/*
 * 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 <nw/leb128.h>
#include <nw/log.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>

/* The functions below are (somewhat heavily) modified versions of those
 * 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/
 */

static int read_LEB(FILE *const f, const unsigned maxbits,
    const bool sign, unsigned long long *const out)
{
    unsigned long long result = 0;
    unsigned shift = 0, bcnt = 0;
    uint8_t byte;

    for (;;)
    {
        if (!fread(&byte, sizeof byte, 1, f))
            return -1;

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

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

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

    *out = result;
    return 0;
}

int leb128_read_unsigned(FILE *const f, const unsigned maxbits,
    unsigned long long *const out)
{
    return read_LEB(f, maxbits, false, out);
}

int leb128_read_signed(FILE *const f, const unsigned maxbits,
    long long *const out)
{
    unsigned long long value;
    const int ret = read_LEB(f, maxbits, true, &value);

    *out = value;
    return ret;
}