/****************************************************************************
 * RRDtool 1.8.0 Copyright by Tobi Oetiker, 1997-2022
 ****************************************************************************
 * rrd_rpncalc.c  RPN calculator functions
 ****************************************************************************/

#include <limits.h>
#include <locale.h>
#include <stdlib.h>
#include "rrd_tool.h"
#include <time.h>

#ifdef HAVE_LANGINFO_H
#include <langinfo.h>
#endif
#ifdef _WIN32
#include <windows.h>    /* for GetLocaleInfoEx */
#endif
#include "rrd_strtod.h"
#include "rrd_tool.h"
#include "rrd_rpncalc.h"
// #include "rrd_graph.h"

/* #define DEBUG */

static short addop2str(
    enum op_en op,
    enum op_en op_type,
    char *op_str,
    char **result_str,
    unsigned short *offset);
static int tzoffset(
    time_t);            /* used to implement LTIME */

short rpn_compact(
    rpnp_t *rpnp,
    rpn_cdefds_t **rpnc,
    short *count)
{
    short     i;

    *count = 0;
    /* count the number of rpn nodes */
    while (rpnp[*count].op != OP_END)
        (*count)++;
    if (++(*count) > DS_CDEF_MAX_RPN_NODES) {
        rrd_set_error
            ("Maximum %d RPN nodes permitted. Got %d RPN nodes at present.",
             DS_CDEF_MAX_RPN_NODES - 1, (*count) - 1);
        return -1;
    }

    /* allocate memory */
    *rpnc = (rpn_cdefds_t *) calloc(*count, sizeof(rpn_cdefds_t));
    for (i = 0; rpnp[i].op != OP_END; i++) {
        (*rpnc)[i].op = (char) rpnp[i].op;
        if (rpnp[i].op == OP_NUMBER) {
            /* rpnp.val is a double, rpnc.val is a short */
            double    temp = floor(rpnp[i].val);

            if (temp < SHRT_MIN || temp > SHRT_MAX || temp != rpnp[i].val) {
                rrd_set_error
                    ("constants must be integers in the interval (%d, %d)",
                     SHRT_MIN, SHRT_MAX);
                free(*rpnc);
                return -1;
            }
            (*rpnc)[i].val = (short) temp;
        } else if (rpnp[i].op == OP_VARIABLE || rpnp[i].op == OP_PREV_OTHER) {
            (*rpnc)[i].val = (short) rpnp[i].ptr;
        }
    }
    /* terminate the sequence */
    (*rpnc)[(*count) - 1].op = OP_END;
    return 0;
}

rpnp_t   *rpn_expand(
    rpn_cdefds_t *rpnc)
{
    short     i;
    rpnp_t   *rpnp;

    /* DS_CDEF_MAX_RPN_NODES is small, so at the expense of some wasted
     * memory we avoid any reallocs */
    rpnp = (rpnp_t *) calloc(DS_CDEF_MAX_RPN_NODES, sizeof(rpnp_t));
    if (rpnp == NULL) {
        rrd_set_error("failed allocating rpnp array");
        return NULL;
    }
    for (i = 0; rpnc[i].op != OP_END; ++i) {
        rpnp[i].op = (enum op_en) rpnc[i].op;
        rpnp[i].extra = NULL;
        rpnp[i].free_extra = NULL;
        if (rpnp[i].op == OP_NUMBER) {
            rpnp[i].val = (double) rpnc[i].val;
        } else if (rpnp[i].op == OP_VARIABLE || rpnp[i].op == OP_PREV_OTHER) {
            rpnp[i].ptr = (long) rpnc[i].val;
        }
    }
    /* terminate the sequence */
    rpnp[i].op = OP_END;
    return rpnp;
}

/* rpn_compact2str: convert a compact sequence of RPN operator nodes back
 * into a CDEF string. This function is used by rrd_dump.
 * arguments:
 *  rpnc: an array of compact RPN operator nodes
 *  ds_def: a pointer to the data source definition section of an RRD header
 *   for lookup of data source names by index
 *  str: out string, memory is allocated by the function, must be freed by the
 *   the caller */
void rpn_compact2str(
    rpn_cdefds_t *rpnc,
    ds_def_t *ds_def,
    char **str)
{
    unsigned short i, offset = 0;
    char      buffer[7];    /* short as a string */

    for (i = 0; rpnc[i].op != OP_END; i++) {
        if (i > 0)
            (*str)[offset++] = ',';

#define add_op(VV,VVV) \
	  if (addop2str((enum op_en)(rpnc[i].op), VV, VVV, str, &offset) == 1) continue;

        if (rpnc[i].op == OP_NUMBER) {
            /* convert a short into a string */
#if defined(_WIN32) && !defined(__CYGWIN__) && !defined(__CYGWIN32__)
            _itoa(rpnc[i].val, buffer, 10);
#else
            snprintf(buffer, sizeof buffer, "%d", rpnc[i].val);
#endif
            add_op(OP_NUMBER, buffer)
        }

        if (rpnc[i].op == OP_VARIABLE) {
            char     *ds_name = ds_def[rpnc[i].val].ds_nam;

            add_op(OP_VARIABLE, ds_name)
        }

        if (rpnc[i].op == OP_PREV_OTHER) {
            char     *ds_name = ds_def[rpnc[i].val].ds_nam;

            add_op(OP_VARIABLE, ds_name)
        }
#undef add_op

#define add_op(VV,VVV) \
	  if (addop2str((enum op_en)rpnc[i].op, VV, #VVV, str, &offset) == 1) continue;

