Import list_sort from the Linux kernel

Makefile

@@ -41,7 +41,8 @@ OBJS := qtest.o report.o console.o harness.o queue.o \
         random.o dudect/constant.o dudect/fixture.o dudect/ttest.o \
         shannon_entropy.o \
         linenoise.o web.o \
-		shuffle.o
+		shuffle.o         \
+		list_sort.o
 
 deps := $(OBJS:%.o=.%.o.d)
 

list_sort.c

@@ -0,0 +1,257 @@
+// SPDX-License-Identifier: GPL-2.0
+// #include <linux/kernel.h>
+// #include <linux/bug.h>
+// #include <linux/compiler.h>
+// #include <linux/export.h>
+// #include <linux/string.h>
+// #include <linux/list_sort.h>
+#include "list_sort.h"
+
+/*
+ * Returns a list organized in an intermediate format suited
+ * to chaining of merge() calls: null-terminated, no reserved or
+ * sentinel head node, "prev" links not maintained.
+ */
+__attribute__((nonnull(2, 3, 4))) static struct list_head *
+merge(void *priv, list_cmp_func_t cmp, struct list_head *a, struct list_head *b)
+{
+    // cppcheck-suppress unassignedVariable
+    struct list_head *head, **tail = &head;
+
+    for (;;) {
+        /* if equal, take 'a' -- important for sort stability */
+        if (cmp(priv, a, b) <= 0) {
+            *tail = a;
+            tail = &a->next;
+            a = a->next;
+            if (!a) {
+                *tail = b;
+                break;
+            }
+        } else {
+            *tail = b;
+            tail = &b->next;
+            b = b->next;
+            if (!b) {
+                *tail = a;
+                break;
+            }
+        }
+    }
+    return head;
+}
+
+/*
+ * Combine final list merge with restoration of standard doubly-linked
+ * list structure.  This approach duplicates code from merge(), but
+ * runs faster than the tidier alternatives of either a separate final
+ * prev-link restoration pass, or maintaining the prev links
+ * throughout.
+ */
+__attribute__((nonnull(2, 3, 4, 5))) static void merge_final(
+    void *priv,
+    list_cmp_func_t cmp,
+    struct list_head *head,
+    struct list_head *a,
+    struct list_head *b)
+{
+    struct list_head *tail = head;
+    uint8_t count = 0;
+
+    for (;;) {
+        /* if equal, take 'a' -- important for sort stability */
+        if (cmp(priv, a, b) <= 0) {
+            tail->next = a;
+            a->prev = tail;
+            tail = a;
+            a = a->next;
+            if (!a)
+                break;
+        } else {
+            tail->next = b;
+            b->prev = tail;
+            tail = b;
+            b = b->next;
+            if (!b) {
+                b = a;
+                break;
+            }
+        }
+    }
+
+    /* Finish linking remainder of list b on to tail */
+    tail->next = b;
+    do {
+        /*
+         * If the merge is highly unbalanced (e.g. the input is
+         * already sorted), this loop may run many iterations.
+         * Continue callbacks to the client even though no
+         * element comparison is needed, so the client's cmp()
+         * routine can invoke cond_resched() periodically.
+         */
+        if (unlikely(!++count))
+            cmp(priv, b, b);
+        b->prev = tail;
+        tail = b;
+        b = b->next;
+    } while (b);
+
+    /* And the final links to make a circular doubly-linked list */
+    tail->next = head;
+    head->prev = tail;
+}
+
+/**
+ * list_sort - sort a list
+ * @priv: private data, opaque to list_sort(), passed to @cmp
+ * @head: the list to sort
+ * @cmp: the elements comparison function
+ *
+ * The comparison function @cmp must return > 0 if @a should sort after
+ * @b ("@a > @b" if you want an ascending sort), and <= 0 if @a should
+ * sort before @b *or* their original order should be preserved.  It is
+ * always called with the element that came first in the input in @a,
+ * and list_sort is a stable sort, so it is not necessary to distinguish
+ * the @a < @b and @a == @b cases.
+ *
+ * This is compatible with two styles of @cmp function:
+ * - The traditional style which returns <0 / =0 / >0, or
+ * - Returning a boolean 0/1.
+ * The latter offers a chance to save a few cycles in the comparison
+ * (which is used by e.g. plug_ctx_cmp() in block/blk-mq.c).
+ *
+ * A good way to write a multi-word comparison is::
+ *
+ *	if (a->high != b->high)
+ *		return a->high > b->high;
+ *	if (a->middle != b->middle)
+ *		return a->middle > b->middle;
+ *	return a->low > b->low;
+ *
+ *
+ * This mergesort is as eager as possible while always performing at least
+ * 2:1 balanced merges.  Given two pending sublists of size 2^k, they are
+ * merged to a size-2^(k+1) list as soon as we have 2^k following elements.
+ *
+ * Thus, it will avoid cache thrashing as long as 3*2^k elements can
+ * fit into the cache.  Not quite as good as a fully-eager bottom-up
+ * mergesort, but it does use 0.2*n fewer comparisons, so is faster in
+ * the common case that everything fits into L1.
+ *
+ *
+ * The merging is controlled by "count", the number of elements in the
