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

==== Version 6.0 - 5 December 2010 ====

The update history since 1989:

 Version 0: Jan. 1989 - Jan. 1990  5.6K lines: original book version
 Version 1: Jan. 1990 - Jan. 1995  7.9K lines: first version on netlib
 Version 2: Jan. 1995 - Aug. 1997  6.1K lines: partial-order reduction
 Version 3: Aug. 1997 - Jan. 2003 17.9K lines: bdd-like compression (MA)
 Version 4: Jan. 2003 - Oct. 2007 28.2K lines: embedded c-code, bfs
 Version 5: Oct. 2007 - Dec. 2010 32.8K lines: multi-core & swarm support
 Version 6: Dec. 2010 -           36.8K lines: inline ltl formula, parallel bfs
 Version 6.4.6:  2016 -           39.6K lines

==== Version 6.0.0 - 5 December 2010 ====

the main improvements in Spin version 6 are:

- support for inline specification of LTL properties:
        Instead of specifying a never claim, you can now
        specify LTL formulae directly inside a verification model.
        Any number of named LTL formulae can be listed and named.
        The formulae are converted by Spin into never claims in the background,
        and you can choose which property should be checked for any run
        using a new pan runtime parameter pan -N name.
        Example:
                    ltl p1 { []<>p  }
                    ltl p2 { <> (a > b) implies len(q) == 0 }

        There are a few additional points to note:
        -  Inline LTL properties state *positive* properties to prove, i.e.,
           they do not need to be negated to find counter-examples.
           (Spin performs the negation automatically in the conversions.)
        -  You can use any valid Promela syntax to specify the predicates
           (state properties). See, for instance, the use of expressions (a>b)
           and (len(q) == 0) in the examples above.
           So it is no longer needed to introduce macros for propositional symbols.
        -  White space is irrelevant -- you can insert newlines anywhere in an LTL block
           (i.e., in the part of the LTL formula between the curly braces).
        -  You can use textual alternatives to all temporal and some propositional operators.
           This includes the terms always, eventually, until, weakuntil,
           stronguntil, implies, equivalent, and release (the V operator),
           which are now keywords. So the first formula (p1) above could also be
           written as:
                         ltl p1 {
                                 always
                                        eventually p /* maybe some comment here */
                         }

- Improved scope rules:
        So far, there were only two levels of scope for variable
        declarations: global or proctype local.
        Version 6 adopts more traditional block scoping rules:
        for instance, a variable declared inside an inline definition or inside
        an atomic or non-atomic block now has scope that is limited to that inline or block.
        You can revert to the old scope rules by using spin -O (the capital letter Oh)

- New language constructs:
        There are two new language constructs, that can simplify the specification
        of common constructs: 'for' and 'select'. Both are implemented as meta-
        terms, which means that they are translated by the parser into existing
        language constructs (using 'do' or 'if').

        The new 'for' construct has three different uses:
                for (i : 1 .. 9) {
                   printf("i=%d\n", i)
                }
        simply prints the values from 1 through 9, meaning that the body of the
        for is repeated once for each value in the range specified.
                int a[10];
                for (i in a) {
                   printf("a[%d] = %d\n", i, a[i])
                }
        is a way to repeat an fragment of code once for each element in an array.
        In the example above, the printf will be executed once for each value from
        0 through 9 (note that this is different from the first example).
        This works for any array, independent of its type.
        The last use of the for is on channels.
                typedef utype { bin b; byte c; };
                chan c = [10] of { utype };
                utype x;
                for (x in c) {
                   printf("b=%d c=%d\n", x.b, x.c)
                }
        which retrieves each message in the channel and makes it available for the
        enclosed code. In this case, the channel (c above) must have been
        declared with a single parameter, the type of which must match the variable
        type specified in the for statement (the name before the 'in' keyword).
        [Note that with the introduction of the new keyword 'in' some early
        Spin models may now have syntax errors, if 'in' is used as a variable name.)

        The second new language statement is 'select' and its use is illustrated
        by this example:
                int i;
                select (i : 1..10);
                printf("%d\n", i);
        Select non-deterministically picks a value for i out of the range that
        is provided.

- Multiple never claims:
        Other than multiple and named inline LTL properties, you can also include
        multiple explicit (and named) never claims in a model. The name goes after
        the keyword 'never' and before the curly brace.
        As with inline LTL properties, the model checker will still only use one never
        claim to perform a verification run, but you can choose on the
        command line of pan which claim you want to use: pan -N name

- Synchronous product of claims:
        If multiple never claims are defined, you can use spin to
        generate a single claim which encodes the synchronous product
        of all never claims defined, using the new option: spin -e spec.pml
        (this should rarely be needed).