        add_op(OP_ADD, +)
            add_op(OP_SUB, -)
            add_op(OP_MUL, *)
            add_op(OP_DIV, /)
            add_op(OP_MOD, %)
            add_op(OP_SIN, SIN)
            add_op(OP_COS, COS)
            add_op(OP_LOG, LOG)
            add_op(OP_FLOOR, FLOOR)
            add_op(OP_CEIL, CEIL)
            add_op(OP_EXP, EXP)
            add_op(OP_DUP, DUP)
            add_op(OP_EXC, EXC)
            add_op(OP_POP, POP)
            add_op(OP_LT, LT)
            add_op(OP_LE, LE)
            add_op(OP_GT, GT)
            add_op(OP_GE, GE)
            add_op(OP_EQ, EQ)
            add_op(OP_IF, IF)
            add_op(OP_MIN, MIN)
            add_op(OP_MAX, MAX)
            add_op(OP_LIMIT, LIMIT)
            add_op(OP_UNKN, UNKN)
            add_op(OP_UN, UN)
            add_op(OP_NEGINF, NEGINF)
            add_op(OP_NE, NE)
            add_op(OP_PREV, PREV)
            add_op(OP_INF, INF)
            add_op(OP_ISINF, ISINF)
            add_op(OP_NOW, NOW)
            add_op(OP_LTIME, LTIME)
            add_op(OP_NEWDAY, NEWDAY)
            add_op(OP_NEWWEEK, NEWWEEK)
            add_op(OP_NEWMONTH, NEWMONTH)
            add_op(OP_NEWYEAR, NEWYEAR)
            add_op(OP_STEPWIDTH, STEPWIDTH)
            add_op(OP_TIME, TIME)
            add_op(OP_ATAN2, ATAN2)
            add_op(OP_ATAN, ATAN)
            add_op(OP_SQRT, SQRT)
            add_op(OP_SORT, SORT)
            add_op(OP_COUNT, COUNT)
            add_op(OP_REV, REV)
            add_op(OP_TREND, TREND)
            add_op(OP_TRENDNAN, TRENDNAN)
            add_op(OP_PREDICT, PREDICT)
            add_op(OP_PREDICTSIGMA, PREDICTSIGMA)
            add_op(OP_PREDICTPERC, PREDICTPERC)
            add_op(OP_RAD2DEG, RAD2DEG)
            add_op(OP_DEG2RAD, DEG2RAD)
            add_op(OP_AVG, AVG)
            add_op(OP_ABS, ABS)
            add_op(OP_ADDNAN, ADDNAN)
            add_op(OP_MINNAN, MINNAN)
            add_op(OP_MAXNAN, MAXNAN)
            add_op(OP_MEDIAN, MEDIAN)
            add_op(OP_PERCENT, PERCENT)
            add_op(OP_SMAX, SMAX)
            add_op(OP_SMIN, SMIN)
            add_op(OP_STDEV, STDEV)
            add_op(OP_DEPTH, DEPTH)
            add_op(OP_COPY, COPY)
            add_op(OP_ROLL, ROLL)
            add_op(OP_INDEX, INDEX)
            add_op(OP_POW, POW)
            add_op(OP_ROUND, ROUND)
#undef add_op
    }
    (*str)[offset] = '\0';

}

static short addop2str(
    enum op_en op,
    enum op_en op_type,
    char *op_str,
    char **result_str,
    unsigned short *offset)
{
    if (op == op_type) {
        short     op_len;

        op_len = strlen(op_str);
        *result_str = (char *) rrd_realloc(*result_str,
                                           (op_len + 1 +
                                            *offset) * sizeof(char));
        if (*result_str == NULL) {
            rrd_set_error("failed to alloc memory in addop2str");
            return -1;
        }
        strncpy(*result_str + *offset, op_str, op_len + 1);
        *offset += op_len;
        return 1;
    }
    return 0;
}

void parseCDEF_DS(
    const char *def,
    ds_def_t *ds_def,
    void *key_hash,
    long      (*lookup)(void *,
                        char *)
    )
{
    rpnp_t   *rpnp = NULL;
    rpn_cdefds_t *rpnc = NULL;
    short     count, i;

    rpnp = rpn_parse(key_hash, def, lookup);
    if (rpnp == NULL) {
        rrd_set_error("failed to parse computed data source");
        return;
    }
    /* Check for OP nodes not permitted in COMPUTE DS.
     * Moved this check from within rpn_compact() because it really is
     * COMPUTE DS specific. This is less efficient, but creation doesn't
     * occur too often. */
    for (i = 0; rpnp[i].op != OP_END; i++) {
        if (rpnp[i].op == OP_TIME || rpnp[i].op == OP_LTIME ||
            rpnp[i].op == OP_PREV || rpnp[i].op == OP_COUNT ||
            rpnp[i].op == OP_TREND || rpnp[i].op == OP_TRENDNAN ||
            rpnp[i].op == OP_PREDICT || rpnp[i].op == OP_PREDICTSIGMA ||
            rpnp[i].op == OP_PREDICTPERC ||
            /* these could actually go into COMPUTE with RRD format 06 ... since adding new
               stuff into COMPUTE requires a fileformat update and that can only happen with the
               1.6 release */
            rpnp[i].op == OP_STEPWIDTH ||
            rpnp[i].op == OP_NEWDAY ||
            rpnp[i].op == OP_NEWWEEK ||
            rpnp[i].op == OP_NEWMONTH || rpnp[i].op == OP_NEWYEAR) {

            rrd_set_error
                ("operators TIME LTIME STEPWIDTH PREV NEW* COUNT TREND TRENDNAN PREDICT PREDICTSIGMA PREDICTPERC are not supported with DS COMPUTE");
            free(rpnp);
            return;
        }
    }
    if (rpn_compact(rpnp, &rpnc, &count) == -1) {
        free(rpnp);
        return;
    }
    /* copy the compact rpn representation over the ds_def par array */
    memcpy((void *) &(ds_def->par[DS_cdef]),
           (void *) rpnc, count * sizeof(rpn_cdefds_t));
    free(rpnp);
    free(rpnc);
}

/* lookup a data source name in the rrd struct and return the index,
 * should use ds_match() here except:
 * (1) need a void * pointer to the rrd
 * (2) error handling is left to the caller
 */
long lookup_DS(
    void *rrd_vptr,
    char *ds_name)
{
    unsigned int i;
    rrd_t    *rrd;

    rrd = (rrd_t *) rrd_vptr;

    for (i = 0; i < rrd->stat_head->ds_cnt; ++i) {
        if (strcmp(ds_name, rrd->ds_def[i].ds_nam) == 0)
            return i;
    }
    /* the caller handles a bad data source name in the rpn string */
    return -1;
}