+ * pending lists.  This is beautifully simple code, but rather subtle.
+ *
+ * Each time we increment "count", we set one bit (bit k) and clear
+ * bits k-1 .. 0.  Each time this happens (except the very first time
+ * for each bit, when count increments to 2^k), we merge two lists of
+ * size 2^k into one list of size 2^(k+1).
+ *
+ * This merge happens exactly when the count reaches an odd multiple of
+ * 2^k, which is when we have 2^k elements pending in smaller lists,
+ * so it's safe to merge away two lists of size 2^k.
+ *
+ * After this happens twice, we have created two lists of size 2^(k+1),
+ * which will be merged into a list of size 2^(k+2) before we create
+ * a third list of size 2^(k+1), so there are never more than two pending.
+ *
+ * The number of pending lists of size 2^k is determined by the
+ * state of bit k of "count" plus two extra pieces of information:
+ *
+ * - The state of bit k-1 (when k == 0, consider bit -1 always set), and
+ * - Whether the higher-order bits are zero or non-zero (i.e.
+ *   is count >= 2^(k+1)).
+ *
+ * There are six states we distinguish.  "x" represents some arbitrary
+ * bits, and "y" represents some arbitrary non-zero bits:
+ * 0:  00x: 0 pending of size 2^k;           x pending of sizes < 2^k
+ * 1:  01x: 0 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k
+ * 2: x10x: 0 pending of size 2^k; 2^k     + x pending of sizes < 2^k
+ * 3: x11x: 1 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k
+ * 4: y00x: 1 pending of size 2^k; 2^k     + x pending of sizes < 2^k
+ * 5: y01x: 2 pending of size 2^k; 2^(k-1) + x pending of sizes < 2^k
+ * (merge and loop back to state 2)
+ *
+ * We gain lists of size 2^k in the 2->3 and 4->5 transitions (because
+ * bit k-1 is set while the more significant bits are non-zero) and
+ * merge them away in the 5->2 transition.  Note in particular that just
+ * before the 5->2 transition, all lower-order bits are 11 (state 3),
+ * so there is one list of each smaller size.
+ *
+ * When we reach the end of the input, we merge all the pending
+ * lists, from smallest to largest.  If you work through cases 2 to
+ * 5 above, you can see that the number of elements we merge with a list
+ * of size 2^k varies from 2^(k-1) (cases 3 and 5 when x == 0) to
+ * 2^(k+1) - 1 (second merge of case 5 when x == 2^(k-1) - 1).
+ */
+__attribute__((nonnull(2, 3))) void list_sort(void *priv,
+                                              struct list_head *head,
+                                              list_cmp_func_t cmp)
+{
+    struct list_head *list = head->next, *pending = NULL;
+    size_t count = 0; /* Count of pending */
+
+    if (list == head->prev) /* Zero or one elements */
+        return;
+
+    /* Convert to a null-terminated singly-linked list. */
+    head->prev->next = NULL;
+
+    /*
+     * Data structure invariants:
+     * - All lists are singly linked and null-terminated; prev
+     *   pointers are not maintained.
+     * - pending is a prev-linked "list of lists" of sorted
+     *   sublists awaiting further merging.
+     * - Each of the sorted sublists is power-of-two in size.
+     * - Sublists are sorted by size and age, smallest & newest at front.
+     * - There are zero to two sublists of each size.
+     * - A pair of pending sublists are merged as soon as the number
+     *   of following pending elements equals their size (i.e.
+     *   each time count reaches an odd multiple of that size).
+     *   That ensures each later final merge will be at worst 2:1.
+     * - Each round consists of:
+     *   - Merging the two sublists selected by the highest bit
+     *     which flips when count is incremented, and
+     *   - Adding an element from the input as a size-1 sublist.
+     */
+    do {
+        size_t bits;
+        struct list_head **tail = &pending;
+
+        /* Find the least-significant clear bit in count */
+        for (bits = count; bits & 1; bits >>= 1)
+            tail = &(*tail)->prev;
+        /* Do the indicated merge */
+        if (likely(bits)) {
+            struct list_head *a = *tail, *b = a->prev;
+
+            a = merge(priv, cmp, b, a);
+            /* Install the merged result in place of the inputs */
+            a->prev = b->prev;
+            *tail = a;
+        }
+
+        /* Move one element from input list to pending */
+        list->prev = pending;
+        pending = list;
+        list = list->next;
+        pending->next = NULL;
+        count++;
+    } while (list);
+
+    /* End of input; merge together all the pending lists. */
+    list = pending;
+    pending = pending->prev;
+    for (;;) {
+        struct list_head *next = pending->prev;
+
+        if (!next)
+            break;
+        list = merge(priv, cmp, pending, list);
+        pending = next;
+    }
+    /* The final merge, rebuilding prev links */
+    merge_final(priv, cmp, head, pending, list);
+}
+// EXPORT_SYMBOL(list_sort);

