C source code for MSB encoding and decoding

For a detailed explanation see Efficiently encoding variable-length integers in C/C++.

#include <stdint.h>
#include <string.h>

// Little endian encoding
size_t encodeMSBlittleEndian(uint64_t value, uint8_t* out) {
    uint8_t *p = out;
    while (value > 127) {
        *p++ = value | 0x80;
        value >>= 7;
    }
    *p++ = value;
    return p - out;
}

// Little endian decoding
size_t decodeMSBlittleEndian(uint64_t *value, uint8_t* in) {
    // locate end of int
    uint8_t *p = in;
    while (*p++ & 0x80);
    size_t size = p - in;
    //decode int
    uint64_t ret = 0;
    do {
      ret = (ret << 7) | (*--p & 0x7F);
    } while (p != in);
    *value = ret;
    return size;
}

Note that little endian encoding makes encoding fast but requires more work to decode. When encoding the integer once and decoding it many times, big endian encoding should be favored.

// Big endian encoding
size_t encodeMSBbigEndian(uint64_t value, uint8_t* out) {
    uint8_t buf[9], *p = buf + 9;
    *--p = value & 0x7F;
    while (value >>= 7) {
      *--p = value | 0x80;
    }
    size_t size = buf + 9 - p;
    memcpy(out, p, size);
    return size;
}

// Big endian decoding
size_t decodeMSBbigEndian(uint64_t *value, uint8_t* in) {
    uint8_t *p = in;
    uint64_t ret = *p & 0x7F;
    while (*p & 0x80) {
        ret = (ret << 7) | (*++p & 0x7F);
    }
    *value = ret;
    return p - in + 1;
}