/*
* Copyright (c) 2005, Jon Seymour
*
* For more information about epoch theory on which this module is based,
* refer to http://blackcubes.dyndns.org/epoch/. That web page defines
* terms such as "epoch" and "minimal, non-linear epoch" and provides rationales
* for some of the algorithms used here.
*
*/
#include
/* Provides arbitrary precision integers required to accurately represent
* fractional mass: */
#include
#include "cache.h"
#include "commit.h"
#include "epoch.h"
struct fraction {
BIGNUM numerator;
BIGNUM denominator;
};
#define HAS_EXACTLY_ONE_PARENT(n) ((n)->parents && !(n)->parents->next)
static BN_CTX *context = NULL;
static struct fraction *one = NULL;
static struct fraction *zero = NULL;
static BN_CTX *get_BN_CTX(void)
{
if (!context) {
context = BN_CTX_new();
}
return context;
}
static struct fraction *new_zero(void)
{
struct fraction *result = xmalloc(sizeof(*result));
BN_init(&result->numerator);
BN_init(&result->denominator);
BN_zero(&result->numerator);
BN_one(&result->denominator);
return result;
}
static void clear_fraction(struct fraction *fraction)
{
BN_clear(&fraction->numerator);
BN_clear(&fraction->denominator);
}
static struct fraction *divide(struct fraction *result, struct fraction *fraction, int divisor)
{
BIGNUM bn_divisor;
BN_init(&bn_divisor);
BN_set_word(&bn_divisor, divisor);
BN_copy(&result->numerator, &fraction->numerator);
BN_mul(&result->denominator, &fraction->denominator, &bn_divisor, get_BN_CTX());
BN_clear(&bn_divisor);
return result;
}
static struct fraction *init_fraction(struct fraction *fraction)
{
BN_init(&fraction->numerator);
BN_init(&fraction->denominator);
BN_zero(&fraction->numerator);
BN_one(&fraction->denominator);
return fraction;
}
static struct fraction *get_one(void)
{
if (!one) {
one = new_zero();
BN_one(&one->numerator);
}
return one;
}
static struct fraction *get_zero(void)
{
if (!zero) {
zero = new_zero();
}
return zero;
}
static struct fraction *copy(struct fraction *to, struct fraction *from)
{
BN_copy(&to->numerator, &from->numerator);
BN_copy(&to->denominator, &from->denominator);
return to;
}
static struct fraction *add(struct fraction *result, struct fraction *left, struct fraction *right)
{
BIGNUM a, b, gcd;
BN_init(&a);
BN_init(&b);
BN_init(&gcd);
BN_mul(&a, &left->numerator, &right->denominator, get_BN_CTX());
BN_mul(&b, &left->denominator, &right->numerator, get_BN_CTX());
BN_mul(&result->denominator, &left->denominator, &right->denominator, get_BN_CTX());
BN_add(&result->numerator, &a, &b);
BN_gcd(&gcd, &result->denominator, &result->numerator, get_BN_CTX());
BN_div(&result->denominator, NULL, &result->denominator, &gcd, get_BN_CTX());
BN_div(&result->numerator, NULL, &result->numerator, &gcd, get_BN_CTX());
BN_clear(&a);
BN_clear(&b);
BN_clear(&gcd);
return result;
}
static int compare(struct fraction *left, struct fraction *right)
{
BIGNUM a, b;
int result;
BN_init(&a);
BN_init(&b);
BN_mul(&a, &left->numerator, &right->denominator, get_BN_CTX());
BN_mul(&b, &left->denominator, &right->numerator, get_BN_CTX());
result = BN_cmp(&a, &b);
BN_clear(&a);
BN_clear(&b);
return result;
}
struct mass_counter {
struct fraction seen;
struct fraction pending;
};
static struct mass_counter *new_mass_counter(struct commit *commit, struct fraction *pending)
{
struct mass_counter *mass_counter = xmalloc(sizeof(*mass_counter));
memset(mass_counter, 0, sizeof(*mass_counter));
init_fraction(&mass_counter->seen);
init_fraction(&mass_counter->pending);
copy(&mass_counter->pending, pending);
copy(&mass_counter->seen, get_zero());
if (commit->object.util) {
die("multiple attempts to initialize mass counter for %s",
sha1_to_hex(commit->object.sha1));
}
commit->object.util = mass_counter;
return mass_counter;
}
static void free_mass_counter(struct mass_counter *counter)
{
clear_fraction(&counter->seen);
clear_fraction(&counter->pending);
free(counter);
}
/*
* Finds the base commit of a list of commits.