/* rpn_parse : parse a string and generate a rpnp array; modified
 * str2rpn() originally included in rrd_graph.c
 * arguments:
 * key_hash: a transparent argument passed to lookup(); conceptually this
 *    is a hash object for lookup of a numeric key given a variable name
 * expr: the string RPN expression, including variable names
 * lookup(): a function that retrieves a numeric key given a variable name
 */
rpnp_t   *rpn_parse(
    void *key_hash,
    const char *const expr_const,
    long      (*lookup)(void *,
                        char *))
{
    int       pos = 0;
    char     *expr;
    long      steps = -1;
    rpnp_t   *rpnp;
    char      vname[MAX_VNAME_LEN + 10];
    char      double_str[41] = { 0 };

    rpnp = NULL;
    expr = (char *) expr_const;
    if (!*expr) {
        rrd_set_error("can not parse an empty rpn expression");
        return NULL;
    }
    while (*expr) {
        if ((rpnp = (rpnp_t *) rrd_realloc(rpnp, (++steps + 2) *
                                           sizeof(rpnp_t))) == NULL) {
            return NULL;
        }

        else if ((sscanf(expr, "%40[0-9.e+-]%n", double_str, &pos) == 1)
                 && (expr[pos] == ',')
                 && (rrd_strtodbl(double_str, NULL, &(rpnp[steps].val), NULL)
                     == 2)) {
            rpnp[steps].op = OP_NUMBER;
            expr += pos;
        }
#define match_op(VV,VVV) \
        else if (strncmp(expr, #VVV, strlen(#VVV))==0 && ( expr[strlen(#VVV)] == ',' || expr[strlen(#VVV)] == '\0' )){ \
            rpnp[steps].op = VV; \
            expr+=strlen(#VVV); \
    	}

#define match_op_param(VV,VVV) \
        else if (sscanf(expr, #VVV "(" DEF_NAM_FMT ")",vname) == 1) { \
          int length = 0; \
          if ((length = strlen(#VVV)+strlen(vname)+2, \
              expr[length] == ',' || expr[length] == '\0') ) { \
             rpnp[steps].op = VV; \
             rpnp[steps].ptr = (*lookup)(key_hash,vname); \
             if (rpnp[steps].ptr < 0) { \
                           rrd_set_error("variable '%s' not found",vname);\
			   free(rpnp); \
			   return NULL; \
			 } else expr+=length; \
          } \
        }

        match_op(OP_ADD, +)
            match_op(OP_SUB, -)
            match_op(OP_MUL, *)
            match_op(OP_DIV, /)
            match_op(OP_MOD, %)
            match_op(OP_SIN, SIN)
            match_op(OP_COS, COS)
            match_op(OP_LOG, LOG)
            match_op(OP_FLOOR, FLOOR)
            match_op(OP_CEIL, CEIL)
            match_op(OP_EXP, EXP)
            match_op(OP_DUP, DUP)
            match_op(OP_EXC, EXC)
            match_op(OP_POP, POP)
            match_op(OP_LTIME, LTIME)
            match_op(OP_NEWDAY, NEWDAY)
            match_op(OP_NEWWEEK, NEWWEEK)
            match_op(OP_NEWMONTH, NEWMONTH)
            match_op(OP_NEWYEAR, NEWYEAR)
            match_op(OP_STEPWIDTH, STEPWIDTH)
            match_op(OP_LT, LT)
            match_op(OP_LE, LE)
            match_op(OP_GT, GT)
            match_op(OP_GE, GE)
            match_op(OP_EQ, EQ)
            match_op(OP_IF, IF)
            match_op(OP_MIN, MIN)
            match_op(OP_MAX, MAX)
            match_op(OP_LIMIT, LIMIT)
            /* order is important here ! .. match longest first */
            match_op(OP_UNKN, UNKN)
            match_op(OP_UN, UN)
            match_op(OP_NEGINF, NEGINF)
            match_op(OP_NE, NE)
            match_op(OP_COUNT, COUNT)
            match_op_param(OP_PREV_OTHER, PREV)
            match_op(OP_PREV, PREV)
            match_op(OP_INF, INF)
            match_op(OP_ISINF, ISINF)
            match_op(OP_NOW, NOW)
            match_op(OP_TIME, TIME)
            match_op(OP_ATAN2, ATAN2)
            match_op(OP_ATAN, ATAN)
            match_op(OP_SQRT, SQRT)
            match_op(OP_SORT, SORT)
            match_op(OP_REV, REV)
            match_op(OP_TREND, TREND)
            match_op(OP_TRENDNAN, TRENDNAN)
            match_op(OP_PREDICT, PREDICT)
            match_op(OP_PREDICTSIGMA, PREDICTSIGMA)
            match_op(OP_PREDICTPERC, PREDICTPERC)
            match_op(OP_RAD2DEG, RAD2DEG)
            match_op(OP_DEG2RAD, DEG2RAD)
            match_op(OP_AVG, AVG)
            match_op(OP_ABS, ABS)
            match_op(OP_ADDNAN, ADDNAN)
            match_op(OP_MINNAN, MINNAN)
            match_op(OP_MAXNAN, MAXNAN)
            match_op(OP_MEDIAN, MEDIAN)
            match_op(OP_DEPTH, DEPTH)
            match_op(OP_COPY, COPY)
            match_op(OP_ROLL, ROLL)
            match_op(OP_INDEX, INDEX)
            match_op(OP_SMAX, SMAX)
            match_op(OP_SMIN, SMIN)
            match_op(OP_STDEV, STDEV)
            match_op(OP_PERCENT, PERCENT)
            match_op(OP_POW, POW)
            match_op(OP_ROUND, ROUND)
#undef match_op
            else if ((sscanf(expr, DEF_NAM_FMT "%n", vname, &pos) == 1)
                     && (expr[pos] == '\0' || expr[pos] == ',')
                     && ((rpnp[steps].ptr = (*lookup) (key_hash, vname)) !=
                         -1)) {
            rpnp[steps].op = OP_VARIABLE;
            expr += pos;
        }