- Dot support:
        A new option for the executable pan supports the generation of
        the state tables in the format accepted by the dot tool from
        graphviz: pan -D
        The older ascii format remains available as pan -d.

- Standardized output:
        All filename / linenumber references are now in a new single standard
        format, given as filename:linenumber, which allows postprocessing
        tools to easily hotlink such references to the source.
        This feature is exploited by the new replacement for xspin, called ispin
        that will also be distributed soon.

Smaller changes:

- bugfix for line numbers being reported incorrectly in reachability reports
- all filename linenumber references unified as filename:linenr

==== Version 6.0.1 - 16 December 2010 ====

- fixed a bug in the implementation of the new 'for' and 'select' statements
  where the end of the range could be one larger than intended.
- extend the implementation of the new for and select meta-statements
  to allow expressions for the start and end value of the ranges
- when executing on Windowns without cygwin, better treatment of filenames
  with backslashes, avoiding that the backslash is interpreted as an
  escape in the pan.h source
- fix small problem in generation of pan.h, avoiding the string intialization
  ""-"" (when what is intended is "-"). remarkably, the C compiler does not
  complain about the first version and merrily subtracts the two addresses
  of the constant string "" and returns a 0...
- prevented the ltl conversion algorithm to run in verbose mode when spin -a
  is run with a -v flag (this produced a large amount of uninteresting output)
- also a couple of updates to the new iSpin GUI -- so that it works better
  on smaller screens, and also displays the automata view better (by adding
  option -o3 in the pan.c generation, so that all transitions are visible
  in the automata displayed.)

==== Version 6.1.0 - 4 May 2011 ====

- removed calls to tmpfile(), which seems to fail on some Windows 7 systems
- made it an error to have an 'else' statement combined with an i/o statement
  when xs or xr assertions are used to strengthen the partial order reduction.
  the 'else' would be equivalent to an 'empty()' call, which violates the
  xr/xs rules and could make the partial order reduction unsound
- avoid misinterpretation of U V an X characters when part of variable names
  used in the new style of inline specification of ltl formula
- improved treatment of remote references, under the new scope rules
- some support for an experimental new version of bfs, not yet enabled
- general code cleanup

==== Version 6.2.0 - 4 May 2012 ====

- added a new algorithm for parallel breadth-first search, with support for
  the verification of both safety and at least some liveness properties
  more detail is available at http://spinroot.com/spin/multicore/bfs.html

  the main new directive to enable parallel breadth-first search mode is
        -DBFS_PAR
  by default the storage mode that is used is hashcompact in a fixed size
  table (using open addressing).
  by default verification will continue as long as possible, but it can be
  forced to stop when the table is filled to capacity by defining
        -DSTOP_ON_FULL
  storage can be changed from hashcompact to full statevector storage with
        -DNO_HC
  (although this is not really recommended)
  you can also use bitstate hashing instead, by compiling with
        -DBITSTATE
  and (independently) you can use diskstorage to save some memory, with
        -DBFS_DISK
  but this has the disadvantage of making the verifier run slower, defeating
  much of the benefit of the parallel search algorithm.
  the default maximum length of a cycle for liveness violations is set to 10
  steps; this can be changed by defining
        -DL_BOUND=N
  (which is safe, but should rarely be necessary -- setting it too large
  reduces the accuracy of the search (see the spin2012 paper)).

  when no compare and swap function __sync_bool_compare_and_swap is predefined
  (e.g. cygwin when compiling with gcc) you can define:
        -DNO_CAS

  the new -DBFS_PAR mode cannot be combined with -DBCS, -DNP, or -DMA

- some new language features to support modeling priority-based embedded software
  (more detail on this at http://spinroot.com/spin/multicore/priority.html)

  a new predefined local variable in proctypes:
        _priority          holds the current priority of the executing process
  two new predefined functions:
        get_priority(p)    returns the priority of process p (p can be an expression)
        set_priority(p, c) sets priority of process p to c (p and c can be expressions)

  the use of these priority features cannot be combined with rendezvous statements
  and it requires compilation with -DNOREDUCE

  when process priorities are used (and the new mode is not disabled with -o6
  see below) then only the highest priority enabled process can run
  process priorities must be in the range 1..255

- inlines can now contain a return statement, but it can be used only in a
  few simple cases to return a single integer value
  using this feature a single inline call can now be used on the right-hand side
  of a simple assignment statement, for example
        x = f(a,b);             # works
  but not in other contexts where one would normally expect a value to be returned,
  like an expression) e.g., these cases do not work:
        if :: (a > fct()) ->    # does not work
        if :: (fct()) ->        # does not work
        x = f(a,b) + g(x)       # does not work
  the return statement, being so restricted is of limited use, may therefore
  disappear again in future versions

