Function parse_number

crawl-ref/source/json.cc:986–1029

* The JSON spec says that a number shall follow this precise pattern * (spaces and quotes added for readability): * '-'? (0 | [1-9][0-9]*) ('.' [0-9]+)? ([Ee] [+-]? [0-9]+)? * * However, some JSON parsers are more liberal. For instance, PHP accepts * '.5' and '1.'. JSON.parse accepts '+3'. * * This function takes the strict approach. */

 * This function takes the strict approach.
 */
bool parse_number(const char **sp, double *out)
{
    const char *s = *sp;

    /* '-'? */
    if (*s == '-')
        s++;

    /* (0 | [1-9][0-9]*) */
    if (*s == '0')
        s++;
    else
    {
        if (!is_digit(*s))
            return false;
        do { s++; } while (is_digit(*s));
    }

    /* ('.' [0-9]+)? */
    if (*s == '.')
    {
        s++;
        if (!is_digit(*s))
            return false;
        do { s++; } while (is_digit(*s));
    }

    /* ([Ee] [+-]? [0-9]+)? */
    if (*s == 'E' || *s == 'e')
    {
        s++;
        if (*s == '+' || *s == '-')
            s++;
        if (!is_digit(*s))
            return false;
        do { s++; } while (is_digit(*s));
    }

    if (out)
        *out = strtod(*sp, nullptr);

    *sp = s;
    return true;
}

static void skip_space(const char **sp)
{