PACK(3PVM) PVM Version 3.4 PACK(3PVM)NAME
pvm_pack - Pack the active message buffer with arrays of prescribed
data type.
SYNOPSIS
C
int info = pvm_packf( const char *fmt, ... )
int info = pvm_pkbyte( char *xp, int nitem, int stride )
int info = pvm_pkcplx( float *cp, int nitem, int stride )
int info = pvm_pkdcplx( double *zp, int nitem, int stride )
int info = pvm_pkdouble( double *dp, int nitem, int stride )
int info = pvm_pkfloat( float *fp, int nitem, int stride )
int info = pvm_pkint( int *ip, int nitem, int stride )
int info = pvm_pkuint( unsigned int *ip, int nitem, int stride )
int info = pvm_pkushort( unsigned short *ip, int nitem, int stride )
int info = pvm_pkulong( unsigned long *ip, int nitem, int stride )
int info = pvm_pklong( long *ip, int nitem, int stride )
int info = pvm_pkshort( short *jp, int nitem, int stride )
int info = pvm_pkstr( char *sp )
Fortran
call pvmfpack( what, xp, nitem, stride, info )
PARAMETERS
fmt Printf-like format expression specifying what to pack. (See
discussion).
nitem The total number of items to be packed (not the number of
bytes).
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.
xp Pointer to the beginning of a block of bytes. Can be any data
type, but must match the corresponding unpack data type.
cp Complex array at least nitem*stride items long.
zp Double precision complex array at least nitem*stride items
long.
dp Double precision real array at least nitem*stride items long.
fp Real array at least nitem*stride items long.
ip Integer array at least nitem*stride items long.
jp Integer*2 array at least nitem*stride items long.
sp Pointer to a null terminated character string.
what Integer specifying the type of data being packed.
what options
STRING 0 REAL4 4
BYTE1 1 COMPLEX8 5
INTEGER2 2 REAL8 6
INTEGER4 3 COMPLEX16 7
info Integer status code returned by the routine. Values less than
zero indicate an error.
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, nitem which is the total number
of items to pack from this array, and stride which is the stride to use
when packing.
An exception is pvm_pkstr() which by definition packs a NULL terminated
character string and thus does not need nitem or stride arguments. The
Fortran routine pvmfpack( STRING, ... ) expects nitem to be the number
of characters in the string and stride to be 1.
A null string ("") can be packed; this is just a string with no charac‐
ters before the terminating '\0'. However, packing a null string
pointer, (char *)0, is not allowed.
If the packing is successful, info will be 0. If some error occurs then
info will be < 0.
A single variable (not an array) can be packed by setting nitem = 1 and
stride = 1.
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, vari‐
ables are assumed to be values. A BNF-like description of the format
syntax is:
format : null | init | format fmt
init : null | '%' '+'
fmt : '%' count stride modifiers fchar
fchar : 'c' | 'd' | 'f' | 'x' | 's'
count : null | [0-9]+ | '*'
stride : null | '.' ( [0-9]+ | '*' )
modifiers : null | modifiers mchar
mchar : 'h' | 'l' | 'u'
Formats:
+ 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)
Future extensions to the 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 what argument name includes the number of bytes of preci‐
sion 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.
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.
EXAMPLES
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 );
int count, *iarry;
double darry[4];
pvm_packf("%+ %d %*d %4lf", PvmDataRaw, count, count, iarry, darry);
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 )
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.
ERRORS
PvmNoMem
Malloc has failed. Message buffer size has exceeded the avail‐
able memory on this host.
PvmNoBuf
There is no active send buffer to pack into. Try calling
pvm_initsend before packing message.
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.
SEE ALSOpvm_initsend(3PVM), pvm_unpack(3PVM), pvm_send(3PVM), pvm_recv(3PVM),
pvm_pkmesg(3PVM)
30 August, 1993 PACK(3PVM)