- a label name can now appear also without a statement following it
  (useful, for instance, to place a label at the end of the proctype or
  sequence without having to add a dummy skip statement)

- and else statement can now appear as the only option in an if or do
  and then evaluates to 'true' -- this can be useful in some cases with
  machine generated models

- new spin options
  spin option -o6 reverts to the old (pre 6.2.0) rules for interpreting
  priority annotations
  there's also a new experimental option -pp to improve the formatting of
  a badly formatted spin model (e.g. machine generated).  it is far from perfect
  and the option may therefore disappear again in some future version

- restructed how pan.h is generated, to make sure that it does not declare any
  objects, only prototypes, datatypes, and structures -- this makes it possible
  to include pan.h safely in other files as well

- also made separate compilation of claims and code work again (if you don't know
  what this means, it's best that you don't learn it either...  it's an obscure
  feature that almost nobody uses)

- in bitstate mode the default size of the bitarray is now 16 MB (-w27), was 1MB (-w23)

- in standard mode the default hashtable size is now -w24 (up from -w19)

- bug fixes
  the clang analyzer noted that the code in dstep.c left a local array buf
  accessible via a global pointer (NextLab) also after the function returned.
  corrected by declaring the local array as a static structure
  similarly, removed some dead assignments in mesg.c flagged by clang.

- cleaned up the scope rule enforcement a bit, so that top level local variable
  declarations do not get any prefix -- simplifying the remote referencing
  only declarations in inner-blocks or inlines are now affected, and get a scope
  unique prefix (which is hidden from the user level in almost all cases)

- corrected a problem noted on the spinroot forum that one could not use a
  break statement inside the new 'for' construct (correction in spin.y and flow.c)
  problem was that the break target was not defined early enough in the parsing

- corrected a problem where label names were affected by the new scope rules,
  causing some confusion with remote references and jumps

- made the format of spin warning messages more consistent throughout the code

- better recognition of invalid transition references in guided simulation
  (scenario replay) in guided.c

- statement merging is now disabled when proctype 'provided' clauses are used

- corrected problem when an conditional expression was used in an argument to an inline

- corrected problem when a remote reference was used as an array index inside an inline ltl formula

- corrected the makefile to allow the use of multiple cores for parallel compilation
  (using, for instance, "make -j 8")

- now preventing assignments to the predefined local variable _pid (...)

- fixed treatment of <-> or "equivalent" in ltl formula -- it wasn't always recognized correctly

- some more general code cleanup

==== Version 6.2.1 - 14 May 2012 ====

- first bug in 6.2: the new 'select' statement was broken and triggered a
  syntax error 'misplaced break statement' -- fixed

==== Version 6.2.2 - 6 June 2012 ====

- fixed bug in handling of the new 'set_priority' call. priorities were not
  properly restored during the depth-first search, which could lead to
  strange verification results.
- fixed a bug that prevented use of parallel bfs in combination with collapse
  compression. the combination isn't really recommended, but at least it
  shouldn't crash of course... (the recommended mode for parallel bfs is
  the default storage mode, which ias based on hashcompact, or bitstate).
- added missing "extern YYSTYPE yylval;" in reprosrc.c, which prevented
  compilation in some platforms
- added warning against the use of hidden variables when using bfs
- excluded run statements from statement merging, to secure correctness
  when priority tags are used
- omitted the message type field in datapackets exchanged with other cores
  in parallel bfs mode, in those modes where the type field can be deduced
  from other parts of the data, to reduce memory needed for the bfs queues

==== Version 6.2.3 - 24 October 2012 ====

- fixed bug when using BFS_DISK in combination with BFS_PAR
- fixed a bug when using process priorities, added initialization for the
  priority to make sure it is set when a priority is not explicitly defined
- fixed code when using COLLAPSE in combination with BFS_PAR
- added warning when replaying an error-trail for a model with embedded c-code,
  to make sure the user knows that the c-code fragments are not executed.
  to replay an error-trail for models with embedded c-code only the compiled
  pan.c file can be used (e.g., by executing ./pan -C)
- no longer pointing to /lib/cpp for preprocessing, which dates to early
  unix system; the default is to use gcc, or plain cpp
- renamed global vars j2, j3 and j4 in pan.c to j2_spin, j3_spin and j4_spin
  to avoid potential name clashes with embedded c-code fragments in models
- added hints in bfs parallel mode at end of runs if the hash-table could
  be resized in a new run, to improve performance
- small additional speedups in BFS_PAR mode (finetuning the wait discipline
  when switching from one generation of states to the next)
- changed the default max nr of cores in BFS_PAR mode from 32 to 64
- better memory alignment in BFS_PAR mode
- other small fixes and minor code cleanup

