NAME

       pmConvScale - rescale a performance metric value

C SYNOPSIS

       #include <pcp/pmapi.h>

       int pmConvScale(int type, const pmAtomValue *ival, const pmUnits *iunit,
               pmAtomValue *oval, const pmUnits *ounit);

       cc ... -lpcp

DESCRIPTION

       All performance metric values may be encoded in a pmAtomValue union, defined as follows;

            typedef union {
                __int32_t    l;     /* 32-bit signed */
                __uint32_t   ul;    /* 32-bit unsigned */
                __int64_t    ll;    /* 64-bit signed */
                __uint64_t   ull;   /* 64-bit unsigned */
                float        f;     /* 32-bit floating point */
                double       d;     /* 64-bit floating point */
                char         *cp;   /* char ptr */
                pmValueBlock *vbp;  /* pmValueBlock ptr */
            } pmAtomValue;

       The encoding of a performance metric's dimensionality and scale uses a pmUnits  structure;
       see pmLookupDesc(3).

       Given  a  performance  metric  value  pointed to by ival multiply it by a scale factor and
       return the value in oval.  The scaling takes place from the units defined  by  iunit  into
       the   units   defined  by  ounit.   Both  input  and  output  units  must  have  the  same
       dimensionality.

       The performance metric type for both input and output values is determined  by  type,  the
       value  for  which  is  typically  extracted  from  a pmDesc structure, following a call to
       pmLookupDesc(3) for a particular performance metric.

       pmConvScale is most useful when values returned via pmFetch(3),  (and  possibly  extracted
       using pmExtractValue(3)) need to be normalized into some canonical scale and units for the
       purposes of computation.

       As a special case, if all components of the dimension are zero, then this  is  treated  as
       synonymous  with  a  ``count''  dimension  of  one,  and so the ``count'' scale components
       determine the relative scaling.  This accommodates the case where performance metrics  are
       dimensionless, without special case handling on the part of the caller.

DIAGNOSTICS

       PM_ERR_CONV

              iunit and ounit have different dimensionality, or have inappropriate type

       PM_ERR_UNIT

              Inappropriate iunit or ounit parameter

SEE ALSO

       PMAPI(3),  pmAtomStr(3),  pmExtractValue(3), pmFetch(3), pmLookupDesc(3), pmPrintValue(3),
       pmTypeStr(3) and pmUnitsStr(3).