        else {
            rrd_set_error("don't understand '%s'", expr);
            free(rpnp);
            return NULL;
        }

        rpnp[steps].extra = NULL;
        rpnp[steps].free_extra = NULL;

        if (*expr == 0)
            break;
        if (*expr == ',')
            expr++;
        else {
            rrd_set_error("garbage in RPN: '%s'", expr);
            free(rpnp);
            return NULL;
        }
    }
    rpnp[steps + 1].op = OP_END;
    return rpnp;
}

void rpnstack_init(
    rpnstack_t *rpnstack)
{
    rpnstack->s = NULL;
    rpnstack->dc_stacksize = 0;
    rpnstack->dc_stackblock = 1000;
}

void rpnstack_free(
    rpnstack_t *rpnstack)
{
    free(rpnstack->s);
    rpnstack->dc_stacksize = 0;
}

void rpnp_freeextra(
    rpnp_t *rpnp)
{
    int       rpi;

    if (!rpnp)
        return;
    /* process each op from the rpn in turn */
    for (rpi = 0; rpnp[rpi].op != OP_END; rpi++) {
        if (rpnp[rpi].extra) {
            if (rpnp[rpi].free_extra) {
                rpnp[rpi].free_extra(rpnp[rpi].extra);
            } else {
                free(rpnp[rpi].extra);
            }
            rpnp[rpi].extra = NULL;
        }
    }
}

static int rpn_compare_double(
    const void *x,
    const void *y)
{
    /* First catch NaN values. They are smallest */
    if (isnan(*(double *) x) && isnan(*(double *) y))
        return 0;
    if (isnan(*(double *) x))
        return -1;
    if (isnan(*(double *) y))
        return 1;
    /* NaN doesn't reach this part so INF and -INF are extremes.
     * The sign from isinf() is compatible with the sign we return
     */
    if (isinf(*(double *) x))
        return isinf(*(double *) x);
    if (isinf(*(double *) y))
        return isinf(*(double *) y);

    double    diff = *((const double *) x) - *((const double *) y);

    return (diff < 0) ? -1 : (diff > 0) ? 1 : 0;
}

int find_first_weekday(
    void)
{
    static int first_weekday = -1;

    if (first_weekday == -1) {
#ifdef HAVE__NL_TIME_WEEK_1STDAY
        /* according to http://sourceware.org/ml/libc-locales/2009-q1/msg00011.html */
        /* See correct way here http://pasky.or.cz/dev/glibc/first_weekday.c */
        first_weekday = nl_langinfo(_NL_TIME_FIRST_WEEKDAY)[0];
        int       week_1stday;
        long      week_1stday_l = (long) nl_langinfo(_NL_TIME_WEEK_1STDAY);

        if (week_1stday_l == 19971130
#if SIZEOF_LONG_INT > 4
            || week_1stday_l >> 32 == 19971130
#endif
            )
            week_1stday = 0;    /* Sun */
        else if (week_1stday_l == 19971201
#if SIZEOF_LONG_INT > 4
                 || week_1stday_l >> 32 == 19971201
#endif
            )
            week_1stday = 1;    /* Mon */
        else {
            first_weekday = 1;
            return first_weekday;   /* we go for a Monday default */
        }
        first_weekday = (week_1stday + first_weekday - 1) % 7;
#elif defined(_WIN32) && defined(LOCALE_NAME_USER_DEFAULT)
        DWORD     week_1stday;

        GetLocaleInfoEx(LOCALE_NAME_USER_DEFAULT,
                        LOCALE_IFIRSTDAYOFWEEK | LOCALE_RETURN_NUMBER,
                        (LPWSTR) & week_1stday,
                        sizeof(week_1stday) / sizeof(WCHAR));
        /* 0:Monday, ..., 6:Sunday. */
        /* We need 1 for Monday, 0 for Sunday. */
        first_weekday = (week_1stday + 1) % 7;
#else
        first_weekday = 0;
#endif
    }
#ifdef DEBUG
    printf("first_weekday = %d\n", first_weekday);
#endif
    return first_weekday;
}

/* rpn_calc: run the RPN calculator; also performs variable substitution;
 * moved and modified from data_calc() originally included in rrd_graph.c
 * arguments:
 * rpnp : an array of RPN operators (including variable references)
 * rpnstack : the initialized stack
 * data_idx : when data_idx is a multiple of rpnp.step, the rpnp.data pointer
 *   is advanced by rpnp.ds_cnt; used only for variable substitution
 * output : an array of output values; OP_PREV assumes this array contains
 *   the "previous" value at index position output_idx-1; the definition of
 *   "previous" depends on the calling environment
 * output_idx : an index into the output array in which to store the output
 *   of the RPN calculator
 * returns: -1 if the computation failed (also calls rrd_set_error)
 *           0 on success
 */
short rpn_calc(
    rpnp_t *rpnp,
    rpnstack_t *rpnstack,
    long data_idx,
    rrd_value_t *output,
    int output_idx,
    int step_width)
{
    int       rpi;
    long      stptr = -1;
    struct tm tmtmp1, tmtmp2;
    time_t    timetmp;

    /* process each op from the rpn in turn */
    for (rpi = 0; rpnp[rpi].op != OP_END; rpi++) {
        /* allocate or grow the stack */
        if (stptr + 5 > rpnstack->dc_stacksize) {
            /* could move this to a separate function */
            rpnstack->dc_stacksize += rpnstack->dc_stackblock;
            rpnstack->s = (double *) rrd_realloc(rpnstack->s,
                                                 (rpnstack->dc_stacksize) *
                                                 sizeof(*(rpnstack->s)));
            if (rpnstack->s == NULL) {
                rrd_set_error("RPN stack overflow");
                return -1;
            }
        }
#define stackunderflow(MINSIZE)				\
	if(stptr<MINSIZE){				\
	    rrd_set_error("RPN stack underflow");	\
	    return -1;					\
	}

