/*
* Copyright (C) the libgit2 contributors. All rights reserved.
*
* This file is part of libgit2, distributed under the GNU GPL v2 with
* a Linking Exception. For full terms see the included COPYING file.
*/
#include "common.h"
/**
* An array-of-pointers implementation of Python's Timsort
* Based on code by Christopher Swenson under the MIT license
*
* Copyright (c) 2010 Christopher Swenson
* Copyright (c) 2011 Vicent Marti
*/
#ifndef MAX
# define MAX(x,y) (((x) > (y) ? (x) : (y)))
#endif
#ifndef MIN
# define MIN(x,y) (((x) < (y) ? (x) : (y)))
#endif
static int binsearch(
void **dst, const void *x, size_t size, git__sort_r_cmp cmp, void *payload)
{
int l, c, r;
void *lx, *cx;
assert(size > 0);
l = 0;
r = (int)size - 1;
c = r >> 1;
lx = dst[l];
/* check for beginning conditions */
if (cmp(x, lx, payload) < 0)
return 0;
else if (cmp(x, lx, payload) == 0) {
int i = 1;
while (cmp(x, dst[i], payload) == 0)
i++;
return i;
}
/* guaranteed not to be >= rx */
cx = dst[c];
while (1) {
const int val = cmp(x, cx, payload);
if (val < 0) {
if (c - l <= 1) return c;
r = c;
} else if (val > 0) {
if (r - c <= 1) return c + 1;
l = c;
lx = cx;
} else {
do {
cx = dst[++c];
} while (cmp(x, cx, payload) == 0);
return c;
}
c = l + ((r - l) >> 1);
cx = dst[c];
}
}
/* Binary insertion sort, but knowing that the first "start" entries are sorted. Used in timsort. */
static void bisort(
void **dst, size_t start, size_t size, git__sort_r_cmp cmp, void *payload)
{
size_t i;
void *x;
int location;
for (i = start; i < size; i++) {
int j;
/* If this entry is already correct, just move along */
if (cmp(dst[i - 1], dst[i], payload) <= 0)
continue;
/* Else we need to find the right place, shift everything over, and squeeze in */
x = dst[i];
location = binsearch(dst, x, i, cmp, payload);
for (j = (int)i - 1; j >= location; j--) {
dst[j + 1] = dst[j];
}
dst[location] = x;
}
}
/* timsort implementation, based on timsort.txt */
struct tsort_run {
ssize_t start;
ssize_t length;
};
struct tsort_store {
size_t alloc;
git__sort_r_cmp cmp;
void *payload;
void **storage;
};
static void reverse_elements(void **dst, ssize_t start, ssize_t end)
{
while (start < end) {
void *tmp = dst[start];
dst[start] = dst[end];
dst[end] = tmp;
start++;
end--;
}
}
static ssize_t count_run(
void **dst, ssize_t start, ssize_t size, struct tsort_store *store)
{
ssize_t curr = start + 2;
if (size - start == 1)
return 1;
if (start >= size - 2) {
if (store->cmp(dst[size - 2], dst[size - 1], store->payload) > 0) {
void *tmp = dst[size - 1];
dst[size - 1] = dst[size - 2];
dst[size - 2] = tmp;
}
return 2;
}
if (store->cmp(dst[start], dst[start + 1], store->payload) <= 0) {
while (curr < size - 1 &&
store->cmp(dst[curr - 1], dst[curr], store->payload) <= 0)
curr++;
return curr - start;
} else {
while (curr < size - 1 &&
store->cmp(dst[curr - 1], dst[curr], store->payload) > 0)
curr++;
/* reverse in-place */
reverse_elements(dst, start, curr - 1);
return curr - start;
}
}
static size_t compute_minrun(size_t n)
{
int r = 0;
while (n >= 64) {
r |= n & 1;
n >>= 1;
}
return n + r;
}
static int check_invariant(struct tsort_run *stack, ssize_t stack_curr)
{
if (stack_curr < 2)
return 1;
else if (stack_curr == 2) {
const ssize_t A = stack[stack_curr - 2].length;
const ssize_t B = stack[stack_curr - 1].length;
return (A > B);
} else {
const ssize_t A = stack[stack_curr - 3].length;
const ssize_t B = stack[stack_curr - 2].length;
const ssize_t C = stack[stack_curr - 1].length;
return !((A <= B + C) || (B <= C));
}
}
static int resize(struct tsort_store *store, size_t new_size)
{
if (store->alloc < new_size) {
void **tempstore;
tempstore = git__reallocarray(store->storage, new_size, sizeof(void *));
/**
* Do not propagate on OOM; this will abort the sort and
* leave the array unsorted, but no error code will be
* raised
*/
if (tempstore == NULL)
return -1;
store->storage = tempstore;
store->alloc = new_size;
}
return 0;
}
