/*

 * Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.

 * Copyright (c) 2019, Oracle and/or its affiliates.  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/bn.h>

#include "crypto/sparse_array.h"

/*

 * How many bits are used to index each level in the tree structure?

 * This setting determines the number of pointers stored in each node of the

 * tree used to represent the sparse array.  Having more pointers reduces the

 * depth of the tree but potentially wastes more memory.  That is, this is a

 * direct space versus time tradeoff.

 *

 * The large memory model uses twelve bits which means that the are 4096

 * pointers in each tree node.  This is more than sufficient to hold the

 * largest defined NID (as of Feb 2019).  This means that using a NID to

 * index a sparse array becomes a constant time single array look up.

 *

 * The small memory model uses four bits which means the tree nodes contain

 * sixteen pointers.  This reduces the amount of unused space significantly

 * at a cost in time.

 *

 * The library builder is also permitted to define other sizes in the closed

 * interval [2, sizeof(ossl_uintmax_t) * 8].

 */

#ifndef OPENSSL_SA_BLOCK_BITS

# ifdef OPENSSL_SMALL_FOOTPRINT

#  define OPENSSL_SA_BLOCK_BITS           4

# else

#  define OPENSSL_SA_BLOCK_BITS           12

# endif

#elif OPENSSL_SA_BLOCK_BITS < 2 || OPENSSL_SA_BLOCK_BITS > (BN_BITS2 - 1)

# error OPENSSL_SA_BLOCK_BITS is out of range

#endif

/*

 * From the number of bits, work out:

 *    the number of pointers in a tree node;

 *    a bit mask to quickly extract an index and

 *    the maximum depth of the tree structure.

  */

#define SA_BLOCK_MAX            (1 << OPENSSL_SA_BLOCK_BITS)

#define SA_BLOCK_MASK           (SA_BLOCK_MAX - 1)

#define SA_BLOCK_MAX_LEVELS     (((int)sizeof(ossl_uintmax_t) * 8 \

                                  + OPENSSL_SA_BLOCK_BITS - 1) \

                                 / OPENSSL_SA_BLOCK_BITS)

struct sparse_array_st {

    int levels;

    ossl_uintmax_t top;

    size_t nelem;

    void **nodes;

};

OPENSSL_SA *OPENSSL_SA_new(void)

{

    OPENSSL_SA *res = OPENSSL_zalloc(sizeof(*res));

    return res;

}

static void sa_doall(const OPENSSL_SA *sa, void (*node)(void **),

                     void (*leaf)(ossl_uintmax_t, void *, void *), void *arg)

{

    int i[SA_BLOCK_MAX_LEVELS];

    void *nodes[SA_BLOCK_MAX_LEVELS];

    ossl_uintmax_t idx = 0;

    int l = 0;

    i[0] = 0;

    nodes[0] = sa->nodes;

    while (l >= 0) {

        const int n = i[l];

        void ** const p = nodes[l];

        if (n >= SA_BLOCK_MAX) {

            if (p != NULL && node != NULL)

                (*node)(p);

            l--;

            idx >>= OPENSSL_SA_BLOCK_BITS;

        } else {

            i[l] = n + 1;

            if (p != NULL && p[n] != NULL) {

                idx = (idx & ~SA_BLOCK_MASK) | n;

                if (l < sa->levels - 1) {

                    i[++l] = 0;

                    nodes[l] = p[n];

                    idx <<= OPENSSL_SA_BLOCK_BITS;

                } else if (leaf != NULL) {

                    (*leaf)(idx, p[n], arg);

                }

            }

        }

    }

}

static void sa_free_node(void **p)

{

    OPENSSL_free(p);

}

static void sa_free_leaf(ossl_uintmax_t n, void *p, void *arg)

{

    OPENSSL_free(p);

}

void OPENSSL_SA_free(OPENSSL_SA *sa)

{

    sa_doall(sa, &sa_free_node, NULL, NULL);

    OPENSSL_free(sa);

}

void OPENSSL_SA_free_leaves(OPENSSL_SA *sa)

{

    sa_doall(sa, &sa_free_node, &sa_free_leaf, NULL);

    OPENSSL_free(sa);

}

/* Wrap this in a structure to avoid compiler warnings */

struct trampoline_st {

    void (*func)(ossl_uintmax_t, void *);

};

static void trampoline(ossl_uintmax_t n, void *l, void *arg)

{

    ((const struct trampoline_st *)arg)->func(n, l);

}

void OPENSSL_SA_doall(const OPENSSL_SA *sa, void (*leaf)(ossl_uintmax_t,

                                                         void *))

{

    struct trampoline_st tramp;

    tramp.func = leaf;

    if (sa != NULL)

        sa_doall(sa, NULL, &trampoline, &tramp);

}

void OPENSSL_SA_doall_arg(const OPENSSL_SA *sa,

                          void (*leaf)(ossl_uintmax_t, void *, void *),

                          void *arg)

{

    if (sa != NULL)

        sa_doall(sa, NULL, leaf, arg);

}

size_t OPENSSL_SA_num(const OPENSSL_SA *sa)

{

    return sa == NULL ? 0 : sa->nelem;

}

void *OPENSSL_SA_get(const OPENSSL_SA *sa, ossl_uintmax_t n)

{

    int level;

    void **p, *r = NULL;

    if (sa == NULL)

        return NULL;

    if (n <= sa->top) {

        p = sa->nodes;

        for (level = sa->levels - 1; p != NULL && level > 0; level--)

            p = (void **)p[(n >> (OPENSSL_SA_BLOCK_BITS * level))

                           & SA_BLOCK_MASK];

        r = p == NULL ? NULL : p[n & SA_BLOCK_MASK];

    }

    return r;

}

static ossl_inline void **alloc_node(void)

{

    return OPENSSL_zalloc(SA_BLOCK_MAX * sizeof(void *));

}

int OPENSSL_SA_set(OPENSSL_SA *sa, ossl_uintmax_t posn, void *val)

{

    int i, level = 1;

    ossl_uintmax_t n = posn;

    void **p;

    if (sa == NULL)

        return 0;

    for (level = 1; level < SA_BLOCK_MAX_LEVELS; level++)

        if ((n >>= OPENSSL_SA_BLOCK_BITS) == 0)

            break;

    for (;sa->levels < level; sa->levels++) {

        p = alloc_node();

        if (p == NULL)

            return 0;

        p[0] = sa->nodes;

        sa->nodes = p;

    }

    if (sa->top < posn)

        sa->top = posn;

    p = sa->nodes;

    for (level = sa->levels - 1; level > 0; level--) {

        i = (posn >> (OPENSSL_SA_BLOCK_BITS * level)) & SA_BLOCK_MASK;

        if (p[i] == NULL && (p[i] = alloc_node()) == NULL)

            return 0;

        p = p[i];

    }

    p += posn & SA_BLOCK_MASK;

    if (val == NULL && *p != NULL)

        sa->nelem--;

    else if (val != NULL && *p == NULL)

        sa->nelem++;

    *p = val;

    return 1;

}