/*

 * Copyright 2022-2024 The OpenSSL Project Authors. All Rights Reserved.

 *

 * Licensed under the Apache License 2.0 (the "License").  You may not use

 * this file except in compliance with the License.  You can obtain a copy

 * in the file LICENSE in the source distribution or at

 * https://www.openssl.org/source/license.html

 */

#include <openssl/crypto.h>

#include <openssl/err.h>

#include <assert.h>

#include "internal/priority_queue.h"

#include "internal/safe_math.h"

#include "internal/numbers.h"

OSSL_SAFE_MATH_UNSIGNED(size_t, size_t)

/*

 * Fundamental operations:

 *                        Binary Heap   Fibonacci Heap

 *  Get smallest            O(1)          O(1)

 *  Delete any              O(log n)      O(log n) average but worst O(n)

 *  Insert                  O(log n)      O(1)

 *

 * Not supported:

 *  Merge two structures    O(log n)      O(1)

 *  Decrease key            O(log n)      O(1)

 *  Increase key            O(log n)      ?

 *

 * The Fibonacci heap is quite a bit more complicated to implement and has

 * larger overhead in practice.  We favour the binary heap here.  A multi-way

 * (ternary or quaternary) heap might elicit a performance advantage via better

 * cache access patterns.

 */

struct pq_heap_st {

    void *data;     /* User supplied data pointer */

    size_t index;   /* Constant index in elements[] */

};

struct pq_elem_st {

    size_t posn;    /* Current index in heap[] or link in free list */

#ifndef NDEBUG

    int used;       /* Debug flag indicating that this is in use */

#endif

};

struct ossl_pqueue_st {

    struct pq_heap_st *heap;

    struct pq_elem_st *elements;

    int (*compare)(const void *, const void *);

    size_t htop;        /* Highest used heap element */

    size_t hmax;        /* Allocated heap & element space */

    size_t freelist;    /* Index into elements[], start of free element list */

};

/*

 * The initial and maximum number of elements in the heap.

 */

static const size_t min_nodes = 8;

static const size_t max_nodes =

        SIZE_MAX / (sizeof(struct pq_heap_st) > sizeof(struct pq_elem_st)

                    ? sizeof(struct pq_heap_st) : sizeof(struct pq_elem_st));

#ifndef NDEBUG

/* Some basic sanity checking of the data structure */

# define ASSERT_USED(pq, idx)                                               \

    assert(pq->elements[pq->heap[idx].index].used);                         \

    assert(pq->elements[pq->heap[idx].index].posn == idx)

# define ASSERT_ELEM_USED(pq, elem)                                         \

    assert(pq->elements[elem].used)

#else

# define ASSERT_USED(pq, idx)

# define ASSERT_ELEM_USED(pq, elem)

#endif

/*

 * Calculate the array growth based on the target size.

 *

 * The growth factor is a rational number and is defined by a numerator

 * and a denominator.  According to Andrew Koenig in his paper "Why Are

 * Vectors Efficient?" from JOOP 11(5) 1998, this factor should be less

 * than the golden ratio (1.618...).

 *

 * We use an expansion factor of 8 / 5 = 1.6

 */

static ossl_inline size_t compute_pqueue_growth(size_t target, size_t current)

{

    int err = 0;

    while (current < target) {

        if (current >= max_nodes)

            return 0;

        current = safe_muldiv_size_t(current, 8, 5, &err);

        if (err)

            return 0;

        if (current >= max_nodes)

            current = max_nodes;

    }

    return current;

}

static ossl_inline void pqueue_swap_elem(OSSL_PQUEUE *pq, size_t i, size_t j)

{

    struct pq_heap_st *h = pq->heap, t_h;

    struct pq_elem_st *e = pq->elements;

    ASSERT_USED(pq, i);

    ASSERT_USED(pq, j);

    t_h = h[i];

    h[i] = h[j];

    h[j] = t_h;

    e[h[i].index].posn = i;

    e[h[j].index].posn = j;

}

static ossl_inline void pqueue_move_elem(OSSL_PQUEUE *pq, size_t from, size_t to)

{

    struct pq_heap_st *h = pq->heap;

    struct pq_elem_st *e = pq->elements;

    ASSERT_USED(pq, from);

    h[to] = h[from];

    e[h[to].index].posn = to;

}

/*

 * Force the specified element to the front of the heap.  This breaks

 * the heap partial ordering pre-condition.

 */

static ossl_inline void pqueue_force_bottom(OSSL_PQUEUE *pq, size_t n)

{

    ASSERT_USED(pq, n);

    while (n > 0) {

        const size_t p = (n - 1) / 2;

        ASSERT_USED(pq, p);

        pqueue_swap_elem(pq, n, p);

        n = p;

    }

}

/*

 * Move an element down to its correct position to restore the partial

 * order pre-condition.

 */

static ossl_inline void pqueue_move_down(OSSL_PQUEUE *pq, size_t n)

{

    struct pq_heap_st *h = pq->heap;

    ASSERT_USED(pq, n);

    while (n > 0) {

        const size_t p = (n - 1) / 2;

        ASSERT_USED(pq, p);

        if (pq->compare(h[n].data, h[p].data) >= 0)

            break;

        pqueue_swap_elem(pq, n, p);

        n = p;

    }

}

/*

 * Move an element up to its correct position to restore the partial

 * order pre-condition.

