Distribution Update History of the SPIN sources
===============================================

==== Version 3.0.0 - 12 August 1997 ====

A new release, a new V3.Updates file.  See the end
of the V2.Updates file for the main changes between
the last version 2.9.7 and the new version 3.0.0.

Spin Version 1 lasted from Jan. 1990 - Jan.   1995.
Spin Version 2 lasted from Jan. 1995 - August 1997.

The shell script upgrade2 will take any version of
Spin between version 2.7 and 2.9 to version 3.0.
Upgrades from 3.0 forward will appear in a new shell
script upgrade3, to keep the file small.

==== Version 3.0.1 - 19 August 1997 ====

- on older PC's the hashing behavior could be substandard.
  on those systems an int is often interpreted as a 16 bit,
  instead of a 32-bit quantity.  the fix made is to declare
  the relevant variables as long integers instead of plain
  integers. there is no visible difference for other systems.
- printf accidentily picked up a redundant newline in 3.0.0
  it is gone again.
- interactive use of spin models with rendez-vous statements
  could get hung in some cases.

==== Version 3.0.2 - 24 August 1997 ====

- improved the fix for interactive use of rv's from 3.0.1
- the parser now catches the use of 'run' to initialize
  global variables as an error.
- the parser now catches the use of any initializer on
  a formal parameter in a proctype as an error.
- addition of a new datatype to Promela: unsigned
  usage:
	unsigned name : 3;
  declares 'name' to be a variable that can hold unsigned
  values -- stored in 3 bits (i.e., values 0..7 inclusive).
  values outside the declared range are truncated to the
  range on assignments
- d_step may now appear inside and atomic and vice versa
- extra option -E to pass arguments to the C preprocessor
  usage:
	spin -E-Dfoo=faa filename
  to redefined foo as faa in the filename
	spin -Pmy_cpp -E-E filename
  use my_cpp as the preprocessor (replacing cpp) and
  pass it flag -E when it is called.

==== Version 3.0.3 - 8 September 1997 ====

- unsigned variables weren't cast correctly during
  simulation runs --
- warnings about variables being of too generous a type
  are now only generated when the -v verbose option is set
- extra warnings, on use of channels, are now also
  generated with spin -v -- still more with spin -v -g 
- can now pass directives to the preprocessor with a simpler
  spin option -D..., e.g., spin -DLOSS=1 spec
  the earluer -E-D... also still works
- a few more additions to xspin303.tcl

==== Version 3.0.4 - 25 October 1997 ====

- now accepts truncated extensions of pan.trail
  (often visible only as pan.tra) on PCs
- now recognizes compiler directive __FreeBSD__
- redundant include file <malloc.h> deleted from main.c
- now properly initializes all channels hidden in typedef
  structures
- made it possible to generate structural views of the
  promela model, but tracking channel uses (more to come)
- added pc_zpp.c to the sources - used only on the pc

==== Version 3.0.5 - 5 November 1997 ====

- corrected bug in the builtin macro preprocessor of the
  PC-version (only) of spin.  if the first literal match
  of the macro source failed to be a valid replacement string,
  no further matches were tried on that line
- corrected bug in interactive simulation mode that could
  cause a failure to return control to the user

==== Version 3.0.6 - 16 December 1997 ====

- a value that is truncated in an assignment to a variable
  of a small type triggered an error message that sometimes
  could cause xspin to miss a display update for the variable
  values pannel.
- on a -c flag spin was a little too talkative, assuming also
  a -v verbose flag for the final detail printed at the end of
  a simulation run.
- fixed an error in the processing of logical OR in the presence
  of the X operator in LTL formulae -- this only affected the
  outcome of a translation if Spin was compiled with -DNXT
  to enable the LTL next-time operator (this is not enabled by
  default, because it jeopardizes compatibility with the partial
  order reductions)
- a check for non-progress, in combination with provided clauses
  on proctypes, could fail. the omission was that the never claim
  process searched for its own provided clause, which should in
  this case default to true.
- the restriction that the use of any provided clause voided the
  partial order reduction was much too strict: it suffices to mark
  all statements in only the proctype that is labeled with a
  provided clause unsafe -- other processes are not affected.
- added new Test/pathfinder example to the Test directory,
  illustrating the use of provided clauses
- the standard stutter extension on finite sequences is not
  allowed to produce non-progress cycles, but in combination with
  the weak-fairness option this erroneously could happen.
  (stutter-extension on temporal claim matches is only applied
  to standard acceptance properties, under runtime option -a)
- there was an error in the implementation of weak fairness
  that could cause the algorithm to miss matching acceptance or
  non-progress cycles with weak-fairness enabled.  a small change
  in the implementation of this option (incrementing the Choueka
  counter values by 1) repairs this flaw.