list_sort.h

@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_LIST_SORT_H
+#define _LINUX_LIST_SORT_H
+
+#include "list.h"
+#include "stdint.h"
+
+// likely and unlikely are define in compiler.h
+#define likely(x) __builtin_expect(!!(x), 1)
+#define unlikely(x) __builtin_expect(!!(x), 0)
+
+// struct list_head;
+
+typedef int
+    __attribute__((nonnull(2, 3))) (*list_cmp_func_t)(void *,
+                                                      const struct list_head *,
+                                                      const struct list_head *);
+
+__attribute__((nonnull(2, 3))) void list_sort(void *priv,
+                                              struct list_head *head,
+                                              list_cmp_func_t cmp);
+#endif

qtest.c

@@ -21,6 +21,7 @@
 
 #include "dudect/fixture.h"
 #include "list.h"
+#include "list_sort.h"
 #include "random.h"
 #include "shuffle.h"
 
@@ -580,6 +581,63 @@ static bool do_size(int argc, char *argv[])
     return ok && !error_check();
 }
 
+int cmp(void *priv, const struct list_head *a, const struct list_head *b)
+{
+    element_t *a_ele = list_entry(a, element_t, list);  // get mother element
+    element_t *b_ele = list_entry(b, element_t, list);
+    return strcmp(a_ele->value, b_ele->value) < 0 ? 0 : 1;
+}
+
+bool do_lsort(int argc, char *argv[])
+{
+    if (argc != 1) {
+        report(1, "%s takes no arguments", argv[0]);
+        return false;
+    }
+
+    int cnt = 0;
+    if (!current || !current->q)
+        report(3, "Warning: Calling sort on null queue");
+    else
+        cnt = q_size(current->q);
+    error_check();
+
+    if (cnt < 2)
+        report(3, "Warning: Calling sort on single node");
+    error_check();
+
+    set_noallocate_mode(true);
+    if (current && exception_setup(true))
+        list_sort(NULL, current->q, cmp);
+    exception_cancel();
+    set_noallocate_mode(false);
+
+    bool ok = true;
+    if (current && current->size) {
+        for (struct list_head *cur_l = current->q->next;
+             cur_l != current->q && --cnt; cur_l = cur_l->next) {
+            /* Ensure each element in ascending/descending order */
+            element_t *item, *next_item;
+            item = list_entry(cur_l, element_t, list);
+            next_item = list_entry(cur_l->next, element_t, list);
+            if (!descend && strcmp(item->value, next_item->value) > 0) {
+                report(1, "ERROR: Not sorted in ascending order");
+                ok = false;
+                break;
+            }
+
+            if (descend && strcmp(item->value, next_item->value) < 0) {
+                report(1, "ERROR: Not sorted in descending order");
+                ok = false;
+                break;
+            }
+        }
+    }
+
+    q_show(3);
+    return ok && !error_check();
+}
+
 bool do_sort(int argc, char *argv[])
 {
     if (argc != 1) {
@@ -1066,6 +1124,7 @@ static void console_init()
     ADD_COMMAND(dedup, "Delete all nodes that have duplicate string", "");
     ADD_COMMAND(merge, "Merge all the queues into one sorted queue", "");
     ADD_COMMAND(shuffle, "shuffle the queues", "");
+    ADD_COMMAND(lsort, "Use Linux kernel sorting algorithm", "");
     ADD_COMMAND(swap, "Swap every two adjacent nodes in queue", "");
     ADD_COMMAND(ascend,
                 "Remove every node which has a node with a strictly less "

traces/trace-sort.cmd

@@ -0,0 +1,7 @@
+option fail 0
+option malloc 0
+new
+ih RAND 500000
+time
+sort
+time