==== Version 6.2.4 - 10 March 2013 ====

- never claims generated from inline ltl formula are now automatically
  added when replaying an error trial (so it will no longer say 'claim
  ignored' in those cases)
- improved treatment of the STDIN channel on linux systems
- changed the format of never claims to improve error-trails
  (by using an assertion in some cases instead of a goto to
   the end of the claim -- this also includes changing 'if' into 'do'
   in some cases, which may affect postprocessors that rely on the
   older format)
- changed parser to allow constant expressions in more places where
  earlier only numeric constants were accepted (e.g., for active [...]
  specifying the size of a channel, and the size of an array)
- small improvements in memory use for parallel bfs mode (BFS_PAR)
- added a BFS_NOTRAIL mode for parallel bfs, reducing memory use if
  no counter-example error trail is expected
- fixed bug in the evaluation of 'enabled(pid)' during verifications
- fixed bug in implementation of weak-fairness algorithm, which could
  in rare causes cause a fair cycle to go unreported.
- improved calculation of hash-factor for very large bitstate spaces
- fix bug introduced in 6.2.3 that gave a compiler error for -DBITSTATE
- other minor code cleanup

==== Version 6.2.5 - 4 May 2013 ====

- fixed bug when priorities are used and statement merging is enabled
  (the default) -- this could cause state updates to get out of sync,
  leading to a possible crash of the verifier.
- added the keyword "const" to many of the constant array declarations,
  to reassure static analyzers that printfs would not alter the contents
  of these arrays
- fixed bug in verifier in handling of priority based scheduling, which
  could lead it to erroneously get process ids wrong; fixed problems
  with the use of priorities when used in combination with ltl properties
  or never claims; fixed a bug that could lead to a crash due to not
  correctly storing backup values for priorities that are modified
  dynamically with 'set_priority()' calls
- more small changes to appease static source code analyzers
- increased various buffer sizes to allow the parsing of larger ltl formula

==== Version 6.2.6 - 17 February 2014 ====

- corrected bug in treatment of break statements hiding in unless constructs
- corrected treatment of priorities (example by Mirtha Line Fernandez Venero)
- added some new predefined routines to simplify integration with modex:
  spin_malloc, spin_join, spin_mutex_free, spin_mutex_lock, spin_mutex_unlock,
  and spn_mutex_init (not all of these may survive future updates)
- added a new spin option -x to directly print the transition table for a model
  (the option parses the model, generates pan.c, compiles it, and then
   runs it with option -d)
- ONE_L is now defined as 1L instead of (unsigned long) 1 to avoid a double
  expansion of unsigned long to unsigned long long caused by a macro used
  for compilation for 64-bit windows systems
- mildly improved error reporting
- doubled the size of the yacc parse stack (YYMAXSTACK), to support
  parsing larger models

==== Version 6.2.7 - 2 March 2014 ====

- another fix of enforcement of priorities during verification
- fixed a bug in treatment of -DT_RAND and -DP_RAND that could
  lead to the analyzer hanging in some cases

==== Version 6.3.0 - 4 May 2014 ====

- A new minor version number because the Promela syntax rules changed.
  A semi-colon at the end of the line is now optional.
  this is implemented by having the lexical analyzer insert the
  semi-colons automatically if they are missing.
  Almost all models will still parse correctly, but the change can in
  a few cases cause older models to trigger a syntax error if a
  statement seperator is assumed in an unsuspected place, e.g., in the
  middle of a multi-line expression. Avoid it by making sure a
  multi-line boolean expression is always enclosed in round braces,
  or by having the last token on a line be an operator.
  For instance, these expressions will parse correctly:
        if
        :: (a
           && b) -> ...
        :: a &&
            b -> ...
        fi
  but these do not:
        if
        :: (a)    // parser cannot see that the expression is incomplete
           && (b) -> ...
        :: a      // same here
           && b -> ...
        fi
  To revert to the old syntax rules, use spin option -o7

- added 5 new options:
        -run    compile and run, verify safety properties
  # Note the next four have been replaced in later versions, see 6.4.0
        -runA   compile and run, find acceptance cycles
        -runAF  compile and run, find weakly-fair acceptance cycles
        -runNP  compile and run, find non-progress cycles
        -runNPF compile and run, find weakly-fair non-progress cycles
  for instance:
        spin -runA leader.pml

- spin option -M changed:
  replaced ps_msc.c with msc_tcl.c and with it changed the spin -M
  option from generating scenarios in Postscript to generating them
  as TclTk output. the new version of iSpin makes use of this as well.
  By default the maximum length of the scenario generated is 1024
  (equivalent to an option -u1024). To change it to a different
  value, use the -u option (e.g., spin -u2048 -M leader.pml).