==== Version 3.0.7 - 18 December 1997 ====

- the check on a self-loop, added in 3.0.6, unintentionally also
  ruled out self-loops in never claims, which are harmless (e.g.,
  to allow for a finite prefix of 'true' propositions).

==== Version 3.0.8 - 2 January 1998 ====

- with fairness enabled, a process was considered to be temporarily
  blocked while other processes performed a rv handshake.  this
  could cause a cycle to be reported as fair that normally would not
  be considered as such. fairness rule 2 was updated to avoid this.
- an assignment beginning a dstep sequence was incorrectly considered
  to be executable in the middle of a rendezvous handshake in progress
  elsewhere.

==== Version 3.0.9 - 11 January 1998 ====

- rendezvous communications lacked an arrow in the new postscript
  output generated with spin option -M
- new predefined channel name STDIN for reading a character from
  the standard input as in:
	chan STDIN;
	short c;
	do
	:: STDIN?c ->
		if
		:: c == -1 -> /* EOF */
			break
		:: else ->
			printf("%c", c)
		fi
	od
- to match this, added support for recognizing character
  symbols in Promela such as 'i', '\n', '\t', '\r', etc.
- fixed the bug that prevented weak fairness from being
  turned off during verifications.... (bug introduced in 3.0.8)
- small improvements in error catching (mostly related to
  illegal structure references)

==== Version 3.1.0 - 27 January 1998 ====

- all transitions from a local process state that is referenced
  within the never claim (or ltl property) are now properly labeled
  as unsafe in the partial order reduction
- a d_step that appears at the last statement in a proctype no longer
  generates an error in the simulator
- the predefined variable _last is now updated correctly during the
  verification process (thanks Pedro Merino for the examples)
- weak fairness is now considered incompatible with partial order reduction
  in models that contain rendezvous operations (thanks Dennis Dams for
  the example that revealed this)

==== Version 3.1.1 - 28 January 1998 ====

- fixed a goof in pc_zpp.c -- only visible in the precompiled PC
  version.  symptom: it would fail to expand some macros with the
  builtin version of cpp.  in particular, it would fail on the
  testcase: Test/leader from the distribution (thanks Mike Ferguson).

==== Version 3.1.2 - 14 March 1998 ====

- added a Cut/Copy/Paste meny to the text window of xspin version 3.1.2
  (big convenience), plus a few smaller fixes
- the verifiers generated by spin have two extra run-time options:
	-E to ignore all invalid endstate errors
	-A to ignore all assert() violations
- added #include <strings.h> to pan.c
- main in pan.c is now properly typed 'int' instead of 'void'
- the following change, introduced in 2.9.0, was unnecessary
	- assignments to channel variables can violate xr/xs assertions.
	  there is now a check to catch such violations
  the check is removed:
  when an xr channel variable is assigned to, it's old value is simply lost.
  it was the old value (operations on the channel that the value pointed
  to) that the xr/xs assertion applied to, not to the variable name as such.
  operations on the new channel id that the variable now points to
  are subject to the same xr/xs claims as the old one did.
- new argument to spin:
	spin -N claimfile ... promelaspec
  reads the never claim from 'claimfile'
  (the main filename 'promelaspec' is always the last argument)
- new argument to spin
	spin -C promelaspec
  prints some channel access info on stdout, useful for producing
  a structural view of the system
  (used to be an added output in spin -v)
- fixed bug in pan.c that caused some states created during claim stutter
  from not being removed from the dfs stack.  should rarely have occured.
- all the above extensions are supported in Xspin 3.1.2
- redesigned Xspin's LTL properties management dialogue panel
- fixed problem with hanging of long simulations on pc's
  (a buffer overflow problem internal to windows95/nt)

==== Version 3.1.3 - 16 March 1998 ====

- small bug fix in sym.c -- reported too many variables as
  unused on a spin -a -v spec
- small bug fix in xspin312.tcl -- replaced "else if" with "elseif"
- both bugs reported by Theo Ruys within hours after the release of 3.1.2
  thanks Theo!

==== Version 3.2.0 - 7 April 1998 ====

- a modest extension of the language:
  there is now a procedure-like construct that should reduce the need
  for macros.  Promela 'inline' functions preserve linenumber
  references in simulations (at least, that's the idea).
  an inline definition look like this (appearing outside all proctypes)

	inline functionname(x, y) {
		...a promela fragment...
	}

  a call looks like this -- and can appear wherever a statement can appear:

	functionname(4, a);

  the replacement text is inlined by the parser, with proper parameter
  matching and replacement.
  inlines can be recursive (one inline can call another), but not cyclic.

  there is still no local scope for variables.  this means that the scope
  of any local variable declared is always the entire proctype body --
  no matter where it is declared.
  local variables may be declared at the start of an inline -- but such
  variables have the same status as a local variable at the place of the call.

