.\" $Id: pvm_pack.3,v 1.1 1996/09/23 22:05:27 pvmsrc Exp $
.TH PACK 3PVM "30 August, 1993" "" "PVM Version 3.4"
.SH NAME
pvm_pack \- Pack the active message buffer with arrays
of prescribed data type.

.SH SYNOPSIS
.nf
.ft B
C
.br
	int info = pvm_packf( const char *fmt, ... )
.br
	int info = pvm_pkbyte( char *xp, int nitem, int stride )
.br
	int info = pvm_pkcplx( float *cp, int nitem, int stride )
.br
	int info = pvm_pkdcplx( double *zp, int nitem, int stride )
.br
	int info = pvm_pkdouble( double *dp, int nitem, int stride )
.br
	int info = pvm_pkfloat( float *fp, int nitem, int stride )
.br
	int info = pvm_pkint( int *ip, int nitem, int stride )
.br
	int info = pvm_pkuint( unsigned int *ip, int nitem, int stride )
.br
	int info = pvm_pkushort( unsigned short *ip, int nitem, int stride )
.br
	int info = pvm_pkulong( unsigned long *ip, int nitem, int stride )
.br
	int info = pvm_pklong( long *ip, int nitem, int stride )
.br
	int info = pvm_pkshort( short *jp, int nitem, int stride )
.br
	int info = pvm_pkstr( char *sp )

Fortran
.br
	call pvmfpack( what, xp, nitem, stride, info )
.fi

.SH PARAMETERS
.IP fmt 0.8i
Printf\-like format expression specifying what to pack. (See discussion).
.br
.IP nitem
The total number of \fIitems\fR to be packed
(not the number of bytes).
.\" For example, if nitem = 5 in pvm_pkdouble, then 5 double precision
.\" floating point values will be packed.
.br
.IP stride
The stride to be used when packing the items.
For example, if stride = 2 in pvm_pkcplx, then every other complex
number will be packed.
.br
.IP xp
Pointer to the beginning of a block of bytes. Can be any data type,
but must match the corresponding unpack data type.
.br
.IP cp
Complex array at least nitem*stride items long.
.br
.IP zp
Double precision complex array at least nitem*stride items long.
.br
.IP dp
Double precision real array at least nitem*stride items long.
.br
.IP fp
Real array at least nitem*stride items long.
.br
.IP ip
Integer array at least nitem*stride items long.
.br
.IP jp
Integer*2 array at least nitem*stride items long.
.br
.IP sp
Pointer to a null terminated character string.
.br
.IP what
Integer specifying the type of data being packed.
.ta 0.5i 2.0i 2.5i 4.0i
.nf
	\fIwhat\fR options
	STRING	0	REAL4	4
	BYTE1	1	COMPLEX8	5
	INTEGER2	2	REAL8	6
	INTEGER4	3	COMPLEX16	7
.fi
.IP info
Integer status code returned by the routine.
Values less than zero indicate an error.

.SH DESCRIPTION
Each of the pvm_pk* routines packs an array of the
given data type into the active send buffer.
The arguments for each of the routines are a pointer
to the first item to be packed,
.I nitem
which is the
total number of items to pack from this array, and
.I stride
which is the stride to use when packing.
.PP
An exception is pvm_pkstr() which by definition packs
a NULL terminated character string and thus does not need
.I nitem
or
.I stride
arguments.
The Fortran routine pvmfpack( STRING, ... ) expects
.I nitem
to be the number of characters in the string and
.I stride
to be 1.
.PP
A null string ("") can be packed;
this is just a string with no characters before the terminating '\\0'.
However,
packing a null string pointer, (char *)0, is not allowed.
.PP
If the packing is successful,
.I info
will be 0. If some error occurs then
.I info
will be < 0.
.PP
A single variable (not an array) can be packed by setting
.I nitem
= 1 and
.I stride
= 1.
.PP
The routine pvm_packf() uses a printf\-like format expression
to specify what and how to pack data into the send buffer.
All variables are passed as addresses if count and stride are specified
otherwise, variables are assumed to be values.
A BNF-like description of the format syntax is:
.br
    format : null | init | format fmt
.br
    init : null | '%' '+'
.br
    fmt : '%' count stride modifiers fchar
.br
    fchar : 'c' | 'd' | 'f' | 'x' | 's'
.br
    count : null | [0-9]+ | '*'
.br
    stride : null | '.' ( [0-9]+ | '*' )
.br
    modifiers : null | modifiers mchar
.br
    mchar : 'h' | 'l' | 'u'

Formats:
.nf
  +  means initsend - must match an int (how) in the param list.
  c  pack/unpack bytes
  d  integers
  f  float
  x  complex float
  s  string

Modifiers:
  h  short (int)
  l  long  (int, float, complex float)
  u  unsigned (int)

'*' count or stride must match an int in the param list.
.fi

.PP
Future extensions to the
.I what
argument in pvmfpack will include
64 bit types when XDR encoding of these types is available.
Meanwhile users should be aware that precision can be lost
when passing data from a 64 bit machine like a Cray to a
32 bit machine like a SPARCstation. As a mnemonic the
.I what
argument name includes the number of bytes of
precision to expect. By setting encoding to PVMRAW (see pvmfinitsend)
data can be transferred between two 64 bit machines with
full precision even if the PVM configuration is heterogeneous.
.PP
Messages should be unpacked exactly like they were packed
to insure data integrity.
Packing integers and unpacking
them as floats will often fail because a type encoding
will have occurred transferring the data between heterogeneous
hosts. Packing 10 integers and 100 floats then trying to
unpack only 3 integers and the 100 floats will also fail.

.SH EXAMPLES
.nf
C:
	info = pvm_initsend( PvmDataDefault );
	info = pvm_pkstr( "initial data" );
	info = pvm_pkint( &size, 1, 1 );
	info = pvm_pkint( array, size, 1 );
	info = pvm_pkdouble( matrix, size*size, 1 );
	msgtag = 3 ;
	info = pvm_send( tid, msgtag );
.sp
    int count, *iarry;
    double darry[4];
    pvm_packf("%+ %d %*d %4lf", PvmDataRaw, count, count, iarry, darry);
.sp
Fortran:
	CALL PVMFINITSEND(PVMRAW, INFO)
	CALL PVMFPACK( INTEGER4, NSIZE, 1, 1, INFO )
	CALL PVMFPACK( STRING, 'row 5 of NXN matrix', 19, 1, INFO )
	CALL PVMFPACK( REAL8, A(5,1), NSIZE, NSIZE , INFO )
	CALL PVMFSEND( TID, MSGTAG, INFO )
.fi

.SH WARNINGS
Strings cannot be packed when using the PvmDataInPlace encoding,
due to limitations in the implementation.
Attempting to pack a string using
pvm_pkstr or pvm_packf
will cause error code PvmNotImpl to be returned.
.SH ERRORS
.IP PvmNoMem
Malloc has failed. Message buffer size has exceeded
the available memory on this host.
.IP PvmNoBuf
There is no active send buffer to pack into.
Try calling pvm_initsend before packing message.
.IP PvmOverflow
Attempt to pack a value too large.
E.g. packing an 8-byte long with XDR encoding if the value won't fit into 4 bytes.
.PP
.SH SEE ALSO
pvm_initsend(3PVM),
pvm_unpack(3PVM),
pvm_send(3PVM),
pvm_recv(3PVM),
pvm_pkmesg(3PVM)