- when using randomized searches (T_RAND, P_RAND, or RANDOMIZE, or pan_rand())
  the seed for the random number generator now also depends on the choice of -h
  (i.e., the seed will change if you change the hashfunction used with ./pan -h)

- added more support for verification of models extracted by Modex from
  C code with pthread library calls embedded.

- simplified the directory structure of the distribution somewhat by
  combining all examples Spin models in a single directory Examples,
  with subdirectories for specific subsets: LTL, Exercises, Book_1991
  (the old subdirectories Samples, Test, and iSpin/ltl_examples are now gone)

- bug fixes:
  - another bug fix in treatment of priorities in verification runs
    the priority tag in active proctype declarations was erroneously ignored
  - fixed the accuracy of reporting the cycle-point in liveness errors
    discovered in a breadth-first search with the piggyback algorithm
    (courtesy Ioannis Filippidis, 4/2014)
  - restored original settings for the piggyback algorithm, which restored
    much of the cycle finding capabilities that were lost after version 6.2.2
  - improved parser so that it can continue after the first syntax error
  - improved accuracy of line numbers in traces (courtesy Akira Tanaka, 3/2014)
  - prevented some compilation errors for unusual combinations of directives
  - removed some warnings for printf statements with the wrong qualifiers
    (e.g., %d for a long int, which should be %ld, etc.)

==== Version 6.3.1 - 11 May 2014 ====

- big improvement in the handling of the new -run parameter to Spin
  that will make it much easier to work with Spin.
  all new functionality is now supported by the -run parameter alone,
  so these four experimental options from 6.3.0 are no longer needed:
        -runA,-runAF, -runNP, -runNPF
  in the new setup, a -run parameter can be followed by any additional
  settings and options that should be passed to either the compiler
  (for compiling pan.c) or the ./pan verifier itself as runtime options.
  the rule is that all parameters that preceed a -run argument are
  interpreted by Spin itself for parsing the model; all parameters that
  follow a -run parameter are passed down to compiler or verifier
  for instance, to get the equivalent of -runNPF from 6.3.0, you can
  now say:
        spin -run -DNP -l -f spec.pml
  to get an immediate run searching for weakly fair non-progress cycles
  similarly, to optimize the compilation and reduce the run to a depth
  of 3000 step, you would say:
        spin -run -O2 -DNP -l -f -m3000 spec.pml
  with this new setup you should in principle never have to compile
  the pan.c source files manually, or invoke the verification manually.
  if you want to redefine a macro used in the Spin model itself, you
  can still pass that new definition directly to spin, by placing it
  before the -run parameter, for instance:
        spin -DMAX=24 -run -O2 -DNP -l -f -m3000 spec.pml
  (assuming that macro MAX is used inside spec.pml)

- new exercises and tutorials to match these changes in
        http://spinroot.com/spin/Man/1_Exercises.html
        http://spinroot.com/spin/Man/3_SpinGUI.html
        http://spinroot.com/spin/Man/4_SpinVerification.html

- bug fixes:
  - in simulations, dynamically changing process priorities did not always
    work correctly. now fixed
  - additional corrections to the line number reporting in simulations

==== Version 6.3.2 - 17 May 2014 ====

- this update makes all new spin options work correctly,
  and can be compiled cleanly, on Linux, Windows PCs, and
  Mac's, and it supports all new Modex options for direct
  verification of C source code (http://spinroot.com/modex)

- other updates and fixes:
  - assigning to the reserved predefined variables (_last,
    _p, _pid, _nr_qs, _nr_pr) is now intercepted correctly
  - assigning to _priority now works correctly also in simulations

- new features:
  - you can now initialize an array of integers with a list
    in proctypes, and in global declarations (but not yet
    if the array is declared inside an inline definition)
    for instance:  int a[4] = { 3, 1, 4, 1 }
    all initialization values must be constants
  - parser improved so that it can allow the use of variables
    or channels named 'in' -- without causing a conflict with
    the token 'in' from for-statements
  - process priorities now work in simulation the same as in
    verification -- you can revert to the old behavior with -o7

- for this version added a Mac executable to the distribution
  (no guarantees that future versions will also have this though)

==== Version 6.4.0 - 19 September 2014 ====

- main new features:

  - new ./pan runtime option flag -hash to randomly generate a hash polynomial,
    for instance to separate multiple runs with bitstate hashing better.
    the seed for the random number generator determines what polynomial
    is going to be generated (same seed means same polynomial). the seed
    can be changed with ./pan option -RSn where n is any positive integer
    e.g., obtained from a Unix/Linux system call 'rand.'
    for instance ./pan -RS`rand` -hash   # using backquotes around rand

