NAME

       ms_genfactmult - Generate SEED sample rate factor and multiplier

SYNOPSIS

       #include <libmseed.h>

       int  ms_genfactmult ( double samprate, int16_t *factor,
                             int16_t *multiplier );

       int  ms_ratapprox ( double real, int *num, int *den,
                           int maxval, double precision );

DESCRIPTION

       ms_genfactmult generates an appropriate SEED sample rate factor and multiplier pair from a
       double precision sample rate.  If samprate is positive it is expected to represent a  rate
       in samples/second, if negative is is expected to represent a period in seconds/sample.

       Non-integer  sample  rates  and  periods  are supported between 32767.0 and 1/32767.0.  An
       error will be returned for non-integer rates and periods outside this range.

       Integer sample rates and periods are supported between 1 and the  maximum  possible  value
       (32767  *  32767).   Values  from 1 to 32767 are represented directly.  Values larger than
       32767 are factored and represented exactly when possible and approximated otherwise,  with
       the discrepency becoming larger as the values reach the maximum possible value.

       The  factor  and  multiplier  are  int16_t because that is the integer size needed for the
       fixed section of the SEED data header.

       ms_ratapprox finds an approximate rational number for a real  through  continued  fraction
       expansion.   Given  a  double  precision  real  the  routine  tries  to find a rational in
       numerator (num) and denominator (den) form whose  absolute  values  are  not  larger  than
       maxval while trying to reach a specified precision.

RETURN VALUES

       ms_genfactmult returns 0 on success and -1 when value is outside of the supported range or
       error.

       ms_ratapprox returns the number of iterations performed.

AUTHOR

       Chad Trabant
       IRIS Data Management Center