*
* One property of the commit being searched for is that every commit reachable
* from the base commit is reachable from the commits in the starting list only
* via paths that include the base commit.
*
* This algorithm uses a conservation of mass approach to find the base commit.
*
* We start by injecting one unit of mass into the graph at each
* of the commits in the starting list. Injecting mass into a commit
* is achieved by adding to its pending mass counter and, if it is not already
* enqueued, enqueuing the commit in a list of pending commits, in latest
* commit date first order.
*
* The algorithm then preceeds to visit each commit in the pending queue.
* Upon each visit, the pending mass is added to the mass already seen for that
* commit and then divided into N equal portions, where N is the number of
* parents of the commit being visited. The divided portions are then injected
* into each of the parents.
*
* The algorithm continues until we discover a commit which has seen all the
* mass originally injected or until we run out of things to do.
*
* If we find a commit that has seen all the original mass, we have found
* the common base of all the commits in the starting list.
*
* The algorithm does _not_ depend on accurate timestamps for correct operation.
* However, reasonably sane (e.g. non-random) timestamps are required in order
* to prevent an exponential performance characteristic. The occasional
* timestamp inaccuracy will not dramatically affect performance but may
* result in more nodes being processed than strictly necessary.
*
* This procedure sets *boundary to the address of the base commit. It returns
* non-zero if, and only if, there was a problem parsing one of the
* commits discovered during the traversal.
*/
static int find_base_for_list(struct commit_list *list, struct commit **boundary)
{
int ret = 0;
struct commit_list *cleaner = NULL;
struct commit_list *pending = NULL;
struct fraction injected;
init_fraction(&injected);
*boundary = NULL;
for (; list; list = list->next) {
struct commit *item = list->item;
if (!item->object.util) {
new_mass_counter(list->item, get_one());
add(&injected, &injected, get_one());
commit_list_insert(list->item, &cleaner);
commit_list_insert(list->item, &pending);
}
}
while (!*boundary && pending && !ret) {
struct commit *latest = pop_commit(&pending);
struct mass_counter *latest_node = (struct mass_counter *) latest->object.util;
int num_parents;
if ((ret = parse_commit(latest)))
continue;
add(&latest_node->seen, &latest_node->seen, &latest_node->pending);
num_parents = count_parents(latest);
if (num_parents) {
struct fraction distribution;
struct commit_list *parents;
divide(init_fraction(&distribution), &latest_node->pending, num_parents);
for (parents = latest->parents; parents; parents = parents->next) {
struct commit *parent = parents->item;
struct mass_counter *parent_node = (struct mass_counter *) parent->object.util;
if (!parent_node) {
parent_node = new_mass_counter(parent, &distribution);
insert_by_date(parent, &pending);
commit_list_insert(parent, &cleaner);
} else {
if (!compare(&parent_node->pending, get_zero()))
insert_by_date(parent, &pending);
add(&parent_node->pending, &parent_node->pending, &distribution);
}
}
clear_fraction(&distribution);
}
if (!compare(&latest_node->seen, &injected))
*boundary = latest;
copy(&latest_node->pending, get_zero());
}
while (cleaner) {
struct commit *next = pop_commit(&cleaner);
free_mass_counter((struct mass_counter *) next->object.util);
next->object.util = NULL;
}
if (pending)
free_commit_list(pending);
clear_fraction(&injected);
return ret;
}
/*
* Finds the base of an minimal, non-linear epoch, headed at head, by
* applying the find_base_for_list to a list consisting of the parents
*/
static int find_base(struct commit *head, struct commit **boundary)
{
int ret = 0;
struct commit_list *pending = NULL;
struct commit_list *next;
for (next = head->parents; next; next = next->next) {
commit_list_insert(next->item, &pending);
}
ret = find_base_for_list(pending, boundary);
free_commit_list(pending);
return ret;
}
/*
* This procedure traverses to the boundary of the first epoch in the epoch
* sequence of the epoch headed at head_of_epoch. This is either the end of
* the maximal linear epoch or the base of a minimal non-linear epoch.