        switch (rpnp[rpi].op) {
        case OP_NUMBER:
            rpnstack->s[++stptr] = rpnp[rpi].val;
            break;
        case OP_VARIABLE:
        case OP_PREV_OTHER:
            /* Sanity check: VDEFs shouldn't make it here */
            if (rpnp[rpi].ds_cnt == 0) {
                rrd_set_error("VDEF made it into rpn_calc... aborting");
                return -1;
            } else {
                /* make sure we pull the correct value from
                 * the *.data array. Adjust the pointer into
                 * the array accordingly. Advance the ptr one
                 * row in the rra (skip over non-relevant
                 * data sources)
                 */
                if (rpnp[rpi].op == OP_VARIABLE) {
                    rpnstack->s[++stptr] = *(rpnp[rpi].data);
                } else {
                    if ((output_idx) <= 0) {
                        rpnstack->s[++stptr] = DNAN;
                    } else {
                        rpnstack->s[++stptr] =
                            *(rpnp[rpi].data - rpnp[rpi].ds_cnt);
                    }

                }
                if (data_idx % rpnp[rpi].step == 0) {
                    rpnp[rpi].data += rpnp[rpi].ds_cnt;
                }
            }
            break;
        case OP_STEPWIDTH:
            rpnstack->s[++stptr] = step_width;
            break;
        case OP_COUNT:
            rpnstack->s[++stptr] = (output_idx + 1);    /* Note: Counter starts at 1 */
            break;
        case OP_PREV:
            if ((output_idx) <= 0) {
                rpnstack->s[++stptr] = DNAN;
            } else {
                rpnstack->s[++stptr] = output[output_idx - 1];
            }
            break;
        case OP_UNKN:
            rpnstack->s[++stptr] = DNAN;
            break;
        case OP_INF:
            rpnstack->s[++stptr] = DINF;
            break;
        case OP_NEGINF:
            rpnstack->s[++stptr] = -DINF;
            break;
        case OP_NOW:
            rpnstack->s[++stptr] = (double) time(NULL);
            break;
        case OP_TIME:
            /* HACK: this relies on the data_idx being the time,
             ** which the within-function scope is unaware of */
            rpnstack->s[++stptr] = (double) data_idx;
            break;
        case OP_LTIME:
            rpnstack->s[++stptr] =
                (double) tzoffset(data_idx) + (double) data_idx;
            break;
        case OP_NEWDAY:
            timetmp = data_idx;
            localtime_r(&timetmp, &tmtmp1);
            timetmp = data_idx - step_width;
            localtime_r(&timetmp, &tmtmp2);
            rpnstack->s[++stptr] =
                tmtmp1.tm_mday != tmtmp2.tm_mday ? 1.0 : 0.0;
            break;
        case OP_NEWWEEK:
            timetmp = data_idx;
            localtime_r(&timetmp, &tmtmp1);
            timetmp = data_idx - step_width;
            localtime_r(&timetmp, &tmtmp2);
            rpnstack->s[++stptr] = (tmtmp1.tm_wday == find_first_weekday()
                                    && tmtmp1.tm_wday !=
                                    tmtmp2.tm_wday) ? 1.0 : 0.0;
            break;
        case OP_NEWMONTH:
            timetmp = data_idx;
            localtime_r(&timetmp, &tmtmp1);
            timetmp = data_idx - step_width;
            localtime_r(&timetmp, &tmtmp2);
            rpnstack->s[++stptr] = tmtmp1.tm_mon != tmtmp2.tm_mon ? 1.0 : 0.0;
            break;
        case OP_NEWYEAR:
            timetmp = data_idx;
            localtime_r(&timetmp, &tmtmp1);
            timetmp = data_idx - step_width;
            localtime_r(&timetmp, &tmtmp2);
            rpnstack->s[++stptr] =
                tmtmp1.tm_year != tmtmp2.tm_year ? 1.0 : 0.0;
            break;
        case OP_ADD:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1]
                + rpnstack->s[stptr];
            stptr--;
            break;
        case OP_ADDNAN:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1])) {
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            } else if (isnan(rpnstack->s[stptr])) {
                /* NOOP */
                /* rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1]; */
            } else {
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1]
                    + rpnstack->s[stptr];
            }

            stptr--;
            break;
        case OP_SUB:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1]
                - rpnstack->s[stptr];
            stptr--;
            break;
        case OP_MUL:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = (rpnstack->s[stptr - 1])
                * (rpnstack->s[stptr]);
            stptr--;
            break;
        case OP_DIV:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1]
                / rpnstack->s[stptr];
            stptr--;
            break;
        case OP_MOD:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = fmod(rpnstack->s[stptr - 1]
                                          , rpnstack->s[stptr]);
            stptr--;
            break;
        case OP_POW:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = pow(rpnstack->s[stptr - 1]
                                         , rpnstack->s[stptr]);
            stptr--;
            break;
        case OP_SIN:
            stackunderflow(0);
            rpnstack->s[stptr] = sin(rpnstack->s[stptr]);
            break;
        case OP_ATAN:
            stackunderflow(0);
            rpnstack->s[stptr] = atan(rpnstack->s[stptr]);
            break;
        case OP_RAD2DEG:
            stackunderflow(0);
            rpnstack->s[stptr] = 57.29577951 * rpnstack->s[stptr];
            break;
        case OP_DEG2RAD:
            stackunderflow(0);
            rpnstack->s[stptr] = 0.0174532952 * rpnstack->s[stptr];
            break;
        case OP_ATAN2:
            stackunderflow(1);
            rpnstack->s[stptr - 1] = atan2(rpnstack->s[stptr - 1],
                                           rpnstack->s[stptr]);
            stptr--;
            break;
        case OP_COS:
            stackunderflow(0);
            rpnstack->s[stptr] = cos(rpnstack->s[stptr]);
            break;
        case OP_CEIL:
            stackunderflow(0);
            rpnstack->s[stptr] = ceil(rpnstack->s[stptr]);
            break;
        case OP_ROUND:
            stackunderflow(0);
            rpnstack->s[stptr] = round(rpnstack->s[stptr]);
            break;
        case OP_FLOOR:
            stackunderflow(0);
            rpnstack->s[stptr] = floor(rpnstack->s[stptr]);
            break;
        case OP_LOG:
            stackunderflow(0);
            rpnstack->s[stptr] = log(rpnstack->s[stptr]);
            break;
        case OP_DUP:
            stackunderflow(0);
            rpnstack->s[stptr + 1] = rpnstack->s[stptr];
            stptr++;
            break;
        case OP_POP:
            stackunderflow(0);
            stptr--;
            break;
        case OP_EXC:
            stackunderflow(1);
            {
                double    dummy;

