/*      $NetBSD: nbperf-chm.c,v 1.5 2021/01/26 21:25:55 joerg Exp $     */
/*-
 * Copyright (c) 2009 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code is derived from software contributed to The NetBSD Foundation
 * by Joerg Sonnenberger.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
#if HAVE_NBTOOL_CONFIG_H
#include "nbtool_config.h"
#endif

#include <sys/cdefs.h>
__RCSID("$NetBSD: nbperf-chm.c,v 1.5 2021/01/26 21:25:55 joerg Exp $");

#include <err.h>
#include <inttypes.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#include "nbperf.h"

#include "graph2.h"

/*
 * A full description of the algorithm can be found in:
 * "An optimal algorithm for generating minimal perfect hash functions"
 * by Czech, Havas and Majewski in Information Processing Letters,
 * 43(5):256-264, October 1992.
 */

/*
 * The algorithm is based on random, acyclic graphs.
 *
 * Each edge in the represents a key.  The vertices are the reminder of
 * the hash function mod n.  n = cm with c > 2, otherwise the propability
 * of finding an acyclic graph is very low (for 2-graphs).  The constant
 * for 3-graphs is 1.24.
 *
 * After the hashing phase, the graph is checked for cycles.
 * A cycle-free graph is either empty or has a vertex of degree 1.
 * Removing the edge for this vertex doesn't change this property,
 * so applying this recursively reduces the size of the graph.
 * If the graph is empty at the end of the process, it was acyclic.
 *
 * The assignment step now sets g[i] := 0 and processes the edges
 * in reverse order of removal.  That ensures that at least one vertex
 * is always unvisited and can be assigned.
 */

struct state {
        struct SIZED(graph) graph;
        uint32_t *g;
        uint8_t *visited;
};

#if GRAPH_SIZE == 3
static void
assign_nodes(struct state *state)
{
        struct SIZED(edge) *e;
        size_t i;
        uint32_t e_idx, v0, v1, v2, g;

        for (i = 0; i < state->graph.e; ++i) {
                e_idx = state->graph.output_order[i];
                e = &state->graph.edges[e_idx];
                if (!state->visited[e->vertices[0]]) {
                        v0 = e->vertices[0];
                        v1 = e->vertices[1];
                        v2 = e->vertices[2];
                } else if (!state->visited[e->vertices[1]]) {
                        v0 = e->vertices[1];
                        v1 = e->vertices[0];
                        v2 = e->vertices[2];
                } else {
                        v0 = e->vertices[2];
                        v1 = e->vertices[0];
                        v2 = e->vertices[1];
                }
                g = e_idx - state->g[v1] - state->g[v2];
                if (g >= state->graph.e) {
                        g += state->graph.e;
                        if (g >= state->graph.e)
                                g += state->graph.e;
                }
                state->g[v0] = g;
                state->visited[v0] = 1;
                state->visited[v1] = 1;
                state->visited[v2] = 1;
        }
}
#else
static void
assign_nodes(struct state *state)
{
        struct SIZED(edge) *e;
        size_t i;
        uint32_t e_idx, v0, v1, g;

        for (i = 0; i < state->graph.e; ++i) {
                e_idx = state->graph.output_order[i];
                e = &state->graph.edges[e_idx];
                if (!state->visited[e->vertices[0]]) {
                        v0 = e->vertices[0];
                        v1 = e->vertices[1];
                } else {
                        v0 = e->vertices[1];
                        v1 = e->vertices[0];
                }
                g = e_idx - state->g[v1];
                if (g >= state->graph.e)
                        g += state->graph.e;
                state->g[v0] = g;
                state->visited[v0] = 1;
                state->visited[v1] = 1;
        }
}
#endif

static void
print_hash(struct nbperf *nbperf, struct state *state)
{
        uint32_t i, per_line;
        const char *g_type;
        int g_width;

        fprintf(nbperf->output, "#include <stdlib.h>\n\n");