  - extended the number of features that is supported in combination with
    the  new spin runtime options that were introduced in 6.3.0
    four main types of spin (not pan) options are now supported:

        spin [..options1..] -run      [..options2..] modelname.pml
        spin [..options1..] -replay   [..options2..] modelname.pml
        spin [..options1..] -biterate [..options2..] modelname.pml
        spin [..options1..] -swarmN,M [..options2..] modelname.pml

    other parse-time (options1) or runtime (options2) options can be
    passed along as shown above, and as explained below:

    o parse-time options are placed *before* the mode flag (-run, -replay, etc.)

    o compile-time and run-time options are placed *after* the mode flag.
        this can include compiler directives to be used to compile pan.c
        (which happens in the background), or to execute the resulting ./pan
        executable (which now also happens automatically).

    note 1: when you use this command:
           spin -DX=2 -m -run -DSAFETY -m100 modelname
        compiler directive -DX=2 is used in the preprocessing of the model, and
        compiler directive -DSAFETY is used to compile the resulting pan.c.
        and further, the first -m argument is interpreted by spin, and the
        second -m100 argument is interpreted by ./pan

    note 2: the new options make use of gcc, which is assumed to be
        installed on your system, so on Windows systems this is unlikely
        to work unless you also have cygwin with gcc installed.  you can
        change the compiler to be used by compiling the spin sources with
        a different choice for -DCPP (e.g., "-DCPP=clang -E -x c" might work)
        when using the new options on a Windows system with gcc may also
        doom you to 32-bit pan executables, which will limit the size of
        memory you can allocate for a search to 2GB. using linux is recommended.

    explanation of the use of the spin -replay option:
        this option can be used to replay an existing error trail-file
        (e.g., found with an earlier spin -run)
        if the model contains embedded c-code, the ./pan executable is used
        for the replay; otherwise spin itself is used for the replay.
        note that ./pan recognizes different runtime options than spin itself
        so it can matter which of these two cases applies for [..options2..]
        you can of course always still fall back on the old
           spin -t -p modelname.pml
        method for models withnout embedded C code, or the ./pan -r method for
        models with embedded C code.

    explanation of the use of the spin -run option:
        a synonym of this option is -search -- it behaves identical to -run.
        this option is used to generate a verifier (pan.c), compile it, and
        execute it run, all without further user intervention.
        new options that can be used in the [..options2..] part include:
          -bfs          to perform a breadth-first search
          -bfspar       to perform a parallel breadth-first search
          -bcs          to use the bounded-context-switching algorithm
          -bitstate     or -bit, to use bitstate storage
          -link file.c  to link the pan.c to file.c in the compilation
          -collapse     to use collapse state compression
          -hc           to use hashcompact storage
          -noclaim      to ignore all ltl and never claims
          -p_permute    to use process scheduling order permutation
          -p_rotateN    to use process scheduling order rotation by N (default 0)
          -p_reverse    to use process scheduling order reversal
          -ltl p        to verify the ltl property named p
          -safety       to compile for safety properties only (default is liveness+safety)
          -i            to use the dfs iterative shortening algorithm
          -a            to search for acceptance cycles (and compile correspondingly)
          -l            to search for non-progress cycles (and compile correspondingly)

    explanation of the use of the new spin -biterate option:
          uses bitstate compilation plus iterative search refinement for the
          execution of ./pan with hashtable size increasing step by step
          from -w18 upto -w35 -- until an error is found.
          this performs 18 runs sequentially, with the first runs executing
          very fast -- thus making it likely that errors are found very quickly
          each new run increases precision and runtime, until the max is reached

    explanation of the use of the new spin -swarmN,M option:
          the most advanced new search mode -- only for use on larger multi-core
          systems (e.g., 16 cores and up).
          this option performs N runs in parallel and increments -w every M runs
          for each run performed several other parameters are also randomized
          (e.g., the hash function used, process scheduling decisions, transition
           ordering, etc. similar to what the swarm preprocessor would do)

          the default value for N is 10, and the default for M is 1

          the swarm option makes use of a new compiler directive for pan.c files
          called -DPERMUTED that allows for more extensive options for process
          scheduling randomization (p_rotate, p_reverse, and p_permute, see below)

          spin -swarmN,M will use the following compilation directives and
          runtime parameters (most of this is meant to be internal to Spin,
          but listed here for completeness as background information).
          (the new options below are probably not too useful when used separately)
    
          swarm compilation adds:
             -DBITSTATE -DPUTPID and -DPERMUTED (a new directive, see below)
             -DSAFETY   unless there is also -a or -l parameter in [..options2..]
             -DNOFAIR   unless there is a -f parameter or there is no -a or -l