- added an example to the Test directory, illustrating inlines (Test/abp)

- timeout is no longer automatically enabled and available as a
  user-selectable option during interactive simulation.  it could cause
  counter-intuitive behavior, e.g. when the timeout was used in an unless-
  escape
- 'else' is now flagged as unexecutable when appropriate during interactive
  simulations -- where possible it is offered as a choice so that an
  execution can be forced in a given direction.
- small fixes and fiddles with xspin

==== Version 3.2.1 - 4 July 1998 ====

- added compile time directive HC, for a version of Wolper's hash-compact
  algorithm.  it can speed up the search, and reduce memory requirements,
  with a relatively low probability of hash-collisions (or missed states).
  this is a modification of exhaustive search where we store a 32-bit
  hash-value in the hash-tables, as a compressed state vector.
  the effective size of the compressed state-vector is the width of the
  hash-table itself (controlled by the runtime -w parameter) plus 32 bits
  (by default this is: 18+32 = 50 bits of information).
  the hash-table entries have some additional overhead which pushes total
  memory usage slightly higher -- but the memory reductions can be quite
  substantial (depending, trivially, on the length of the state vector
  without compression)
  to enable: compile pan.c with -DHC (perferably combined with -DSAFETY)
- fixed fgets problem discovered by Theo Ruys
  (problem: newlines could accidentily be added to the input text)
- fixed two bugs in dstep code generated in pan.c; improved error reporting
- fixed bug in processing of include files, when an ltl claim is used

==== Version 3.2.2 - 21 July 1998 ====

- generalized the hash-compact implementation
  by default (compiling pan.c with -DHC) 6 bytes are stored:
  4 bytes from the first hash and 2 bytes from a second hash
  this gives 32+16 = 48 bits of information, which should secure
  a very low collision probability
  alternatives are -DHC0 (for 32 bits) -DHC1 (for 40 bits) -DHC2 (48 bits)
  and -DHC3 (56 bits).
- reversed the order in which the transitions in a never claim are
  generated -- this tends to shorten the counter-examples generated
  (by putting the 'true' self-loops that at the end of the list, rather
  than at the beginning).  Thanks to Dragan Bosnacki.
- fixed a bug in xspin.tcl that could cause the application to hang
  when used on a PC (e.g., any simulation of leader...).
  (this synchronization bug was introduced in 3.1.4.)

==== Version 3.2.3 - 1 August 1998 ====

- an atomic that ends with a jump into another
  atomic sequence, now connects correctly without
  breaking atomicity
- the choice of a rendezvous partner for send operations
  wasn't random during simulations (when multiple targets
  for the rendezvous are available).  it is now.
- fix in xspin to avoid confusion between proctype names
  with a common prefix, in rendering an automaton view
- fix in pc_zpp.c for occasional incorrect comment processing
  and incorrect #define processing (affected the PC version only)

==== Version 3.2.4 - 10 January 1999 ====

modifications:
- replaced type "unsigned" in parameter to Malloc and emalloc
  with "unsigned long long" to support 64 bit word size machines
  (thanks to Judi Romijn's experiments at CWI)
  (may not be recognized by non-ansi standard c-compilers)
extensions:
- added a runtime flag -J for both spin (simulations) and
  for pan (verification runs), to specify that nested unless
  clauses are to be evaluated in reverse order from the default
  (to match java semantics of catch clauses) at the request
  of Klaus Havelund.
- added runtime flags -qN and -B for spin (simulations)
  -q4 suppresses printing output related to queue 4
  -B suppresses printing the final wrapups at the end of a run
- added runtime flag -v for pan (verification) to add filenames
  to linenumbers in the listings of unreached states (xspin does
  not support these extensions yet)
bug-fixes:
- a very long source statement could overflow an internal
  buffer in pan.c, upon the generation of a trail-file.
  (thanks for Klaus Havelund's experiments with a java->spin
   translator)
- compilation with a vectorsize greater than 1024 could cause
  the model checker to behave incorrectly in cases when receive
  statements were used that received data into global variables
  (instead of locals).  this now works correctly.
- removed bug in the optimization code of the ltl-translation
  algorithm -- it could remove untils in cases such as
  p /\ (q U r) not only if p==r, but also if p appeared within r
- line numbers could be inaccurate if #if 0 ... #endif directives
  were used inside inline declarations.  corrected.
- fixed a bug in ltl translation due to a failure to recognize
  'true' to be part of any 'and' form -- should have been a rare
  occurrence.
- fixed a bug that affected the use of rendezvous statements in
  the guard of an escape clause of an unless

