PACK(3PVM)

🎀 PACK(3PVM) 🎀

okay bestie, welcome to PACK(3PVM) — this is the PVM Version 3.4 page about packing the active message buffer with arrays of prescribed data type. yes it's a mouthful. yes it slaps. let's go 💅

---

✨ NAME ✨

pvm_pack — pack the active message buffer with arrays of prescribed data type. that's the whole vibe. you're stuffing data into the buffer so it can go travel the network like the main character it is 🦋

---

🌸 SYNOPSIS 🌸

C — look at all these little guys:

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 — the retro cousin:

call pvmfpack( what, xp, nitem, stride, info )

---

🫶 PARAMETERS 🫶

• fmt — a printf-like format expression that says what to pack. peep the discussion section below for the deets 👀
• nitem — total number of items to be packed. NOT the number of bytes. we do not count bytes here bestie, we count items, and that's the whole point.
• stride — the stride used when packing the items. like, if stride = 2 in pvm_pkcplx, then every other complex number gets packed. iconic skip-every-other-number behaviour ✨
• xp — pointer to the beginning of a block of bytes. can be any data type, but it must match the corresponding unpack data type. no mixing, no matching, no exceptions.
• 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. here are your options, memorise them iykyk:
  • STRING — 0
  • BYTE1 — 1
  • INTEGER2 — 2
  • INTEGER4 — 3
  • REAL4 — 4
  • COMPLEX8 — 5
  • REAL8 — 6
  • COMPLEX16 — 7
• info — integer status code the routine hands back. anything less than zero means something went wrong 😭

---

💖 DESCRIPTION 💖

so every single one of the pvm_pk* routines packs an array of the given data type into the active send buffer. the args for each routine are: a pointer to the first item to be packed, nitem (the total number of items to pack from this array), and stride (the stride to use when packing). that's the formula, bestie, every time.

the one exception is pvm_pkstr() — it packs a NULL terminated character string by definition, so it does NOT need nitem or stride arguments. meanwhile 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 absolutely be packed — that's just a string with no characters before the terminating '\0'. BUT packing a null string pointer, (char *)0, is not allowed. don't do it. it's giving undefined chaos 🙈

if the packing is successful, info will be 0. if some error occurs, info will be < 0.

you can pack a single variable (not an array!) by setting nitem = 1 and stride = 1. slay, so simple ✨

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:

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)

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

---

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 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. cute.

---

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. so like. don't do that. match your types, bestie 💅

---

🌈 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. no cap, it just won't work, don't fight it 🙈

---

😭 ERRORS 😭

• PvmNoMem — Malloc has failed. the message buffer size has exceeded the available memory on this host. your machine said "i simply cannot" 💀
• PvmNoBuf — there is no active send buffer to pack into. try calling pvm_initsend before packing message. you forgot to set the stage, bestie 🎀
• 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. it's giving "too much" 😭

---

👑 SEE ALSO 👑

• pvm_initsend(3PVM)
• pvm_unpack(3PVM)
• pvm_send(3PVM)
• pvm_recv(3PVM)
• pvm_pkmesg(3PVM)

---

that's the whole page bestie, you ate it 🫶 this was PACK(3PVM) from PVM Version 3.4, dated 30 August, 1993 — vintage but still iconic, periodt 💅✨