.TH MS_GENFACTMULT 3 2016/10/07 "Libmseed API"
.SH NAME
ms_genfactmult - Generate SEED sample rate factor and multiplier

.SH SYNOPSIS
.nf
.B #include <libmseed.h>

.BI "int  \fBms_genfactmult\fP ( double " samprate ", int16_t *" factor ",
.BI "                      int16_t *" multiplier " );"

.BI "int  \fBms_ratapprox\fP ( double " real ", int *" num ", int *" den ",
.BI "                    int " maxval ", double " precision " );"
.fi

.SH DESCRIPTION
\fBms_genfactmult\fP generates an appropriate SEED sample rate
\fIfactor\fP and \fImultiplier\fP pair from a double precision sample
rate.  If \fIsamprate\fP 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.

\fBms_ratapprox\fP finds an approximate rational number for a real
through continued fraction expansion.  Given a double precision
\fIreal\fP the routine tries to find a rational in numerator
(\fInum\fP) and denominator (\fIden\fP) form whose absolute values are
not larger than \fImaxval\fP while trying to reach a specified
\fIprecision\fP.

.SH RETURN VALUES
\fBms_genfactmult\fP returns 0 on success and -1 when value is outside
of the supported range or error.

\fBms_ratapprox\fP returns the number of iterations performed.

.SH AUTHOR
.nf
Chad Trabant
IRIS Data Management Center
.fi