==== Version 3.3.0 - 1 June 1999 ====

- rearranged code to share code for identical cases
  in pan.m and pan.b -- this reduces the file sizes by up
  to 60% and similarly reduces compilation times for pan.c
- added pan.c compiler directive MEMLIM
  compiling pan.c with -DMEMLIM=N will restrict memory use
  to N Megabytes precisely;  this is an alternative to the
  existing limit -DMEMCNT=N which restricts to 2^N bytes
  and gives less precise control.
- added new data declaration tag 'local' which can be used
  wherever currently 'show' or 'hidden' can be used.
  it allows one to identify global variables that are
  effectively local (used by only 1 process) as data objects
  of which manipulation is safe for partial order reductions.
  there's no check for the validity of the tag during verification.
- automatically hide unused or write-only variables
  option can be turned off with spin option -o2
- eval() (used in receive statements to turn a variable into
  a constant value) can now contain an arbitrary expression,
  instead of just a name (request of Victor Bos).
- it is no longer an error to have multiple mtype definitions
  (they are catenated internally)
- more verbose error-trails during guided simulations - in verbose
  mode it now includes explicit mention of never claim moves, if
  a never claim is involved
- added also an experimental option to generate code separately
  for the main system and for the never claim - this makes
  separate compilation possible.  the option will be finetuned
  and documented once it has settled.  for the time being, they
  are not listed in the usage listings.
- also added, but not enabled, fledgling support for a bisimulation
  reduction algorithm that might be applied to never claims to
  reduce their size (inspired by work of Kousha Etessami),

- bugfixes (the first two found by Wenhui Zhang):
  - in fairness option (could miss a fair cycle)
  - in implementation of the -DMA option (could incorrectly
    claim an intersection of the 1st dfs stack an declare a
    cycle when none existed)
  - in the conversion of ltl formulae to automata (could
    occassionaly fail to match common subexpressions)
  - bug fix in the runtime code for random receive, fixed
  - fixed execution of atomics during interactive simulation
  - fixed possibly erroneous marking as 'dead' variables used
    to index a structure variable array

- during interactive simulation, to avoid confusion, choices
  between different *escapes* on a statement are no longer offered
  in user menus, but are now always resolved by the simulator
- removed all uses of "long long" and replace with "long."
  the former (temporarily used in 3.2.4) is not in ansi c,
  and the latter will be interpreted correctly on 64bit machines
  by a 64bit compiler.
- added better support for 64bit machines -- avoiding deteriorated
  performance of the hashing algorithms (courtesy Doug McIlroy)
- the pc version could get the linenumber references wrong after
  multiline comments - now repaired (courtesy Mike Ferguson)
- removed bug in xspin.tcl that prevented the selection of
  bitstate hashing from the ltl properties manager panel
  (courtesy Theo Ruys)
- added an option in xspin to exclude specific channels from the
  msc displays (you have to know the channel number though)
- fixes in the interactive simulation model (courtesy Judi Romijn)
  - d_steps and atomics now always run to completion without
  prompting the user for intermediate choices that could break
  the atomicity (and the semantics rules).
  - unless escapes no longer reach inside d_steps (they do reach
  inside atomics)
- merges sequences of safe or atomic steps -- a considerable speedup
  this behavior can be disabled with spin option -o3
- computes precondition for feasibility of rv - this option can be
  enabled with spin option -o4 -- it seems of little use in practice
- dataflow analysis -- can be disabled with spin option -o1
- partial evaluation to remove dead edges from verification model
  (i.e., with a constant 'false' guard)
- added pan compile time option -DSC to enable new stack cycling option.
  this will swap parts of deep stacks to a diskfile with only low overhead.
  it needs no further user action to work -- the runtime -m flag
  remains, but now simply sets the size of the part of the stack
  that is in core (i.e., you need not set it explicitly unless you want to)
- added pan compile time option -DLC to optinally use hashcompacted stackstates
  during Bitstate runs. it is slower by about 20-30%, but in cases
  where -DSC is used (very deep stacks) it can safe a lot of extra memory.
  for this reason -DSC always enables -DLC by default

==== Version 3.3.1 - 12 July 1999 ====

- fix in pangen2.h, to avoid a null-pointer reference
  in the automata preparation routines. it can occur in some cases
  where progress labels are used in combination with p.o. reduction
- fix for weak-fairness in combination with p.o. reduction and
  unless/rendez-vous (courtesy Dragan Bosnacki)
- fix to prevent an infinite cycle during the weak-fairness based
  verifications. (when both the 2nd and the 1st dfs stacks are
  intersected with a non-zero choueka counter value, the search
  used to continue - instead this should be treated as a regular
  stack match)
- better feedback on spin -a when parts of the automaton are pruned
  due to constant false guards
- added spin option -w (extra verbose) to force all variable
  values to be printed at every execution step during simulations