*
* The queue of pending nodes is sorted in reverse date order and each node
* is currently in the queue at most once.
*/
static int find_next_epoch_boundary(struct commit *head_of_epoch, struct commit **boundary)
{
int ret;
struct commit *item = head_of_epoch;
ret = parse_commit(item);
if (ret)
return ret;
if (HAS_EXACTLY_ONE_PARENT(item)) {
/*
* We are at the start of a maximimal linear epoch.
* Traverse to the end.
*/
while (HAS_EXACTLY_ONE_PARENT(item) && !ret) {
item = item->parents->item;
ret = parse_commit(item);
}
*boundary = item;
} else {
/*
* Otherwise, we are at the start of a minimal, non-linear
* epoch - find the common base of all parents.
*/
ret = find_base(item, boundary);
}
return ret;
}
/*
* Returns non-zero if parent is known to be a parent of child.
*/
static int is_parent_of(struct commit *parent, struct commit *child)
{
struct commit_list *parents;
for (parents = child->parents; parents; parents = parents->next) {
if (!memcmp(parent->object.sha1, parents->item->object.sha1,
sizeof(parents->item->object.sha1)))
return 1;
}
return 0;
}
/*
* Pushes an item onto the merge order stack. If the top of the stack is
* marked as being a possible "break", we check to see whether it actually
* is a break.
*/
static void push_onto_merge_order_stack(struct commit_list **stack, struct commit *item)
{
struct commit_list *top = *stack;
if (top && (top->item->object.flags & DISCONTINUITY)) {
if (is_parent_of(top->item, item)) {
top->item->object.flags &= ~DISCONTINUITY;
}
}
commit_list_insert(item, stack);
}
/*
* Marks all interesting, visited commits reachable from this commit
* as uninteresting. We stop recursing when we reach the epoch boundary,
* an unvisited node or a node that has already been marking uninteresting.
*
* This doesn't actually mark all ancestors between the start node and the
* epoch boundary uninteresting, but does ensure that they will eventually
* be marked uninteresting when the main sort_first_epoch() traversal
* eventually reaches them.
*/
static void mark_ancestors_uninteresting(struct commit *commit)
{
unsigned int flags = commit->object.flags;
int visited = flags & VISITED;
int boundary = flags & BOUNDARY;
int uninteresting = flags & UNINTERESTING;
struct commit_list *next;
commit->object.flags |= UNINTERESTING;
/*
* We only need to recurse if
* we are not on the boundary and
* we have not already been marked uninteresting and
* we have already been visited.
*
* The main sort_first_epoch traverse will mark unreachable
* all uninteresting, unvisited parents as they are visited
* so there is no need to duplicate that traversal here.
*
* Similarly, if we are already marked uninteresting
* then either all ancestors have already been marked
* uninteresting or will be once the sort_first_epoch
* traverse reaches them.
*/
if (uninteresting || boundary || !visited)
return;
for (next = commit->parents; next; next = next->next)
mark_ancestors_uninteresting(next->item);
}
/*
* Sorts the nodes of the first epoch of the epoch sequence of the epoch headed at head
* into merge order.
*/
static void sort_first_epoch(struct commit *head, struct commit_list **stack)
{
struct commit_list *parents;
head->object.flags |= VISITED;
/*
* TODO: By sorting the parents in a different order, we can alter the
* merge order to show contemporaneous changes in parallel branches
* occurring after "local" changes. This is useful for a developer
* when a developer wants to see all changes that were incorporated
* into the same merge as her own changes occur after her own
* changes.
*/
for (parents = head->parents; parents; parents = parents->next) {
struct commit *parent = parents->item;
if (head->object.flags & UNINTERESTING) {
/*
* Propagates the uninteresting bit to all parents.
* if we have already visited this parent, then
* the uninteresting bit will be propagated to each
* reachable commit that is still not marked
* uninteresting and won't otherwise be reached.