                dummy = rpnstack->s[stptr];
                rpnstack->s[stptr] = rpnstack->s[stptr - 1];
                rpnstack->s[stptr - 1] = dummy;
            }
            break;
        case OP_EXP:
            stackunderflow(0);
            rpnstack->s[stptr] = exp(rpnstack->s[stptr]);
            break;
        case OP_LT:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1] <
                    rpnstack->s[stptr] ? 1.0 : 0.0;
            stptr--;
            break;
        case OP_LE:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1] <=
                    rpnstack->s[stptr] ? 1.0 : 0.0;
            stptr--;
            break;
        case OP_GT:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1] >
                    rpnstack->s[stptr] ? 1.0 : 0.0;
            stptr--;
            break;
        case OP_GE:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1] >=
                    rpnstack->s[stptr] ? 1.0 : 0.0;
            stptr--;
            break;
        case OP_NE:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1] ==
                    rpnstack->s[stptr] ? 0.0 : 1.0;
            stptr--;
            break;
        case OP_EQ:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else
                rpnstack->s[stptr - 1] = rpnstack->s[stptr - 1] ==
                    rpnstack->s[stptr] ? 1.0 : 0.0;
            stptr--;
            break;
        case OP_IF:
            stackunderflow(2);
            rpnstack->s[stptr - 2] = (isnan(rpnstack->s[stptr - 2])
                                      || rpnstack->s[stptr - 2] ==
                                      0.0) ? rpnstack->
                s[stptr] : rpnstack->s[stptr - 1];
            stptr--;
            stptr--;
            break;
        case OP_MIN:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else if (rpnstack->s[stptr - 1] > rpnstack->s[stptr])
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            stptr--;
            break;
        case OP_MINNAN:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else if (isnan(rpnstack->s[stptr]));
            else if (rpnstack->s[stptr - 1] > rpnstack->s[stptr])
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            stptr--;
            break;
        case OP_MAX:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]));
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else if (rpnstack->s[stptr - 1] < rpnstack->s[stptr])
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            stptr--;
            break;
        case OP_MAXNAN:
            stackunderflow(1);
            if (isnan(rpnstack->s[stptr - 1]))
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            else if (isnan(rpnstack->s[stptr]));
            else if (rpnstack->s[stptr - 1] < rpnstack->s[stptr])
                rpnstack->s[stptr - 1] = rpnstack->s[stptr];
            stptr--;
            break;
        case OP_LIMIT:
            stackunderflow(2);
            if (isnan(rpnstack->s[stptr - 2]));
            else if (isnan(rpnstack->s[stptr - 1]))
                rpnstack->s[stptr - 2] = rpnstack->s[stptr - 1];
            else if (isnan(rpnstack->s[stptr]))
                rpnstack->s[stptr - 2] = rpnstack->s[stptr];
            else if (rpnstack->s[stptr - 2] < rpnstack->s[stptr - 1])
                rpnstack->s[stptr - 2] = DNAN;
            else if (rpnstack->s[stptr - 2] > rpnstack->s[stptr])
                rpnstack->s[stptr - 2] = DNAN;
            stptr -= 2;
            break;
        case OP_UN:
            stackunderflow(0);
            rpnstack->s[stptr] = isnan(rpnstack->s[stptr]) ? 1.0 : 0.0;
            break;
        case OP_ISINF:
            stackunderflow(0);
            rpnstack->s[stptr] = isinf(rpnstack->s[stptr]) ? 1.0 : 0.0;
            break;
        case OP_SQRT:
            stackunderflow(0);
            rpnstack->s[stptr] = sqrt(rpnstack->s[stptr]);
            break;
        case OP_SORT:
            stackunderflow(0);
            {
                int       spn = (int) rpnstack->s[stptr--];

                stackunderflow(spn - 1);
                qsort(rpnstack->s + stptr - spn + 1, spn, sizeof(double),
                      rpn_compare_double);
            }
            break;
        case OP_REV:
            stackunderflow(0);
            {
                int       spn = (int) rpnstack->s[stptr--];
                double   *p, *q;

                stackunderflow(spn - 1);

                p = rpnstack->s + stptr - spn + 1;
                q = rpnstack->s + stptr;
                while (p < q) {
                    double    x = *q;

                    *q-- = *p;
                    *p++ = x;
                }
            }
            break;
        case OP_PREDICT:
        case OP_PREDICTSIGMA:
        case OP_PREDICTPERC:
        {
            /* the percentile requested */
            double    percentile = DNAN;

            if (rpnp[rpi].op == OP_PREDICTPERC) {
                stackunderflow(1);
                percentile = rpnstack->s[--stptr];
                if (fabs(percentile) > 100) {
                    rrd_set_error("unsupported percentile: %f", percentile);
                    return -1;
                }
                percentile /= 100;
            }
            /* the local averaging window (similar to trend,
             * but better here, as we get better statistics
             * thru numbers)*/
            stackunderflow(2);
            int       locstepsize = rpnstack->s[--stptr];

            /* the number of shifts and range-checking */
            int       shifts = rpnstack->s[--stptr];

            stackunderflow(shifts);
            // handle negative shifts special
            if (shifts < 0) {
                stptr--;
            } else {
                stptr -= shifts;
            }
            /* the real calculation */
            double    val = DNAN;

            /* the info on the datasource */
            time_t    dsstep = (time_t) rpnp[rpi - 1].step;
            int       dscount = rpnp[rpi - 1].ds_cnt;
            int       locstep =
                (int) ceil((float) locstepsize / (float) dsstep);