==== Version 3.3.2 - 16 July 1999 ====

- correcting an initially erroneous fix in 3.3.1 that prevented
  compilation alltogether for sources generated through xspin. (...)
  (it left a reference to counters used in the weak fairness algorithm
   in the code that had to be suppressed if weak fairness isn't used)

==== Version 3.3.3 - 21 July 1999 ====

- fix in the new code for dataflow analysis. in some cases a core-dump
  could result if a particular control-flow structure was encountered
  (courtesy Klaus Havelund)
- updated Xspin to 3.3.3 to deal with the new policy in 3.3 that printfs
  during simulations are always indented by a number of tab-stops that
  corresponds to the process number of the process that executes the
  printf - this makes printfs from the same process line up in columns,
  but it confused xspin.  (fix courtesy of Theo Ruys)

==== Version 3.3.4 - 9 September 1999 ====

- new pan option -T to prevent an existing trail file from being
  overwritten (useful if you run multiple copies of pan with
  bitstate hashing and different -w parameters, to optimize chances
  of finding errors fast -- the first run to write the trail file
  then wins)
- small improvement in error reporting for use of special labels inside
  atomic and d_step sequences
- small portability change to avoid problems with some compilers (e.g.
  the ones used on plan9)
- increased some statically defined maxima (e.g. for the max length of
  a single statement - now increased to 2K bytes to avoid problems with
  machine generated Promela files)

==== Version 3.3.5 - 28 September 1999 ====

- two bug-fixes in the ltl->never claim conversion (with thanks to
  Heikki Tauriainen for reporting them)
- increase in some static buffer sizes to allow for long
  (typically machine generated) variable names
- removed some debugging printfs

==== Version 3.3.6 - 23 November 1999 ====

- two small extensions and 4 important bug fixes

- added runtime option -t to pan;  using pan -tsuf will
  cause error trails to be written into spec.suf instead of
  spec.trail (which remains the default)
- added a verbose output to the verification runs, to write
  a line of output each time a new state in the never claim
  is reached.  this helps keeping track of progress in long
  running verifications -- and helps to avoid false positives
  (i.e., when most states in the never claim are unreached,
  which is a strong indication that the LTL formula that
  produced the claim isn't related to real behavior of the
  system)

- bug fix in the fairness algorithm (-f flag during verification)
  that could cause false error reports to be generated
- bug fix in the stack cycling compile-time option to pan.c (-DSC)
  which could cause erroneous behavior of the verifier
  (both of these reported by Muffy Calder and Alice Miller)
- bug fix in the generation of never claims from LTL -- missing
  parentheses around subexpressions in a guard
- fix to circumvent buggy behavior from gcc on Unix platforms
  (its version of sbrk can return memory that is not properly
   word aligned -- which causes memory faults in pan)

==== Version 3.3.7 - 6 December 1999 ====

- 3.3.6 introduced a bug that prevented the verifier code
  from compiling unless fairness was enabled -- corrected in 3.3.7
- fixed a minor problem with the as yet unadvertised separate
  compilation option (compiling the program separately from
  the claim to speed up verifications of multiple claims)
- fixed a bug in the simulation code that could make the
  simulator miss executing statements. it could lead to
  misleading traces for errors. (thanks to an example by Pim Kars)

==== Version 3.3.8 - 1 January 2000 ====

- fixed a bug in the simulation code that caused no output
  to appear, for instance, when the traceback is done with
  a guided simulation for the Test/loops testfile -- fixed
- fixed bug in the generation of ltl formula of the type:
	<>[]p && []<>q && []<>r
  traced to a mistake in the comparison of states in the
  buchi automaton that could unjustly claim two states to
  be identical even if they differed (reported by Hagiya)
- added a cast to (double) for manipulation of MEMLIM to
  avoid problems with some compilers
- added a small optimization that rids the spec of repeated
  sequential skip statements, or skips immediately following
  printfs (these may be present in mechanically generated specs)

==== Version 3.3.9 - 31 January 2000 ====

- fixed several more bugs in the ltl -> buchi automata
  conversion - found with a random testing method
  described by Heikki Tauriainen. the method consists
  of generating random ltl formula with a fixed number of
  propositional symbols, with varying numbers of operators,
  and generating random statespaces over the boolean
  operands, up to preset maximum number of states.
  we've done tests with three databases, consisting of:
	- 27 handpicked standard ltl formulae with up to 4
	  operands
	- 5356 random ltl formulae with up to 10 temporal
	  operators and up to 3 operands
	- 20577 ltl formulae with up to 3 temporal operators
	  and up to 3 operands
  each formula was tested for 25 randomly generated statespaces
  with up to 50 global states.
  we checked spin's automata generation method against an
  independent implementation by kousha etessami, and verified
  that each of the tests either failed with both tools or
  passed with both tools -- any difference pointed to a bug
  in one of the two tools.
  the fixes in spin version 3.3.9 are mostly related
  to the use of the X (next operator -- which is normally
  disabled but can be enabled by compiling the spin sources
  with the extra compiler directive -DNXT) and V (the dual
  of U) in long formula.
- used the opportunity to add in some more optimizations
  that reduce the size of the automata that are produced
  (which in many cases also speeds up the generation process).
  the optimizations were inspired by kousha etessami's work.
  (email: kousha@research.bell-labs.com)

