base 128 varint编码解码算法

varint.c

#include <stdio.h>
#include <stdint.h>

int encode_varint(char *buf, uint64_t x)
{
    int n;

    n = 0;

    while (x > 127) {
        buf[n++] = (char) (0x80 | (x & 0x7F));
        x >>= 7;
    }

    buf[n++] = (char) x;
    return n;
}

uint64_t decode_varint(char *buf)
{
    int      shift, n;
    uint64_t x, c;

    n = 0;
    x = 0;

    for (shift = 0; shift < 64; shift += 7) {
        c = (uint64_t) buf[n++];
        x |= (c & 0x7F) << shift;
        if ((c & 0x80) == 0) {
            break;
        }
    }

    return x;
}

/* test */
int main()
{
    char     buf[64];
    int      n;
    uint64_t x;

    n = encode_varint(buf, 1300);
    printf("%d\n", n);

    x = decode_varint(buf);
    printf("%d\n", (int) (x));

    return 0;
}