diff options
Diffstat (limited to 'epoch.c')
| -rw-r--r-- | epoch.c | 640 |
1 files changed, 0 insertions, 640 deletions
diff --git a/epoch.c b/epoch.c deleted file mode 100644 index 0f37492..0000000 --- a/epoch.c +++ /dev/null @@ -1,640 +0,0 @@ -/* - * 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 <stdlib.h> - -/* Provides arbitrary precision integers required to accurately represent - * fractional mass: */ -#include <openssl/bn.h> - -#include "cache.h" -#include "commit.h" -#include "revision.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 proceeds 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; -} |