Viewing file:  isl_tarjan.c (3.92 KB) -rw-r--r--
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/*
* Copyright 2010-2011 INRIA Saclay
* Copyright 2012 Ecole Normale Superieure
*
* Use of this software is governed by the MIT license
*
* Written by Sven Verdoolaege, INRIA Saclay - Ile-de-France,
* Parc Club Orsay Universite, ZAC des vignes, 4 rue Jacques Monod,
* 91893 Orsay, France
* and Ecole Normale Superieure, 45 rue d’Ulm, 75230 Paris, France
*/
#include <stdlib.h>
#include <isl/ctx.h>
#include <isl_tarjan.h>
struct isl_tarjan_graph *isl_tarjan_graph_free(struct isl_tarjan_graph *g)
{
if (!g)
return NULL;
free(g->node);
free(g->stack);
free(g->order);
free(g);
return NULL;
}
static struct isl_tarjan_graph *isl_tarjan_graph_alloc(isl_ctx *ctx, int len)
{
struct isl_tarjan_graph *g;
int i;
g = isl_calloc_type(ctx, struct isl_tarjan_graph);
if (!g)
return NULL;
g->len = len;
g->node = isl_alloc_array(ctx, struct isl_tarjan_node, len);
if (len && !g->node)
goto error;
for (i = 0; i < len; ++i)
g->node[i].index = -1;
g->stack = isl_alloc_array(ctx, int, len);
if (len && !g->stack)
goto error;
g->order = isl_alloc_array(ctx, int, 2 * len);
if (len && !g->order)
goto error;
g->sp = 0;
g->index = 0;
g->op = 0;
return g;
error:
isl_tarjan_graph_free(g);
return NULL;
}
/* Perform Tarjan's algorithm for computing the strongly connected components
* in the graph with g->len nodes and with edges defined by "follows".
*/
static isl_stat isl_tarjan_components(struct isl_tarjan_graph *g, int i,
isl_bool (*follows)(int i, int j, void *user), void *user)
{
int j;
g->node[i].index = g->index;
g->node[i].min_index = g->index;
g->node[i].on_stack = 1;
g->index++;
g->stack[g->sp++] = i;
for (j = g->len - 1; j >= 0; --j) {
isl_bool f;
if (j == i)
continue;
if (g->node[j].index >= 0 &&
(!g->node[j].on_stack ||
g->node[j].index > g->node[i].min_index))
continue;
f = follows(i, j, user);
if (f < 0)
return isl_stat_error;
if (!f)
continue;
if (g->node[j].index < 0) {
isl_tarjan_components(g, j, follows, user);
if (g->node[j].min_index < g->node[i].min_index)
g->node[i].min_index = g->node[j].min_index;
} else if (g->node[j].index < g->node[i].min_index)
g->node[i].min_index = g->node[j].index;
}
if (g->node[i].index != g->node[i].min_index)
return isl_stat_ok;
do {
j = g->stack[--g->sp];
g->node[j].on_stack = 0;
g->order[g->op++] = j;
} while (j != i);
g->order[g->op++] = -1;
return isl_stat_ok;
}
/* Decompose the graph with "len" nodes and edges defined by "follows"
* into strongly connected components (SCCs).
* follows(i, j, user) should return 1 if "i" follows "j" and 0 otherwise.
* It should return -1 on error.
*
* If SCC a contains a node i that follows a node j in another SCC b
* (i.e., follows(i, j, user) returns 1), then SCC a will appear after SCC b
* in the result.
*/
struct isl_tarjan_graph *isl_tarjan_graph_init(isl_ctx *ctx, int len,
isl_bool (*follows)(int i, int j, void *user), void *user)
{
int i;
struct isl_tarjan_graph *g = NULL;
g = isl_tarjan_graph_alloc(ctx, len);
if (!g)
return NULL;
for (i = len - 1; i >= 0; --i) {
if (g->node[i].index >= 0)
continue;
if (isl_tarjan_components(g, i, follows, user) < 0)
return isl_tarjan_graph_free(g);
}
return g;
}
/* Decompose the graph with "len" nodes and edges defined by "follows"
* into the strongly connected component (SCC) that contains "node"
* as well as all SCCs that are followed by this SCC.
* follows(i, j, user) should return 1 if "i" follows "j" and 0 otherwise.
* It should return -1 on error.
*
* The SCC containing "node" will appear as the last component
* in g->order.
*/
struct isl_tarjan_graph *isl_tarjan_graph_component(isl_ctx *ctx, int len,
int node, isl_bool (*follows)(int i, int j, void *user), void *user)
{
struct isl_tarjan_graph *g;
g = isl_tarjan_graph_alloc(ctx, len);
if (!g)
return NULL;
if (isl_tarjan_components(g, node, follows, user) < 0)
return isl_tarjan_graph_free(g);
return g;
}
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