From a2cd100d71711b950beaf60ea7ddca4c77a70d59 Mon Sep 17 00:00:00 2001

From: Peter Jones <pjones@redhat.com>

Date: Fri, 9 Dec 2016 15:39:47 -0500

Subject: [PATCH] Add quicksort implementation

This will be used to sort the boot menu entries that are read from

the BootLoaderSpec config files.

---

 grub-core/kern/qsort.c | 279 +++++++++++++++++++++++++++++++++++++++++++++++++

 include/grub/misc.h    |  15 +++

 2 files changed, 294 insertions(+)

 create mode 100644 grub-core/kern/qsort.c

diff --git a/grub-core/kern/qsort.c b/grub-core/kern/qsort.c

new file mode 100644

index 00000000000..7f3fc9ffdae

--- /dev/null

+++ b/grub-core/kern/qsort.c

@@ -0,0 +1,279 @@

+/* quicksort

+ * This file from the GNU C Library.

+ * Copyright (C) 1991-2016 Free Software Foundation, Inc.

+ * Written by Douglas C. Schmidt (schmidt@ics.uci.edu).

+ *

+ *  GRUB  --  GRand Unified Bootloader

+ *

+ *  GRUB 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 3 of the License, or

+ *  (at your option) any later version.

+ *

+ *  GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.

+ */

+

+/* 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.  */

+

+#include <grub/types.h>

+#include <grub/misc.h>

+#include <grub/mm.h>

+

+#define CHAR_BIT 8

+

+/* Byte-wise swap two items of size SIZE. */

+#define SWAP(a, b, size)						      \

+  do									      \

+    {									      \

+      grub_size_t __size = (size);						      \

+      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 grub_size_t, we get as

+   upper bound for log (total_elements):

+   bits per byte (CHAR_BIT) * sizeof(grub_size_t).  */

+#define STACK_SIZE	(CHAR_BIT * sizeof(grub_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 grub_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)!  */

+

+void

+grub_qsort (void *const pbase, grub_size_t total_elems, grub_size_t size,

+	    grub_compar_d_fn_t cmp, void *arg)

+{

+  char *base_ptr = (char *) pbase;

+

+  const grub_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;

+

+      PUSH (NULL, NULL);

+

+      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, arg) < 0)

+	    SWAP (mid, lo, size);

+	  if ((*cmp) ((void *) hi, (void *) mid, arg) < 0)

+	    SWAP (mid, hi, size);

+	  else

+	    goto jump_over;

+	  if ((*cmp) ((void *) mid, (void *) lo, arg) < 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, arg) < 0)

+		left_ptr += size;

+

+	      while ((*cmp) ((void *) mid, (void *) right_ptr, arg) < 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 ((grub_size_t) (right_ptr - lo) <= max_thresh)

+            {

+              if ((grub_size_t) (hi - left_ptr) <= max_thresh)

+		/* Ignore both small partitions. */

+                POP (lo, hi);

+              else

+		/* Ignore small left partition. */

+                lo = left_ptr;

+            }

+          else if ((grub_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);

+    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, arg) < 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, arg) < 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;

+              }

+          }

+      }

+  }

+}

+

+void *

+grub_bsearch (const void *key, const void *base, grub_size_t nmemb, grub_size_t size,

+	 grub_compar_d_fn_t compar, void *state)

+{

+  grub_size_t l, u, idx;

+  const void *p;

+  int comparison;

+

+  l = 0;

+  u = nmemb;

+  while (l < u)

+    {

+      idx = (l + u) / 2;

+      p = (void *) (((const char *) base) + (idx * size));

+      comparison = (*compar) (key, p, state);

+      if (comparison < 0)

+	u = idx;

+      else if (comparison > 0)

+	l = idx + 1;

+      else

+	return (void *) p;

+    }

+

+  return NULL;

+}

diff --git a/include/grub/misc.h b/include/grub/misc.h

index 4737da1eaa9..3d55bafd64e 100644

--- a/include/grub/misc.h

+++ b/include/grub/misc.h

@@ -506,4 +506,19 @@ void EXPORT_FUNC(grub_real_boot_time) (const char *file,

 #define grub_max(a, b) (((a) > (b)) ? (a) : (b))

 #define grub_min(a, b) (((a) < (b)) ? (a) : (b))

+typedef int (*grub_compar_d_fn_t) (const void *p0, const void *p1, void *state);

+

+void *EXPORT_FUNC(grub_bsearch) (const void *key,

+			    const void *base,

+			    grub_size_t nmemb,

+			    grub_size_t size,

+			    grub_compar_d_fn_t compar,

+			    void *state);

+

+void EXPORT_FUNC(grub_qsort) (void *const pbase,

+			 grub_size_t total_elems,

+			 grub_size_t size,

+			 grub_compar_d_fn_t cmp,

+			 void *state);

+

 #endif /* ! GRUB_MISC_HEADER */