Function zipStoreEntryEncoding

src/ziplist.c:369–401

Write the encoding header of the entry in 'p'. If p is NULL it just returns * the amount of bytes required to encode such a length. Arguments: * * 'encoding' is the encoding we are using for the entry. It could be * ZIP_INT_* or ZIP_STR_* or between ZIP_INT_IMM_MIN and ZIP_INT_IMM_MAX * for single-byte small immediate integers. * * 'rawlen' is only used for ZIP_STR_* encodings and is the le

 * The function returns the number of bytes used by the encoding/length
 * header stored in 'p'. */
unsigned int zipStoreEntryEncoding(unsigned char *p, unsigned char encoding, unsigned int rawlen) {
    unsigned char len = 1, buf[5];

    if (ZIP_IS_STR(encoding)) {
        /* Although encoding is given it may not be set for strings,
         * so we determine it here using the raw length. */
        if (rawlen <= 0x3f) {
            if (!p) return len;
            buf[0] = ZIP_STR_06B | rawlen;
        } else if (rawlen <= 0x3fff) {
            len += 1;
            if (!p) return len;
            buf[0] = ZIP_STR_14B | ((rawlen >> 8) & 0x3f);
            buf[1] = rawlen & 0xff;
        } else {
            len += 4;
            if (!p) return len;
            buf[0] = ZIP_STR_32B;
            buf[1] = (rawlen >> 24) & 0xff;
            buf[2] = (rawlen >> 16) & 0xff;
            buf[3] = (rawlen >> 8) & 0xff;
            buf[4] = rawlen & 0xff;
        }
    } else {
        /* Implies integer encoding, so length is always 1. */
        if (!p) return len;
        buf[0] = encoding;
    }

    /* Store this length at p. */
    memcpy(p,buf,len);
    return len;
}

/* Decode the entry encoding type and data length (string length for strings,
 * number of bytes used for the integer for integer entries) encoded in 'ptr'.