            /* the sums */
            double    sum = 0;
            double    sum2 = 0;
            int       count = 0;

            /* now loop for each position */
            int       doshifts = shifts;

            if (shifts < 0) {
                doshifts = -shifts;
            }
            /* alloc memory */
            double   *extra = (double *) rpnp[rpi].extra;

            if (rpnp[rpi].op == OP_PREDICTPERC) {
                if (!extra) {
                    int       size = (doshifts + 1) * (locstep + 2);

                    rpnp[rpi].extra =
                        extra = (double *) malloc(sizeof(double) * size);
                }
            }
            /* loop the shifts */
            for (int loop = 0; loop < doshifts; loop++) {
                /* calculate shift step */
                int       shiftstep = 1;

                if (shifts < 0) {
                    shiftstep = loop * rpnstack->s[stptr];
                } else {
                    shiftstep = rpnstack->s[stptr + loop];
                }
                if (shiftstep < 0) {
                    rrd_set_error("negative shift step not allowed: %i",
                                  shiftstep);
                    return -1;
                }
                shiftstep = (int) ceil((float) shiftstep / (float) dsstep);
                /* loop all local shifts */
                for (int i = 0; i <= locstep; i++) {
                    /* now calculate offset into data-array
                     * - relative to output_idx */
                    int       offset = shiftstep + i;

                    /* and process if we have index 0 of above */
                    if ((offset >= 0) && (offset < output_idx)) {
                        /* get the value */
                        val = rpnp[rpi - 1].data[-dscount * offset];
                        /* and handle the non NAN case only */
                        if (!isnan(val)) {
                            sum += val;
                            sum2 += val * val;
                            if (extra) {
                                extra[count] = val;
                            }
                            count++;
                        }
                    }
                }
            }
            /* do the final calculations */
            val = DNAN;
            switch (rpnp[rpi].op) {
            case OP_PREDICT:
                if (count > 0) {
                    val = sum / (double) count;
                }
                break;
            case OP_PREDICTSIGMA:
                if (count > 1) {    /* the sigma case */
                    val = count * sum2 - sum * sum;
                    if (val < 0) {
                        val = DNAN;
                    } else {
                        val =
                            sqrt(val /
                                 ((float) count * ((float) count - 1.0)));
                    }
                }
                break;
            case OP_PREDICTPERC:
                if ((count > 0) && extra) {
                    /* sort the numbers */
                    qsort(extra, count, sizeof(double), rpn_compare_double);
                    /* get the percentile selected */
                    double    idxf = percentile * ((float) count - 1.0);

                    if (percentile < 0) {   /* take the next best */
                        int       idx = round(fabs(idxf));

                        val = extra[idx];
                    } else {    /* interpolate */
                        int       idx = floor(idxf);
                        double    deltax = idxf - idx;

                        val = extra[idx];
                        if (deltax) {   /* this check also handles the percentile=100 case */
                            double    deltay = extra[idx + 1] - extra[idx];

                            val += deltay * deltax;
                        }
                    }
                }
                break;
            default:   /* should not get here ... */
                break;
            }
            rpnstack->s[stptr] = val;
        }
            break;
        case OP_TREND:
        case OP_TRENDNAN:
            stackunderflow(1);
            if ((rpi < 2) || (rpnp[rpi - 2].op != OP_VARIABLE)) {
                rrd_set_error("malformed trend arguments");
                return -1;
            } else {
                time_t    dur = (time_t) rpnstack->s[stptr];
                time_t    step = (time_t) rpnp[rpi - 2].step;

                if (output_idx + 1 >= (int) ceil((float) dur / (float) step)) {
                    int       ignorenan = (rpnp[rpi].op == OP_TREND);
                    double    accum = 0.0;
                    int       i = -1;   /* pick the current entries, not the next one
                                           as the data pointer has already been forwarded
                                           when the OP_VARIABLE was processed */
                    int       count = 0;

                    do {
                        double    val =
                            rpnp[rpi - 2].data[rpnp[rpi - 2].ds_cnt * i--];
                        if (ignorenan || !isnan(val)) {
                            accum += val;
                            ++count;
                        }

                        dur -= step;
                    } while (dur > 0);

                    rpnstack->s[--stptr] =
                        (count == 0) ? DNAN : (accum / count);
                } else
                    rpnstack->s[--stptr] = DNAN;
            }
            break;
        case OP_AVG:
            stackunderflow(0);
            {
                int       i = (int) rpnstack->s[stptr--];
                double    sum = 0;
                int       count = 0;

                stackunderflow(i - 1);
                while (i > 0) {
                    double    val = rpnstack->s[stptr--];

                    i--;
                    if (isnan(val)) {
                        continue;
                    }
                    count++;
                    sum += val;
                }
                /* now push the result back on stack */
                if (count > 0) {
                    rpnstack->s[++stptr] = sum / count;
                } else {
                    rpnstack->s[++stptr] = DNAN;
                }
            }
            break;
        case OP_ABS:
            stackunderflow(0);
            rpnstack->s[stptr] = fabs(rpnstack->s[stptr]);
            break;
        case OP_MEDIAN:
            stackunderflow(0);
            {
                int       elements = (int) rpnstack->s[stptr--];
                int       final_elements = elements;
                double   *element_ptr = rpnstack->s + stptr - elements + 1;
                double   *goodvals = element_ptr;
                double   *badvals = element_ptr + elements - 1;

                stackunderflow(elements - 1);

                /* move values to consolidate the non-NANs for sorting, keeping
                 * track of how many NANs we encounter. */
                while (goodvals < badvals) {
                    if (isnan(*goodvals)) {
                        *goodvals = *badvals--;
                        --final_elements;
                    } else {
                        ++goodvals;
                    }
                }