        fprintf(nbperf->output, "%suint32_t\n",
            nbperf->static_hash ? "static " : "");
        fprintf(nbperf->output,
            "%s(const void * __restrict key, size_t keylen)\n",
            nbperf->hash_name);
        fprintf(nbperf->output, "{\n");
        if (state->graph.v >= 65536) {
                g_type = "uint32_t";
                g_width = 8;
                per_line = 4;
        } else if (state->graph.v >= 256) {
                g_type = "uint16_t";
                g_width = 4;
                per_line = 8;
        } else {
                g_type = "uint8_t";
                g_width = 2;
                per_line = 10;
        }
        fprintf(nbperf->output, "\tstatic const %s g[%" PRId32 "] = {\n",
            g_type, state->graph.v);
        for (i = 0; i < state->graph.v; ++i) {
                fprintf(nbperf->output, "%s0x%0*" PRIx32 ",%s",
                    (i % per_line == 0 ? "\t    " : " "),
                    g_width, state->g[i],
                    (i % per_line == per_line - 1 ? "\n" : ""));
        }
        if (i % per_line != 0)
                fprintf(nbperf->output, "\n\t};\n");
        else
                fprintf(nbperf->output, "\t};\n");
        fprintf(nbperf->output, "\tuint32_t h[%zu];\n\n", nbperf->hash_size);
        (*nbperf->print_hash)(nbperf, "\t", "key", "keylen", "h");

        fprintf(nbperf->output, "\n\th[0] = h[0] %% %" PRIu32 ";\n",
            state->graph.v);
        fprintf(nbperf->output, "\th[1] = h[1] %% %" PRIu32 ";\n",
            state->graph.v);
#if GRAPH_SIZE == 3
        fprintf(nbperf->output, "\th[2] = h[2] %% %" PRIu32 ";\n",
            state->graph.v);
#endif

        if (state->graph.hash_fudge & 1)
                fprintf(nbperf->output, "\th[1] ^= (h[0] == h[1]);\n");

#if GRAPH_SIZE == 3
        if (state->graph.hash_fudge & 2) {
                fprintf(nbperf->output,
                    "\th[2] ^= (h[0] == h[2] || h[1] == h[2]);\n");
                fprintf(nbperf->output,
                    "\th[2] ^= 2 * (h[0] == h[2] || h[1] == h[2]);\n");
        }
#endif

#if GRAPH_SIZE == 3
        fprintf(nbperf->output, "\treturn (g[h[0]] + g[h[1]] + g[h[2]]) %% "
            "%" PRIu32 ";\n", state->graph.e);
#else
        fprintf(nbperf->output, "\treturn (g[h[0]] + g[h[1]]) %% "
            "%" PRIu32 ";\n", state->graph.e);
#endif
        fprintf(nbperf->output, "}\n");

        if (nbperf->map_output != NULL) {
                for (i = 0; i < state->graph.e; ++i)
                        fprintf(nbperf->map_output, "%" PRIu32 "\n", i);
        }
}

int
#if GRAPH_SIZE == 3
chm3_compute(struct nbperf *nbperf)
#else
chm_compute(struct nbperf *nbperf)
#endif
{
        struct state state;
        int retval = -1;
        uint32_t v, e;

#if GRAPH_SIZE == 3
        if (nbperf->c == 0)
                nbperf-> c = 1.24;

        if (nbperf->c < 1.24)
                errx(1, "The argument for option -c must be at least 1.24");

        if (nbperf->hash_size < 3)
                errx(1, "The hash function must generate at least 3 values");
#else
        if (nbperf->c == 0)
                nbperf-> c = 2;

        if (nbperf->c < 2)
                errx(1, "The argument for option -c must be at least 2");

        if (nbperf->hash_size < 2)
                errx(1, "The hash function must generate at least 2 values");
#endif

        (*nbperf->seed_hash)(nbperf);
        e = nbperf->n;
        v = nbperf->c * nbperf->n;
#if GRAPH_SIZE == 3
        if (v == 1.24 * nbperf->n)
                ++v;
        if (v < 10)
                v = 10;
        if (nbperf->allow_hash_fudging)
                v = (v + 3) & ~3;
#else
        if (v == 2 * nbperf->n)
                ++v;
        if (nbperf->allow_hash_fudging)
                v = (v + 1) & ~1;
#endif

        state.g = calloc(sizeof(uint32_t), v);
        state.visited = calloc(sizeof(uint8_t), v);
        if (state.g == NULL || state.visited == NULL)
                err(1, "malloc failed");

        SIZED2(_setup)(&state.graph, v, e);
        if (SIZED2(_hash)(nbperf, &state.graph))
                goto failed;
        if (SIZED2(_output_order)(&state.graph))
                goto failed;
        assign_nodes(&state);
        print_hash(nbperf, &state);

        retval = 0;

failed:
        SIZED2(_free)(&state.graph);
        free(state.g);
        free(state.visited);
        return retval;
}