Function rdbSaveDoubleValue

app/redis-6.2.6/src/rdb.c:578–610

Save a double value. Doubles are saved as strings prefixed by an unsigned * 8 bit integer specifying the length of the representation. * This 8 bit integer has special values in order to specify the following * conditions: * 253: not a number * 254: + inf * 255: - inf */

 * 255: - inf
 */
int rdbSaveDoubleValue(rio *rdb, double val) {
    unsigned char buf[128];
    int len;

    if (isnan(val)) {
        buf[0] = 253;
        len = 1;
    } else if (!isfinite(val)) {
        len = 1;
        buf[0] = (val < 0) ? 255 : 254;
    } else {
#if (DBL_MANT_DIG >= 52) && (LLONG_MAX == 0x7fffffffffffffffLL)
        /* Check if the float is in a safe range to be casted into a
         * long long. We are assuming that long long is 64 bit here.
         * Also we are assuming that there are no implementations around where
         * double has precision < 52 bit.
         *
         * Under this assumptions we test if a double is inside an interval
         * where casting to long long is safe. Then using two castings we
         * make sure the decimal part is zero. If all this is true we use
         * integer printing function that is much faster. */
        double min = -4503599627370495; /* (2^52)-1 */
        double max = 4503599627370496; /* -(2^52) */
        if (val > min && val < max && val == ((double)((long long)val)))
            ll2string((char*)buf+1,sizeof(buf)-1,(long long)val);
        else
#endif
            snprintf((char*)buf+1,sizeof(buf)-1,"%.17g",val);
        buf[0] = strlen((char*)buf+1);
        len = buf[0]+1;
    }
    return rdbWriteRaw(rdb,buf,len);
}

/* For information about double serialization check rdbSaveDoubleValue() */
int rdbLoadDoubleValue(rio *rdb, double *val) {