varint.c

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/*****************************************************************************
 *   (c) 2020 Ledger SAS.
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *****************************************************************************/
 
#include <stdint.h>   // uint*_t
#include <stddef.h>   // size_t
#include <stdbool.h>  // bool
 
#include "varint.h"
#include "write.h"
#include "read.h"
 
uint8_t varint_size(uint64_t value)
{
    if (value <= 0xFC) {
        return 1;
    }
 
    if (value <= UINT16_MAX) {
        return 3;
    }
 
    if (value <= UINT32_MAX) {
        return 5;
    }
 
    return 9;  // <= UINT64_MAX
}
 
int varint_read(const uint8_t *in, size_t in_len, uint64_t *value)
{
    if (in_len < 1) {
        return -1;
    }
 
    uint8_t prefix = in[0];
 
    if (prefix == 0xFD) {
        if (in_len < 3) {
            return -1;
        }
        *value = (uint64_t) read_u16_le(in, 1);
        return 3;
    }
 
    if (prefix == 0xFE) {
        if (in_len < 5) {
            return -1;
        }
        *value = (uint64_t) read_u32_le(in, 1);
        return 5;
    }
 
    if (prefix == 0xFF) {
        if (in_len < 9) {
            return -1;
        }
        *value = (uint64_t) read_u64_le(in, 1);
        return 9;
    }
 
    *value = (uint64_t) prefix;  // prefix <= 0xFC
 
    return 1;
}
 
int varint_write(uint8_t *out, size_t offset, uint64_t value)
{
    uint8_t varint_len = varint_size(value);
 
    switch (varint_len) {
        case 1:
            out[offset] = (uint8_t) value;
            break;
        case 3:
            out[offset++] = 0xFD;
            write_u16_le(out, offset, (uint16_t) value);
            break;
        case 5:
            out[offset++] = 0xFE;
            write_u32_le(out, offset, (uint32_t) value);
            break;
        case 9:
            out[offset++] = 0xFF;
            write_u64_le(out, offset, (uint64_t) value);
            break;
        default:
            return -1;
    }
 
    return varint_len;
}