                /* when goodvals and badvals meet, they might have met on a
                 * NAN, which wouldn't decrease final_elements. so, check
                 * that now. */
                if (isnan(*goodvals))
                    --final_elements;

                stptr -= elements;
                if (!final_elements) {
                    /* no non-NAN elements; push NAN */
                    rpnstack->s[++stptr] = DNAN;
                } else {
                    /* and finally, take the median of the remaining non-NAN
                     * elements. */
                    qsort(element_ptr, final_elements, sizeof(double),
                          rpn_compare_double);
                    if (final_elements % 2 == 1) {
                        rpnstack->s[++stptr] =
                            element_ptr[final_elements / 2];
                    } else {
                        rpnstack->s[++stptr] =
                            0.5 * (element_ptr[final_elements / 2] +
                                   element_ptr[final_elements / 2 - 1]);
                    }
                }
            }
            break;
        case OP_STDEV:
            stackunderflow(0);
            {
                int       elements = (int) rpnstack->s[stptr--];

                stackunderflow(elements - 1);
                int       n = 0;
                rrd_value_t mean = 0;
                rrd_value_t mean2 = 0;

                while (elements--) {
                    rrd_value_t datum = rpnstack->s[stptr--];
                    rrd_value_t delta;

                    if (isnan(datum)) {
                        continue;
                    }
                    n++;
                    delta = datum - mean;
                    mean += delta / n;
                    mean2 += delta * (datum - mean);
                }
                rpnstack->s[++stptr] = n < 2 ? DNAN : sqrt(mean2 / (n - 1));
            }
            break;
        case OP_PERCENT:
            stackunderflow(2);
            {
                int       elements = (int) rpnstack->s[stptr--];
                double    percent = rpnstack->s[stptr--];

                if (!(percent >= 0 && percent <= 100)) {
                    rrd_set_error
                        ("percentile argument must be between 0 and 100");
                    return -1;
                }

                stackunderflow(elements - 1);
                qsort(rpnstack->s + stptr - elements + 1, elements,
                      sizeof(double), rpn_compare_double);
                stptr -= elements;
                rpnstack->s[stptr + 1] =
                    rpnstack->s[stptr +
                                (int) round(percent * (double) (elements) /
                                            100.0)];
                stptr++;
            }
            break;
        case OP_SMAX:
            stackunderflow(0);
            {
                rrd_value_t ximum = DNAN;
                int       elements = (int) rpnstack->s[stptr--];

                stackunderflow(elements - 1);
                while (elements--) {
                    rrd_value_t element = rpnstack->s[stptr--];

                    if (isnan(ximum) || element > ximum) {
                        ximum = element;
                    }
                }
                rpnstack->s[++stptr] = ximum;
            }
            break;
        case OP_SMIN:
            stackunderflow(0);
            {
                rrd_value_t ximum = DNAN;
                int       elements = (int) rpnstack->s[stptr--];

                stackunderflow(elements - 1);
                while (elements--) {
                    rrd_value_t element = rpnstack->s[stptr--];

                    if (isnan(ximum) || element < ximum) {
                        ximum = element;
                    }
                }
                rpnstack->s[++stptr] = ximum;
            }
            break;
        case OP_ROLL:
            stackunderflow(1);
            {
                int       step = (int) rpnstack->s[stptr--];
                int       base = (int) rpnstack->s[stptr--];
                int       i = base;
                int       j = i + step;
                double   *tmp_stack;

                stackunderflow(base - 1);
                tmp_stack = (double *) malloc(sizeof(double) * base);
                if (!tmp_stack) {
                    rrd_set_error("RPN out of memory (allocating %i objects)",
                                  base);
                    return -1;
                }
                memcpy(tmp_stack, rpnstack->s + stptr,
                       (sizeof(double) * base));
                while (i--) {
                    j--;
                    while (j < 0) {
                        j += base;
                    }
                    while (j >= base) {
                        j -= base;
                    }
                    rpnstack->s[stptr - i] = tmp_stack[j];
                }
                free(tmp_stack);
            }
            break;
        case OP_INDEX:
            stackunderflow(0);
            {
                int       i = (int) rpnstack->s[stptr];

                stackunderflow(i);
                rpnstack->s[stptr] = rpnstack->s[stptr - i];
            }
            break;
        case OP_COPY:
        {
            int       base = (int) rpnstack->s[stptr--];
            int       i = base;

            stackunderflow(base - 1);
            /* allocate or grow the stack */
            while (stptr + base > rpnstack->dc_stacksize) {
                /* could move this to a separate function */
                rpnstack->dc_stacksize += rpnstack->dc_stackblock;
                rpnstack->s = (double *) rrd_realloc(rpnstack->s,
                                                     (rpnstack->dc_stacksize)
                                                     *
                                                     sizeof(*(rpnstack->s)));
                if (rpnstack->s == NULL) {
                    rrd_set_error("RPN stack overflow");
                    return -1;
                }
            }
            while (i--) {
                stptr++;
                rpnstack->s[stptr] = rpnstack->s[stptr - base];
            }
        }
            break;
        case OP_DEPTH:
            stptr++;
            rpnstack->s[stptr] = stptr;
            break;

        case OP_END:
            break;
        }
#undef stackunderflow
    }
    if (stptr != 0) {
        rrd_set_error("RPN final stack size != 1");
        return -1;
    }

    output[output_idx] = rpnstack->s[0];
    return 0;
}

/* figure out what the local timezone offset for any point in
   time was. Return it in seconds */
static int tzoffset(
    time_t now)
{
    int       gm_sec, gm_min, gm_hour, gm_yday, gm_year,
        l_sec, l_min, l_hour, l_yday, l_year;
    struct tm t;
    int       off;

    gmtime_r(&now, &t);
    gm_sec = t.tm_sec;
    gm_min = t.tm_min;
    gm_hour = t.tm_hour;
    gm_yday = t.tm_yday;
    gm_year = t.tm_year;
    localtime_r(&now, &t);
    l_sec = t.tm_sec;
    l_min = t.tm_min;
    l_hour = t.tm_hour;
    l_yday = t.tm_yday;
    l_year = t.tm_year;
    off =
        (l_sec - gm_sec) + (l_min - gm_min) * 60 + (l_hour - gm_hour) * 3600;
    if (l_yday > gm_yday || l_year > gm_year) {
        off += 24 * 3600;
    } else if (l_yday < gm_yday || l_year < gm_year) {
        off -= 24 * 3600;
    }
    return off;
}