          runtime flags used (with randomized arguments):
             -w18       unless there already is a -w argument, then use that as starting point
             -i_reverse envoked on some of the runs, to change initialization orders of processes
             -t_reverse envoked on some of the runs, to reverse transition orders
                        unless -DT_RAND or -DT_REVERSE are defined
             -h0        unless there already is a -hN argument, then use that as starting point
                        or if the user specified -hash, then do not use -h
             -k1        unless there already is a -k argument, then use that as starting point
             -p_rotate0 unless there already is a different -p_rotateN argument,
                        unless there is a -p_permute argument, then do not use
             -RSn       using internal choice for n, overrides a user-defined argument
             -a         unless there is already a -a or -l argument
                        or there is a -DNOCLAIM directive
                        or there are no accept-state labels in the model or ltl formula
      
          the swarm option varies these parameters across all parallel runs:
             -w         every Nth iteration (from -swarmN,M):  18..35
             -h         every run 0..499  (unless the user defined -hash)
             -p_rotate  every run 0..255 (unless suppressed by p_normal or p_reverse)
             -k         every run 1..3
             -T         every run 0..1
             -P         every run 0..3
             -RSn       every run
             -p_reverse is enabled on every 5th run, but overriden by -P0/1
                        in half the cases (overrides p_rotate if selected)
             -p_normal  to revert to normal process scheduling at least once ever 6 runs

    the new -DPERMUTED directive enables a set of new runtime options to pan
    that support how the process scheduling selecting can be modified during the search:

        -p_permute  -- to randomly permute the processes (the default)
        -p_rotate   -- to rotate the process ready queue 1 slot
        -p_rotateN  -- to rotate the process ready queue N slots
                       (using -p_rotate0 will have no effect of course)
        -p_reverse  -- to reverse order for all processes
        -p_normal   -- perform process scheduling as if -DPERMUTED was not defined

    if more than one of these options is used, the last one wins.
    if -DPERMUTED is defined and none of these flags are used
    the default process scheduling order is -p_permute
    note that using -DPERMUTED adds overhead and slows down a search, which is only
    reasonable when used in combination with the swarm randomizations

- two additional pan runtime options were added that can affect process
  scheduling and transition selection orders:
        -i_reverse -- reverse the initialization order of all processes declared 'active'
        -t_reverse -- reverse the order of transition selections

- other smaller additions:
  - extended the number of builtin hash-polynomials (selected via -hN) from 32 to 100
  - can now place ltl formula anywhere in a Promela file -- it does not need
    to appear after all symbols that are referenced in the formula have been
    declared (the parser will now always defer processing until the entire
    specification has been parsed)
  - added a quick sanity check to parsing of ltl formula, to catch some common mistakes.

- some fixes:
  - removed some false warnings about duplicate label declarations
  - added -std=gnu99 to calls to the gcc compiler an preprocessor
    to make sure that // comments in Promela specifications are recognized
  - removed pc_zpp.c -- the builtin preprocessor used when compiled with -DPC
    the original reason for adding this was to avoid a command window
    from flashing on the screen when an external preprocessor was
    called from within xspin. that problem no longer seems to exist, and
    so this restricted version of the preprocessor is no longer needed
  - small improvements in typechecking in receive statements
  - improved the look of message sequence charts generated with spin -M
  - fewer compiler warnings when using models with priorities
  - deprecated flag ./pan -s now removed (sam as ./pan -k1)
  - fixed bug in implementation of bounded context switching code (-DBCS)
    that could cause states to be restored incorrectly
  - removed the mapping of type long to long long on windows pcs (-DPC)
  - improved parsing for very large models, saving about 20% of cpu-time,
    by switching from unsorted to sorted linked lists in a few places
  - a few more bug fixes in the implementation of support for dynamically
    changing priorities
  - fixed a bug in replay of error trails for ltl formula, for models where
    multiple formula are used, to make sure that the formula are parsed
    in the same way for verification and for replay.

- new or renamed compilation directives
  - -DREVERSE (gone) to reverse process selection order is renamed to
    -DP_REVERSE to make it more symmetric with the older
    -DT_REVERSE used to reverse the transition selection order
  - the new directive -DPERMUTED overrides -DP_REVERSE if both are used

==== Version 6.4.1 - 5 October 2014 ====

- two small fixes to 6.4.0
  - the new -run -biterate options wasn't working correctly

  - on windows32 and windows64 versions, suppressed logos from gcc
    and improved method for detecting whether gcc.exe is a symbolic
    link or not

==== Version 6.4.2 - 8 October 2014 ====

- restored the correct behavior for a standalone -run argument
  (i.e., without -swarm or -biterate), which should perform a single
  compilation and execution of the ./pan verifier
- less chatter on stdout for executed background commands
  (you can restore this by adding -v or -w -- if you use -w the
  commands generated for -biterate or -swarm are shown, but not
  executed)

