# pmConvScale - Man Page

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).

## Referenced By

PCPIntro(3), PMAPI(3), pmAtomStr(3), pmExtractValue(3), pmLookupDesc(3), pmParseUnitsStr(3), pmPrintValue(3), pmSemStr(3), pmTypeStr(3), pmUnitsStr(3).