==== Version 3.3.10 - 15 March 2000 ====

- this should be a final, stable release of spin
  version 3.3, barring the unforeseen.
  we'll move to 3.4.0 in a next round of extensions.

- made the number of active processes a globally visible
  read-only variable: _nr_pr
  this makes it possible to start a process and then wait
  for it to complete:
	run A(); (_nr_pr == _pid+1);
  useful for simulating function calls.
- the appearance of a timeout in the guard of a d_step
  sequence was treated as an error - it is not treated
  as a warning. (in the guard a timeout is ok)
- fixed rounding error in calculating the nr of bytes
  to be stored in statevector with -DCOLLAPSE option.
  in rare cases the roundoff error could result in
  missed states when collapse was enabled. reported by
  Dragan Bosnacki.
- improved ltl->buchi automata conversion some more
  to be described in an upcoming paper by kousha.
- small update of xspin.tcl -- it failed to record spin
  command line options in the advanced verification options
  panel. reported by Theo Ruys.

==== Version 3.4.0 - 14 August 2000 ====

- fixed two remaining problems with the ltl conversion
  algorithm, related to nested untils and the use of the next
  operator (thanks again Heikki Tauriainen).
- deals better with renaming files for preprocessing -- no
  longer relies on temporary files residing on the same
  filesystem as the working directory
- added an alignment attribute for the State vector to force
  gcc to align this structure on a wordboundary (on solaris
  machines gcc apparently considers this optional).
- fixed two problems in the use of trace-assertions (could
  fail when tracking actions on rendezvous channels)
- new xspin340.tcl that deals better with non-terminating
  simulation runs on pcs.
- added support for property-based slicing, to be documented.
  one example in the Test directory illustrates its use: the
  wordcount example.
- added two examples (mobile[12]) that show how specifications
  in the pi-calculus can be rendered in Promela (thanks Joachim
  Parrow).

==== Version 3.4.1 - 15 August 2000 ====

- fixed problem with spin option -m -- it stopped working after
  the upgrade to spin 3.3.0 a year ago. (Thanks Theo Ruys and Rui Hu).
- minor twiddles to avoid some spurious warnings from gcc on pan_ast.c

==== Version 3.4.2 - 28 October 2000 ====

- release 3.4.1 had some windows carriage returns in some of the
  source files, which unix compilers don't like - removed
- two small fixes in the data dependency algorithm, e.g. to make sure
  that an array index is never considered a def
- made the allignment attribute on the State struct GCC specific
  (which it is -- used only on Solaris)
- the -o2 flag didn't work as advertised, fixed.
- fix to prevent problems with too liberal use of sequence brackets
  which could cause a coredump in some cases

==== Version 3.4.3 - 22 December 2000 ====

- small bug fixes, related to the use of {...} for plain sequences
  (other than for atomic or d_step sequences), and the use of
  enabled to refer to the running process in simulation mode

==== Version 3.4.4 - 2 February 2001 ====

- fix of the trace assertion code in pan.c (there was a problem
  when trace assertions were used in combination with rv operations)
- fix of marking of unreachable states (some reached states could
  erroneously be reported as unreached in some cases)

==== Version 3.4.5 - 8 March 2001 ====

- one more bug found by Heikki Tauriainen - in the LTL -> Buchi
  conversion algorithm. it was caused by an unjustified optimization
  in tl_rewrt.c -- now commented out.

==== Version 3.4.6 - 29 March 2001 ====

- when using rendezvous channels, the compression mask was
  not completely restored on backward moves during the search.
  the correctness of the search was not affected, but the
  number of reached states became larger than necessary
  (up to twice as large as needed). bug fixed.
  (found and reported by Vivek Shanbhag)

==== Version 3.4.7 - 23 April 2001 ====

- fixed a number of small bugs in xspin.tcl (now version 3.4.7)
  (shaded out menu items were not enabled, errors on cancel of
   simulation runs, etc.)
- pruned the number of unreached states reported, by removing
  reports for internal states (marked ".(goto)" or "goto :b3")
- fixed bug in pid assignements on guided simulation for np-cycles

==== Version 3.4.8 - 22 June 2001 ====

- more small bug fixes
  e.g., a problem with parameters on inline calls, if the name
  of an actual parameter equals the name of another formal parameter
  in the same inline; a typo in an 'attribute' annotation; some
  missing parameters in rarely executed printf calls

==== Version 3.4.9 - 1 October 2001 ====

- two bug fixes:
  - problem with xr/xs declarations for processes that can be
  instatiated with multiple pids -- could lead to a coredump
  - problem with treatment of merged statements in guided simulations.
  could lead to a statement being printed twice when it only
  occurred once.

