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grub2/0268-Add-quicksort-implementation.patch
Peter Jones ad4aff0c12 Rework SB patches and 10_linux.in changes even harder. 
Apparently working on two identical trees at once is not good for doing things
right.

Resolves: rhbz#1601578
Signed-off-by: Peter Jones <pjones@redhat.com>
2018-07-17 10:21:37 -04:00

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From 0000000000000000000000000000000000000000 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 fcaf1201e39..cbfae75a1b4 100644
--- a/include/grub/misc.h
+++ b/include/grub/misc.h
@@ -507,4 +507,19 @@ 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 */
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