK_SIZE      (CHAR_BIT * sizeof(size_t))
+#define PUSH(low, high) ((void) ((top->lo = (low)), (top->hi = (high)), ++top))
+#define POP(low, high)        ((void) (--top, (low = top->lo), (high = top->hi)))
+#define 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)!  */
+
+typedef int(*__compar_fn_t)(const void *, const void *);
+void
+qsort (void *const pbase, size_t total_elems, size_t size,
+            __compar_fn_t cmp)
+{
+  register char *base_ptr = (char *) pbase;
+
+  const size_t max_thresh = MAX_THRESH * size;
+
+  if (total_elems == 0)
+    /* Avoid lossage with unsigned arithmetic below.  */
+    return;
+
+  if (total_elems > MAX_THRESH)
+    {
+      char *lo = base_ptr;
+      char *hi = &lo[size * (total_elems - 1)];
+      stack_node stack[STACK_SIZE];
+      stack_node *top = stack + 1;
+
+      while (STACK_NOT_EMPTY)
+        {
+          char *left_ptr;
+          char *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. */
+
+          char *mid = lo + size * ((hi - lo) / size >> 1);
+
+          if ((*cmp) ((void *) mid, (void *) lo) < 0)
+            SWAP (mid, lo, size);
+          if ((*cmp) ((void *) hi, (void *) mid) < 0)
+            SWAP (mid, hi, size);
+          else
+            goto jump_over;
+          if ((*cmp) ((void *) mid, (void *) lo) < 0)
+            SWAP (mid, lo, size);
+        jump_over:;
+
+          left_ptr  = lo + size;
+          right_ptr = hi - size;
+
+          /* 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 ((*cmp) ((void *) left_ptr, (void *) mid) < 0)
+                left_ptr += size;
+
+              while ((*cmp) ((void *) mid, (void *) right_ptr) < 0)
+                right_ptr -= size;
+
+              if (left_ptr < right_ptr)
+                {
+                  SWAP (left_ptr, right_ptr, size);
+                  if (mid == left_ptr)
+                    mid = right_ptr;
+                  else if (mid == right_ptr)
+                    mid = left_ptr;
+                  left_ptr += size;
+                  right_ptr -= size;
+                }
+              else if (left_ptr == right_ptr)
+                {
+                  left_ptr += size;
+                  right_ptr -= size;
+                  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 ((size_t) (right_ptr - lo) <= max_thresh)
+            {
+              if ((size_t) (hi - left_ptr) <= max_thresh)
+                /* Ignore both small partitions. */
+                POP (lo, hi);
+              else
+                /* Ignore small left partition. */
+                lo = left_ptr;
+            }
+          else if ((size_t) (hi - left_ptr) <= max_thresh)
+            /* Ignore small right partition. */
+            hi = right_ptr;
+          else if ((right_ptr - lo) > (hi - left_ptr))
+            {
+              /* Push larger left partition indices. */
+              PUSH (lo, right_ptr);
+              lo = left_ptr;
+            }
+          else
+            {
+              /* Push larger right partition indices. */
+              PUSH (left_ptr, hi);
+              hi = right_ptr;
+            }
+        }
+    }
+
+  /* Once the BASE_PTR 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_PTR 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!). */
+
+#define min(x, y) ((x) < (y) ? (x) : (y))
+
+  {
+    char *const end_ptr = &base_ptr[size * (total_elems - 1)];
+    char *tmp_ptr = base_ptr;
+    char *thresh = min(end_ptr, base_ptr + max_thresh);
+    register char *run_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 + size; run_ptr <= thresh; run_ptr += size)
+      if ((*cmp) ((void *) run_ptr, (void *) tmp_ptr) < 0)
+        tmp_ptr = run_ptr;
+
+    if (tmp_ptr != base_ptr)
+      SWAP (tmp_ptr, base_ptr, size);
+
+    /* Insertion sort, running from left-hand-side up to right-hand-side.  */
+
+    run_ptr = base_ptr + size;
+    while ((run_ptr += size) <= end_ptr)
+      {
+        tmp_ptr = run_ptr - size;
+        while ((*cmp) ((void *) run_ptr, (void *) tmp_ptr) < 0)
+          tmp_ptr -= size;
+
+        tmp_ptr += size;
+        if (tmp_ptr != run_ptr)
+          {
+            char *trav;
+
+            trav = run_ptr + size;
+            while (--trav >= run_ptr)
+              {
+                char c = *trav;
+                char *hi, *lo;
+
+                for (hi = lo = trav; (lo -= size) >= tmp_ptr; hi = lo)
+                  *hi = *lo;
+                *hi = c;
+              }
+          }
+      }
+  }
+}
+#endif