==== Version 3.4.10 - 30 October 2001 ====

- two bug fixes:
  - trace assertions were not working correctly, failing to
  reliably generate matches for all channels within the scope
  of an assertion. this was likely broken when statement merging
  was first introduced in version 3.3
  - added protection against the use of pids outside the valid
  range in remote references (i.e., less than 0 or over 255)

==== Version 3.4.11 - 17 December 2001 ====

- a bevy of small bug fixes:
- during verification, sorted send operations
  (e.g., q!!m) were not reversed accurately, leading to
  potentially inconsistent error trails
- 'else' was not interpreted correctly when it appeared
  as the first statement of a d_step
- process death was not in all possible cases considered a safe
  action, and thus could be deferred longer than necessary
- collapse did not in all cases generate the best compression

==== Version 3.4.12 - 18 December 2001 ====

- correcting a dumn coding error in 3.4.11 that made the
  pan.c source uncompilable..

==== Version 3.4.13 - 31 January 2002 ====

- new option -T, to suppress pid-dependent indenting of outputs
- new datatype 'pid' for storing return values from run expressions

- improved reporting of unreached states for models with inlines.
- improved reporting of memory use for bitstate verification runs.
- fewer unused vars in pan.c for common modes of compilation.
- during simulation each line of output is now immediately flushed
- new restrictions on the use of 'run': max 1 run operator per
  expression, and run cannot be combined with other conditionals.
  this secures that if a run expression fails, because the max nr
  of procs would be exceeded, the expression as a whole will have
  no side-effects.

- corrected bug in treatment of parameters to inlines
- corrected bug that showed up for some bizarre combinations
  of constructs (d_step nested in atomic, embedded in loop)
  sympton was that the spin parser would hang
- the maximum number of processes during simulation is now
  equal to that during verification (255) - to prevent
  runaway simulations.  the exact number can be redefined
  when spin is compiled, by adding a directive, e.g. -DMAXP=512
  similarly the max nr of message channels during simulation
  can be set by compiling spin with a directive, e.g. -DMAXQ=512
  the bounds used during verification (255) cannot be changed.

==== Version 3.4.14 - 6 April 2002 ====

- added new spin option -uN to truncate a simulation run after
  precisely N steps were taken.  in combination with option -jM
  this can select step M to N from a very long simulation
  (say guided or random);  example: spin -j10 -u20 spec
  prints step 10 up to 20, but nothing else

- corrected important bug introduced in 3.4.13 that caused a
  core dump during verification runs. the bug was caused by
  a poor attempt to correct reporting of unreached states
  due to statement merging effects.

- corrected compilation error for an unusual combination of
  compiler directives

==== Version 3.4.15 - 1 June 2002 ====

- much improved hashfunctions, at the suggestion of Jan Hajek
  from The Netherlands (the original implementor of the Approver
  tool from the seventies).
  this makes for better performance in both exhaustive searches
  (fewer hashcollisions on standard hashtable, therefore often
  faster), in bitstate and hashcompact searches (more coverage).
  the old hashfunctions are reenabled if pan.c is compiled
  with the new directive -DOHASH. the new functions are the default.
- improved reports of unreachable states, in the presence of
  statement merging.
- small change in the indenting of printf output -- it now lines
  up better with process columns in -c simulation output
- fewer compiler warnings
- some small fiddles with xspin to fix small problems
- giving up on maintaining the upgrade3 scripts -- they get too
  long and they do not seem to be used much

==== Version 3.4.16 - 2 June 2002 ====

- a bug slipped in in 3.4.15, bitstate verification failed
- also increased the default memory limit on PCs to 64 Mb

