src/io/leb128.c


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/*
 * nanowasm, a tiny WebAssembly/Wasm interpreter
 * Copyright (C) 2023-2024  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/.
 */

#include <nanowasm/types.h>
#include <nanowasm/leb128.h>
#include <nw/io.h>
#include <nw/log.h>
#include <stdbool.h>
#include <stdint.h>

enum nw_state nwp_leb128(const struct nw_io_cfg *const cfg,
    struct nw_sm_leb128 *const l, const unsigned maxbits, const bool sign)
{
    uint8_t byte;

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

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

        l->result |= (unsigned long long)(byte & 0x7f) << l->shift;
        l->shift += 7;

        if (!(byte & 0x80))
            break;
        else if (++l->bcnt > (maxbits + 7u - 1u) / 7u)
        {
            LOG("%s: overflow\n", __func__);
            return NW_FATAL;
        }
    }

    if (sign && (l->shift < maxbits) && (byte & 0x40))
        l->result |= -1ll << l->shift;

    return NW_OK;
}