PMCONVSCALE(3)

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 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 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 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).