Conversion.h

Classes

Conversion -- A class with general conversion definitions (full description)

class Conversion

Interface

Public Members

typedef unsigned int ValueFunction (void* to, const void* from, unsigned int nvalues)

typedef void* ByteFunction (void* to, const void* from, unsigned int nbytes)

static unsigned int boolToBit (void* to, const void* from, unsigned int nvalues)

static void boolToBit (void* to, const void* from, unsigned int startBit, unsigned int nvalues)

static unsigned int bitToBool (void* to, const void* from, unsigned int nvalues)

static void bitToBool (void* to, const void* from, unsigned int startBit, unsigned int nvalues)

static unsigned int valueCopy (void* to, const void* from, unsigned int nbytes)

static ByteFunction* getmemcpy()

static void* mymemcpy (void* to, const void* from, unsigned int nbytes)

Description

Review Status

Reviewed By:

Friso Olnon

Date Reviewed:

1996/11/06

Programs:

Tests:

tConversion

Synopsis

This class contains the general definitions for the Conversion classes.

It defines the signature for the functions converting from input to output format (e.g. from local to canonical format). There is a version where the number of values is given and a version where the number of bytes is given. The latter is there to be able to use memcpy as a conversion function (which will often be the case). Note that the signatures only differ in return value.
It defines functions to convert Bools to bits and vice-versa. These are used elsewhere to store Bools as space efficient as possible. Note that these functions are machine independent (they work on little and big endian machines).
It defines a private version of memcpy for compilers having a different signature for memcpy (e.g. ObjectCenter and DEC-Alpha).

Static functions in the classes CanonicalConversion, VAXConversion, and IBMConversion convert data from/to canonical, VAX, and IBM/360 format, resp..
Classes derived from DataConversion provide the same functionality in a polymorphic way.

Motivation

This provides a common place for definitions used elsewhere. It also provides a uniform interface to memcpy.

Member Description

typedef unsigned int ValueFunction (void* to, const void* from, unsigned int nvalues)

Define the signature of a function converting nvalues values from internal to external format or vice-versa. These functions are used in the IO framework , but are also used in the table system. Examples of such conversions are:
- local <-> canonical (when storing in canonical format)
- local <-> local (when storing in local format)
- binary <-> ASCII
It returns the number of bytes in external format. (For example the ToLocal/FromLocal functions in class CanonicalConversion return the number of bytes in canonical format).

typedef void* ByteFunction (void* to, const void* from, unsigned int nbytes)

Define the signature of a function converting from one format to another providing the number of bytes. It returns the to pointer (similar to memcpy). (For example the byteTo/FromLocalXXX functions in class CanonicalConversion.

static unsigned int boolToBit (void* to, const void* from, unsigned int nvalues)
static void boolToBit (void* to, const void* from, unsigned int startBit, unsigned int nvalues)

Convert a stream of Bools to output format (as bits). The variable startBit (0-relative) indicates where to start in the to buffer.

static unsigned int bitToBool (void* to, const void* from, unsigned int nvalues)
static void bitToBool (void* to, const void* from, unsigned int startBit, unsigned int nvalues)

Convert a stream of Bools to output format (as bits). The variable startBit (0-relative) indicates where to start in the from buffer.

static unsigned int valueCopy (void* to, const void* from, unsigned int nbytes)

Copy a value using memcpy. It differs from memcpy in the return value. This version has the ValueFunction signature, but it expects as input the number of bytes.

static ByteFunction* getmemcpy()

Get a pointer to the memcpy function.

static void* mymemcpy (void* to, const void* from, unsigned int nbytes)

A placeholder for the ObjectCenter or DEC-alpha memcpy or 64bit SGI Also added this for HPUX11 (2b provided in the makedefs) (because they do not use an unsigned int for nbytes).