*/
mark_ancestors_uninteresting(parent);
}
if (!(parent->object.flags & VISITED)) {
if (parent->object.flags & BOUNDARY) {
if (*stack) {
die("something else is on the stack - %s",
sha1_to_hex((*stack)->item->object.sha1));
}
push_onto_merge_order_stack(stack, parent);
parent->object.flags |= VISITED;
} else {
sort_first_epoch(parent, stack);
if (parents) {
/*
* This indicates a possible
* discontinuity it may not be be
* actual discontinuity if the head
* of parent N happens to be the tail
* of parent N+1.
*
* The next push onto the stack will
* resolve the question.
*/
(*stack)->item->object.flags |= DISCONTINUITY;
}
}
}
}
push_onto_merge_order_stack(stack, head);
}
/*
* Emit the contents of the stack.
*
* The stack is freed and replaced by NULL.
*
* Sets the return value to STOP if no further output should be generated.
*/
static int emit_stack(struct commit_list **stack, emitter_func emitter, int include_last)
{
unsigned int seen = 0;
int action = CONTINUE;
while (*stack && (action != STOP)) {
struct commit *next = pop_commit(stack);
seen |= next->object.flags;
if (*stack || include_last) {
if (!*stack)
next->object.flags |= BOUNDARY;
action = emitter(next);
}
}
if (*stack) {
free_commit_list(*stack);
*stack = NULL;
}
return (action == STOP || (seen & UNINTERESTING)) ? STOP : CONTINUE;
}
/*
* Sorts an arbitrary epoch into merge order by sorting each epoch
* of its epoch sequence into order.
*
* Note: this algorithm currently leaves traces of its execution in the
* object flags of nodes it discovers. This should probably be fixed.
*/
static int sort_in_merge_order(struct commit *head_of_epoch, emitter_func emitter)
{
struct commit *next = head_of_epoch;
int ret = 0;
int action = CONTINUE;
ret = parse_commit(head_of_epoch);
next->object.flags |= BOUNDARY;
while (next && next->parents && !ret && (action != STOP)) {
struct commit *base = NULL;
ret = find_next_epoch_boundary(next, &base);
if (ret)
return ret;
next->object.flags |= BOUNDARY;
if (base)
base->object.flags |= BOUNDARY;
if (HAS_EXACTLY_ONE_PARENT(next)) {
while (HAS_EXACTLY_ONE_PARENT(next)
&& (action != STOP)
&& !ret) {
if (next->object.flags & UNINTERESTING) {
action = STOP;
} else {
action = emitter(next);
}
if (action != STOP) {
next = next->parents->item;
ret = parse_commit(next);
}
}
} else {
struct commit_list *stack = NULL;
sort_first_epoch(next, &stack);
action = emit_stack(&stack, emitter, (base == NULL));
next = base;
}
}
if (next && (action != STOP) && !ret) {
emitter(next);
}
return ret;
}
/*
* Sorts the nodes reachable from a starting list in merge order, we
* first find the base for the starting list and then sort all nodes
* in this subgraph using the sort_first_epoch algorithm. Once we have
* reached the base we can continue sorting using sort_in_merge_order.
*/
int sort_list_in_merge_order(struct commit_list *list, emitter_func emitter)
{
struct commit_list *stack = NULL;
struct commit *base;
int ret = 0;
int action = CONTINUE;
struct commit_list *reversed = NULL;
for (; list; list = list->next)
commit_list_insert(list->item, &reversed);
if (!reversed)
return ret;
else if (!reversed->next) {
/*
* If there is only one element in the list, we can sort it
* using sort_in_merge_order.
*/
base = reversed->item;
} else {
/*
* Otherwise, we search for the base of the list.
*/
ret = find_base_for_list(reversed, &base);
if (ret)
return ret;
if (base)
base->object.flags |= BOUNDARY;
while (reversed) {
struct commit * next = pop_commit(&reversed);
if (!(next->object.flags & VISITED) && next!=base) {
sort_first_epoch(next, &stack);
if (reversed) {
/*
* If we have more commits
* to push, then the first
* push for the next parent may
* (or may * not) represent a
* discontinuity with respect
* to the parent currently on
* the top of the stack.
*
* Mark it for checking here,
* and check it with the next
* push. See sort_first_epoch()
* for more details.
*/
stack->item->object.flags |= DISCONTINUITY;
}
}
}
action = emit_stack(&stack, emitter, (base==NULL));
}
if (base && (action != STOP)) {
ret = sort_in_merge_order(base, emitter);
}
return ret;
}