==== Version 6.4.3 - 16 December 2014 ====

- added definition of tas() function for powerpc64, courtesy of srirajpaul (Rice CAF group)
- corrected parsing unsigned int variables in c_state declarations
- allow use of a variable name in an array bound, provided that variable
  is an initialized scalar - generats a warning when this is used
- made sure ltl formula are parsed the same way on replay of an error
  trail as when generating a verifier
- improved matching of labels if the same labelname is used in multiple scopes
  (e.g., different inlines)
- fewer issues with WindowsPC compiled versions
- the label "accept_all" in neverclaims is no longer treated as an indication
  of a check that requires cycle detection
- presence of -bfs will now preclude addition of -a flag in auto-generated runs
- fixed limit that was set too short when reproducing an MSC from an error-trail
  with spin option -M
- small improvement in replays of error-trails with ./pan -r
- improved support for Modex generated models
- now handles select statements in preprocessor (spinlex.c) rather than in the
  grammar -- replaces it with a true non-deterministic choice for relatively
  small ranges (1..32 entries), rather than a non-deterministically terminated
  do-loop, for simpler error trails
- fixed some minor type inaccuracies

==== Version 6.4.4 - 1 November 2015 ====

- when compiletime option -DNP is defined after a -run flag, the runtime
  option -l is now added, if missing.
- removed the dummy definition of yywrap()
- added make32 for 32-bit linux builds (make -f make32)
- improved printing of mtype values in trace replay with pan
- improved support for cond_wait, cond_signal, and mutex_init
  for models extracted by modex (not meant to be called directly)
- improved replay of error traces when -DPERMUTED is used
- improved verbose output for -DPERMUTED options
- added 64-bit murmurhash function as an alternative on 64-bit systems
  it is enabled by compiling pan.c with an additional -DMURMUR directive
- replaced call srandom() with srand() and replaced random() with rand()
- added p_randrot to the set of options supported by -DPERMUTED for
  rotating the process scheduling list by a random amount (see 6.4.0)
- added a runtime option (for pan.c) called -rhash to generated a
  random hash-polynomial for the run (as determined by the seed for the
  random number generator, which can be changed with runtime option -RSnnn)
  if no seed is selected with -RS, then time is used to seed the random
  number generator. Compile pan.c with -DRHASH to enable this option.
  If -DRHASH is defined it will also enable directive -DPERMUTED.
  see VMCAI2016 paper for examples of its use in cloud / swarm verification.
- removed the warning "this search is more efficient if compiled with -DSAFETY"
- improved spin replay of error-traces for models using process priorities
  together with ltl properties or never claims
- added support for using c_expr inside ltl formula
- made select ( name : constant .. constant-expression ) work again,
  e.g. so that you can again say:  select (i : 0 .. N-1)
- other minor fixes and improvements throughout

==== Version 6.4.5 - 1 January 2016 ====

- The first version of Spin that is released under a standard
  BSD 3-Clause open source license. This was possible thanks to
  the transfer of the copyright on all Spin sources from
  Alcatel-Lucent (the successor to AT&T in ownership of Bell Labs),
  to me on 30 December 2015. This release also comes 25 years
  after the very first source release of Version 1.0 in Jan. 1991.
  Since the license is now standard, and no longer Lucent specific,
  the Spin sources and executables are now more easily packaged
  for distribution in other open source systems, e.g., Ubuntu.

- other minor updates, e.g. to remove a sanity check that caused
  inline ltl formulae like ltl { true U (true U true) } to
  be flagged as incorrect, and the correction of an incorrectly
  bracketed expression in function spin_cond_wait, which is
  used by the modex model extractor.

==== Version 6.4.6 - 2 December 2016 ====

- fixed bug in treatment of select() statement, when used inside
  and inline definition.
- made it an error to use 'run' to initialize a variable inside
  a declaration.
- small fixes in d_step.c, run.c, pangen2,c, and main.c (missing
  parentheses around subexpressions with a binary operators).
- small improvements in the makefile
- fix in mesg.c to allow recv poll operators on rhs of
  assignments (erroneously flagged before as a side-effect)
- prefixed some more generated variables in pan.c to
  avoid name-clashes (_nstates, _endstateN, _startN)
- prevented possible compiler warnings on definition of
  a recently added function spin_join()
- added new function mutex_destroy to support modex
  conversions from C to Promela
- fixed typo in BFS_PAR print statement (Seperate->Separate)
- fixed flaw in generation of BFS_PAR code, preventing
  compiler warnings
- made hash function inside sym.c return an unsigned int
