/*
 * nanowasm, a tiny WebAssembly/Wasm interpreter
 * Copyright (C) 2023-2025  Xavier Del Campo Romero
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at https://mozilla.org/MPL/2.0/.
 */


/* The functions below is a (somewhat heavily) modified version of that
 * provided by the wac project: https://github.com/kanaka/wac
 *
 * Copyright (C) Joel Martin <github@martintribe.org>
 * The wac project is licensed under the MPL 2.0 (Mozilla Public License
 * 2.0). The text of the MPL 2.0 license is included below and can be
 * found at https://www.mozilla.org/MPL/2.0/
 */

#include <nanowasm/types.h>
#include <nw/io.h>
#include <nw/log.h>

enum nw_state nwp_leb128(const struct nw_io_cfg *const cfg,
    struct nw_sm_leb128 *const l, const unsigned maxbits, const int sign,
    void *const user)
{
    unsigned char byte;

    for (;;)
    {
        const int n = cfg->read(&byte, sizeof byte, user);
        unsigned long v;

        if (n < 0)
            return NW_FATAL;
        else if (!n)
            return NW_AGAIN;

        v = (unsigned long)(byte & 0x7f) << l->shift;;

        if (l->shift < 32)
            l->result.low |= v;
        else
            l->result.hi |= v;

        l->shift += 7;

        if (!(byte & 0x80))
            break;
        else if (++l->bcnt > (maxbits + 7u - 1u) / 7u)
        {
#ifdef NW_LOG
            long offset;
            const enum nw_state n = cfg->tell(&offset, cfg->user);

            if (n)
                return n;

            nwp_log("leb128 overflow, offset=%#lx\n", (unsigned long)offset);
#endif
            return NW_FATAL;
        }
    }

    if (sign && (l->shift < maxbits) && (byte & 0x40))
    {
        if (l->shift < 32)
            l->result.low |= -1l << (l->shift);
        else
            l->result.hi |= -1l << (l->shift);
    }

    return NW_OK;
}