 */

static ossl_inline void pqueue_move_up(OSSL_PQUEUE *pq, size_t n)

{

    struct pq_heap_st *h = pq->heap;

    size_t p = n * 2 + 1;

    ASSERT_USED(pq, n);

    if (pq->htop > p + 1) {

        ASSERT_USED(pq, p);

        ASSERT_USED(pq, p + 1);

        if (pq->compare(h[p].data, h[p + 1].data) > 0)

            p++;

    }

    while (pq->htop > p && pq->compare(h[p].data, h[n].data) < 0) {

        ASSERT_USED(pq, p);

        pqueue_swap_elem(pq, n, p);

        n = p;

        p = n * 2 + 1;

        if (pq->htop > p + 1) {

            ASSERT_USED(pq, p + 1);

            if (pq->compare(h[p].data, h[p + 1].data) > 0)

                p++;

        }

    }

}

int ossl_pqueue_push(OSSL_PQUEUE *pq, void *data, size_t *elem)

{

    size_t n, m;

    if (!ossl_pqueue_reserve(pq, 1))

        return 0;

    n = pq->htop++;

    m = pq->freelist;

    pq->freelist = pq->elements[m].posn;

    pq->heap[n].data = data;

    pq->heap[n].index = m;

    pq->elements[m].posn = n;

#ifndef NDEBUG

    pq->elements[m].used = 1;

#endif

    pqueue_move_down(pq, n);

    if (elem != NULL)

        *elem = m;

    return 1;

}

void *ossl_pqueue_peek(const OSSL_PQUEUE *pq)

{

    if (pq->htop > 0) {

        ASSERT_USED(pq, 0);

        return pq->heap->data;

    }

    return NULL;

}

void *ossl_pqueue_pop(OSSL_PQUEUE *pq)

{

    void *res;

    size_t elem;

    if (pq == NULL || pq->htop == 0)

        return NULL;

    ASSERT_USED(pq, 0);

    res = pq->heap->data;

    elem = pq->heap->index;

    if (--pq->htop != 0) {

        pqueue_move_elem(pq, pq->htop, 0);

        pqueue_move_up(pq, 0);

    }

    pq->elements[elem].posn = pq->freelist;

    pq->freelist = elem;

#ifndef NDEBUG

    pq->elements[elem].used = 0;

#endif

    return res;

}

void *ossl_pqueue_remove(OSSL_PQUEUE *pq, size_t elem)

{

    size_t n;

    if (pq == NULL || elem >= pq->hmax || pq->htop == 0)

        return 0;

    ASSERT_ELEM_USED(pq, elem);

    n = pq->elements[elem].posn;

    ASSERT_USED(pq, n);

    if (n == pq->htop - 1) {

        pq->elements[elem].posn = pq->freelist;

        pq->freelist = elem;

#ifndef NDEBUG

        pq->elements[elem].used = 0;

#endif

        return pq->heap[--pq->htop].data;

    }

    if (n > 0)

        pqueue_force_bottom(pq, n);

    return ossl_pqueue_pop(pq);

}

static void pqueue_add_freelist(OSSL_PQUEUE *pq, size_t from)

{

    struct pq_elem_st *e = pq->elements;

    size_t i;

#ifndef NDEBUG

    for (i = from; i < pq->hmax; i++)

        e[i].used = 0;

#endif

    e[from].posn = pq->freelist;

    for (i = from + 1; i < pq->hmax; i++)

        e[i].posn = i - 1;

    pq->freelist = pq->hmax - 1;

}

int ossl_pqueue_reserve(OSSL_PQUEUE *pq, size_t n)

{

    size_t new_max, cur_max;

    struct pq_heap_st *h;

    struct pq_elem_st *e;

    if (pq == NULL)

        return 0;

    cur_max = pq->hmax;

    if (pq->htop + n < cur_max)

        return 1;

    new_max = compute_pqueue_growth(n + cur_max, cur_max);

    if (new_max == 0) {

        ERR_raise(ERR_LIB_SSL, ERR_R_INTERNAL_ERROR);

        return 0;

    }

    h = OPENSSL_realloc(pq->heap, new_max * sizeof(*pq->heap));

    if (h == NULL)

        return 0;

    pq->heap = h;

    e = OPENSSL_realloc(pq->elements, new_max * sizeof(*pq->elements));

    if (e == NULL)

        return 0;

    pq->elements = e;

    pq->hmax = new_max;

    pqueue_add_freelist(pq, cur_max);

    return 1;

}

OSSL_PQUEUE *ossl_pqueue_new(int (*compare)(const void *, const void *))

{

    OSSL_PQUEUE *pq;

    if (compare == NULL)

        return NULL;

    pq = OPENSSL_malloc(sizeof(*pq));

    if (pq == NULL)

        return NULL;

    pq->compare = compare;

    pq->hmax = min_nodes;

    pq->htop = 0;

    pq->freelist = 0;

    pq->heap = OPENSSL_malloc(sizeof(*pq->heap) * min_nodes);

    pq->elements = OPENSSL_malloc(sizeof(*pq->elements) * min_nodes);

    if (pq->heap == NULL || pq->elements == NULL) {

        ossl_pqueue_free(pq);

        return NULL;

    }

    pqueue_add_freelist(pq, 0);

    return pq;

}

void ossl_pqueue_free(OSSL_PQUEUE *pq)

{

    if (pq != NULL) {

        OPENSSL_free(pq->heap);

        OPENSSL_free(pq->elements);

        OPENSSL_free(pq);

    }

}

void ossl_pqueue_pop_free(OSSL_PQUEUE *pq, void (*freefunc)(void *))

{

    size_t i;

    if (pq != NULL) {

        for (i = 0; i < pq->htop; i++)

            (*freefunc)(pq->heap[i].data);

        ossl_pqueue_free(pq);

    }

}

size_t ossl_pqueue_num(const OSSL_PQUEUE *pq)

{

    return pq != NULL ? pq->htop : 0;

}