==== Version 3.4.17 - 19 September 2002 ====

- added a function printm(x) to print the symbolic name of
  an mtype constant.  this is equivalent to printf("%e", x),
  but can be more convenient.
- changed the structure of the never claim that is included
  by default if pan.c is compiled for non-progress cycle
  detection with directive -DNP
  the change is to check first for a move to the accepting
  state, rather than last.  this reduces the length of
  error trails that are generated, matching the earlier
  change made in version 3.2.2, thanks again to Dragan Bosnacki
  for pointing this out.
- rearranged the code for pan_ast.c so that it can be compiled
  separately, rather than as an include file of pangen5.c
- a bug had been hiding in the -DCOLLAPSE memory compression
  option that could in rare cases lead to states being missed
  during a verification
  the bug could be avoided with the optional -DJOINPROCS.
  it is now permanently fixed by extending the nr of bytes
  stored somewhat (the type of each process is now stored
  explicitly in the compressed statevector, to avoid the
  confusion that can result if two processes of the same
  contents but with different types could be created with
  the same pid, but as alternative options from the same
  state -- a case found by Remco van Engelen.
  the fix increases memory use slightly in some case (around
  10% in many test cases) but retains the greater part of
  the memory compression benefit. if needed, the fix can
  be disabled by compiling pan.c with -DNOFIX
- pan_ast.c is now a separately compiled file, just like
  all the others, instead of being #included into pangen5.c
- more attempts to fix the accuracy of reachability reports

==== Version 3.5.0 - 1 October 2002 ====

- variable names starting with an underscore were mistreated
  in the data flow analysis.
- this is meant to be a stable release of spin version 3, with
  minor changes in contact-information for the new spinroot.com
  website for all documentation, workshop information and
  newsletters.

==== Version 3.5.1 - 11 November 2002 ====

- bug in parsing of remote label references, could cause a
  core-dump of spin -a
- small additional improvements in reporting of unreachable
  states - to more accurately take into account optimizations
  made in the transition structure before verification starts
- noted incompatability of combining -DREACH and -DMA

==== Version 3.5.2 - 30 November 2002 ====

- slightly improved line number references in reporting syntax
  errors within d_steps
- extension: remote references usually are written as:
	proctypename[pid]@labelname
  if there is only one instantiation of the proctype, then the
  pid can more easily be figured out by Spin than by the user,
  so it can, in these cases, now be omitted, making an anonymous
  remote reference possible, as in:
	proctypename@labelname
  if there turn out to be multiple possible matches, Spin will
  warn in simulation mode -- but not in verification mode.
  (the additional check would probably be too consuming).
- during the execution of a d_step, spin would by default
  still print out every execution step in simulations (under
  the -p option).  now it will only do so in verbose mode
  (with also -v).
- if the last step in an atomic sequence was a rendezvous
  send operation, atomicity would not reliably move with
  the handshake to the receiver.  this is fixed.
- the simulator used a confused method to help the user out
  if the pid of a process was guessed incorrectly in a remote
  reference operation. this is now done more sanely:  if a
  variable is used for the pid, the simulator now trusts that
  it was set correctly -- the remote ref will simply fail with
  an error warning if this is not the case.  if the user specified
  the pid with a fixed constant, the simulator will now always
  add 1 to the number if the presence of a never claim is detected.
  (this is because behind the scenes the pid's will move up one
  slot to accomodate the claim -- this is always hidden from the
  user -- allowing the user to assume that pids always start at 0).

==== Version 3.5.3 - 8 December 2002 ====

- slightly better error reporting when the nr of pars in a send
  or run statement differs from the nr declared
- handling more cases of structure expansion (e.g., structure
  reference inside other structure used as msg parameter)

==== Version 4.0.0 - 1 January 2003 ====

- Summary of the main changes that motivated the increase of the
  main Spin version number from 3 to 4
- added support for embedded C code, primarily to support
  model extractors that can generate Spin models from C code
  more easily now, but indirectly this extension also makes
  all C data types and language elements available within
  Spin models.  a powerful extension - but with few safeguards
  against erroneous use. read the documentation carefully.
- added a Breadth-First search option (compile pan.c with -DBFS)
  this option works only for safety properties.  it often uses
  more memory and more time than the standard Depth-First search
  mode that Spin uses, but it can find the shortest possible
  error-trails more easily than with the dfs.
  cycle detection is hard with bfs, so it's not supported yet.
  all state compression modes are supported (bitstate, collapse,
  hash-compact, mininized automata, etc.)
- a small number of bug fixes -- e.g., some unless constructs
  gave compile-time errors in pan.c, some combinations of
  compiler directives gave compiler errors, fewer unused vars
  reported with some more rarely used combinations of compiler
  directives.
- slightly rearranged the makefiles -- there is now a separate
  shell script (make_pc) for windows and a makefile for unix
  (make_unix). there's also a script for compiling a debuggable
  version of spin with gcc and gdb (make_gcc).
  by default these scripts and makefiles now enable the LTL next
  operator.
- the call to sbrk() instead of malloc() on Unix is now no longer
  the default -- it could cause large amounts of memory that on
  Linux systems is pre-allocated to malloc, to be inaccessible.
- on Windows PC's the compiler directive -DPC to compile pan.c
  source is no longer needed (it is only needed to compiler spin
  itself)

All further updates will appear in the new file: V4.Updates