static void merge(void **dst, const struct tsort_run *stack, ssize_t stack_curr, struct tsort_store *store)
{
const ssize_t A = stack[stack_curr - 2].length;
const ssize_t B = stack[stack_curr - 1].length;
const ssize_t curr = stack[stack_curr - 2].start;
void **storage;
ssize_t i, j, k;
if (resize(store, MIN(A, B)) < 0)
return;
storage = store->storage;
/* left merge */
if (A < B) {
memcpy(storage, &dst[curr], A * sizeof(void *));
i = 0;
j = curr + A;
for (k = curr; k < curr + A + B; k++) {
if ((i < A) && (j < curr + A + B)) {
if (store->cmp(storage[i], dst[j], store->payload) <= 0)
dst[k] = storage[i++];
else
dst[k] = dst[j++];
} else if (i < A) {
dst[k] = storage[i++];
} else
dst[k] = dst[j++];
}
} else {
memcpy(storage, &dst[curr + A], B * sizeof(void *));
i = B - 1;
j = curr + A - 1;
for (k = curr + A + B - 1; k >= curr; k--) {
if ((i >= 0) && (j >= curr)) {
if (store->cmp(dst[j], storage[i], store->payload) > 0)
dst[k] = dst[j--];
else
dst[k] = storage[i--];
} else if (i >= 0)
dst[k] = storage[i--];
else
dst[k] = dst[j--];
}
}
}
static ssize_t collapse(void **dst, struct tsort_run *stack, ssize_t stack_curr, struct tsort_store *store, ssize_t size)
{
ssize_t A, B, C;
while (1) {
/* if the stack only has one thing on it, we are done with the collapse */
if (stack_curr <= 1)
break;
/* if this is the last merge, just do it */
if ((stack_curr == 2) && (stack[0].length + stack[1].length == size)) {
merge(dst, stack, stack_curr, store);
stack[0].length += stack[1].length;
stack_curr--;
break;
}
/* check if the invariant is off for a stack of 2 elements */
else if ((stack_curr == 2) && (stack[0].length <= stack[1].length)) {
merge(dst, stack, stack_curr, store);
stack[0].length += stack[1].length;
stack_curr--;
break;
}
else if (stack_curr == 2)
break;
A = stack[stack_curr - 3].length;
B = stack[stack_curr - 2].length;
C = stack[stack_curr - 1].length;
/* check first invariant */
if (A <= B + C) {
if (A < C) {
merge(dst, stack, stack_curr - 1, store);
stack[stack_curr - 3].length += stack[stack_curr - 2].length;
stack[stack_curr - 2] = stack[stack_curr - 1];
stack_curr--;
} else {
merge(dst, stack, stack_curr, store);
stack[stack_curr - 2].length += stack[stack_curr - 1].length;
stack_curr--;
}
} else if (B <= C) {
merge(dst, stack, stack_curr, store);
stack[stack_curr - 2].length += stack[stack_curr - 1].length;
stack_curr--;
} else
break;
}
return stack_curr;
}
#define PUSH_NEXT() do {\
len = count_run(dst, curr, size, store);\
run = minrun;\
if (run < minrun) run = minrun;\
if (run > (ssize_t)size - curr) run = size - curr;\
if (run > len) {\
bisort(&dst[curr], len, run, cmp, payload);\
len = run;\
}\
run_stack[stack_curr].start = curr;\
run_stack[stack_curr++].length = len;\
curr += len;\
if (curr == (ssize_t)size) {\
/* finish up */ \
while (stack_curr > 1) { \
merge(dst, run_stack, stack_curr, store); \
run_stack[stack_curr - 2].length += run_stack[stack_curr - 1].length; \
stack_curr--; \
} \
if (store->storage != NULL) {\
git__free(store->storage);\
store->storage = NULL;\
}\
return;\
}\
}\
while (0)
void git__tsort_r(
void **dst, size_t size, git__sort_r_cmp cmp, void *payload)
{
struct tsort_store _store, *store = &_store;
struct tsort_run run_stack[128];
ssize_t stack_curr = 0;
ssize_t len, run;
ssize_t curr = 0;
ssize_t minrun;
if (size < 64) {
bisort(dst, 1, size, cmp, payload);
return;
}
/* compute the minimum run length */
minrun = (ssize_t)compute_minrun(size);
/* temporary storage for merges */
store->alloc = 0;
store->storage = NULL;
store->cmp = cmp;
store->payload = payload;
PUSH_NEXT();
PUSH_NEXT();
PUSH_NEXT();
while (1) {
if (!check_invariant(run_stack, stack_curr)) {
stack_curr = collapse(dst, run_stack, stack_curr, store, size);
continue;
}
PUSH_NEXT();
}
}
static int tsort_r_cmp(const void *a, const void *b, void *payload)
{
return ((git__tsort_cmp)payload)(a, b);
}
void git__tsort(void **dst, size_t size, git__tsort_cmp cmp)
{
git__tsort_r(dst, size, tsort_r_cmp, cmp);
}