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Fix the behaviour of sort_pm_map() (issue #392)

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The existing algorithm both read and wrote data beyond the end of the
array and, when moving data, moved it in the wrong direction. Replace
it with a bog-standard insertion sort algorithm. The resulting code
is smaller and probably faster, as memmove() is not in-lined.
This commit is contained in:
Martin Whitaker 2024-04-09 20:07:09 +01:00
parent 53ca89f8ae
commit 778c7b4cc4
1 changed files with 7 additions and 16 deletions
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23
system/pmem.c
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@ -1,5 +1,5 @@
// SPDX-License-Identifier: GPL-2.0 // SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2020-2022 Martin Whitaker. // Copyright (C) 2020-2024 Martin Whitaker.
// //
// Derived from memtest86+ memsize.c // Derived from memtest86+ memsize.c
// //
@ -225,23 +225,14 @@ static void init_pm_map(const e820_entry_t e820_map[], int e820_entries)
static void sort_pm_map(void) static void sort_pm_map(void)
{ {
// Do an insertion sort on the pm_map. On an already sorted list this should be a O(n) algorithm. // Do an insertion sort on the pm_map. On an already sorted list this should be a O(n) algorithm.
for (int i = 0; i < pm_map_size; i++) { for (int i = 1; i < pm_map_size; i++) {
// Find where to insert the current element. pm_map_t candidate = pm_map[i];
int j = i - 1; int j = i;
while (j >= 0) { while ((j > 0) && (pm_map[j-1].start > candidate.start)) {
if (pm_map[i].start > pm_map[j].start) { pm_map[j] = pm_map[j-1];
j++;
break;
}
j--; j--;
} }
// Insert the current element. pm_map[j] = candidate;
if (i != j) {
pm_map_t temp;
temp = pm_map[i];
memmove(&pm_map[j], &pm_map[j+1], (i - j) * sizeof(temp));
pm_map[j] = temp;
}
} }
} }