Perl executable. It is far from complete and probably contains many errors.
Please refer any questions or comments to the author below.
+=head1 Variables
+
=head2 Datatypes
Perl has three typedefs that handle Perl's three main data types:
call the function C<sv_grow>. Note that C<SvGROW> can only increase, not
decrease, the allocated memory of an SV and that it does not automatically
add a byte for the a trailing NUL (perl's own string functions typically do
-SvGROW(sv, len + 1)).
+C<SvGROW(sv, len + 1)>).
If you have an SV and want to know what kind of data Perl thinks is stored
in it, you can use the following macros to check the type of SV you have.
line and all will be well.
To free an SV that you've created, call C<SvREFCNT_dec(SV*)>. Normally this
-call is not necessary (see the section on L<Mortality>).
+call is not necessary (see the section on L<Reference Counts and Mortality>).
=head2 What's Really Stored in an SV?
This returns NULL if the variable does not exist.
-The hash algorithm is defined in the PERL_HASH(hash, key, klen) macro:
+The hash algorithm is defined in the C<PERL_HASH(hash, key, klen)> macro:
i = klen;
hash = 0;
while (i--)
hash = hash * 33 + *s++;
+=head2 Hash API Extensions
+
+Beginning with version 5.004, the following functions are also supported:
+
+ HE* hv_fetch_ent (HV* tb, SV* key, I32 lval, U32 hash);
+ HE* hv_store_ent (HV* tb, SV* key, SV* val, U32 hash);
+
+ bool hv_exists_ent (HV* tb, SV* key, U32 hash);
+ SV* hv_delete_ent (HV* tb, SV* key, I32 flags, U32 hash);
+
+ SV* hv_iterkeysv (HE* entry);
+
+Note that these functions take C<SV*> keys, which simplifies writing
+of extension code that deals with hash structures. These functions
+also allow passing of C<SV*> keys to C<tie> functions without forcing
+you to stringify the keys (unlike the previous set of functions).
+
+They also return and accept whole hash entries (C<HE*>), making their
+use more efficient (since the hash number for a particular string
+doesn't have to be recomputed every time). See L<API LISTING> later in
+this document for detailed descriptions.
+
+The following macros must always be used to access the contents of hash
+entries. Note that the arguments to these macros must be simple
+variables, since they may get evaluated more than once. See
+L<API LISTING> later in this document for detailed descriptions of these
+macros.
+
+ HePV(HE* he, STRLEN len)
+ HeVAL(HE* he)
+ HeHASH(HE* he)
+ HeSVKEY(HE* he)
+ HeSVKEY_force(HE* he)
+ HeSVKEY_set(HE* he, SV* sv)
+
+These two lower level macros are defined, but must only be used when
+dealing with keys that are not C<SV*>s:
+
+ HeKEY(HE* he)
+ HeKLEN(HE* he)
+
+
=head2 References
References are a special type of scalar that point to other data types
SV* sv_bless(SV* sv, HV* stash);
The C<sv> argument must be a reference. The C<stash> argument specifies
-which class the reference will belong to. See the section on L<Stashes>
-for information on converting class names into stashes.
+which class the reference will belong to. See the section on
+L<Stashes and Globs> for information on converting class names into stashes.
/* Still under construction */
Upgrades rv to reference if not already one. Creates new SV for rv to
-point to.
-If classname is non-null, the SV is blessed into the specified class.
-SV is returned.
+point to. If C<classname> is non-null, the SV is blessed into the specified
+class. SV is returned.
SV* newSVrv(SV* rv, char* classname);
-Copies integer or double into an SV whose reference is rv. SV is blessed
-if classname is non-null.
+Copies integer or double into an SV whose reference is C<rv>. SV is blessed
+if C<classname> is non-null.
SV* sv_setref_iv(SV* rv, char* classname, IV iv);
SV* sv_setref_nv(SV* rv, char* classname, NV iv);
Copies the pointer value (I<the address, not the string!>) into an SV whose
-reference is rv. SV is blessed if classname is non-null.
+reference is rv. SV is blessed if C<classname> is non-null.
SV* sv_setref_pv(SV* rv, char* classname, PV iv);
-Copies string into an SV whose reference is rv.
-Set length to 0 to let Perl calculate the string length.
-SV is blessed if classname is non-null.
+Copies string into an SV whose reference is C<rv>. Set length to 0 to let
+Perl calculate the string length. SV is blessed if C<classname> is non-null.
SV* sv_setref_pvn(SV* rv, char* classname, PV iv, int length);
terminates. This is a memory leak.
The correct procedure, then, is to use C<newRV_noinc> instead of
-C<newRV_inc>. Then, if and when the last reference is destroyed, the
-reference count of the SV will go to zero and it will be destroyed,
+C<newRV_inc>. Then, if and when the last reference is destroyed,
+the reference count of the SV will go to zero and it will be destroyed,
stopping any memory leak.
There are some convenience functions available that can help with the
SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
third creates a mortal copy of an existing SV.
-The mortal routines are not just for SV's -- AV's and HV's can be made
-mortal by passing their addresses (type-casted to C<SV*>) to the
+The mortal routines are not just for SV's -- AV's and HV's can be
+made mortal by passing their address (type-casted to C<SV*>) to the
C<sv_2mortal> or C<sv_mortalcopy> routines.
=head2 Stashes and Globs
-A stash is a hash table (associative array) that contains all of the
-different objects that are contained within a package. Each key of the
-stash is a symbol name (shared by all the different types of objects
-that have the same name), and each value in the hash table is called a
-GV (for Glob Value). This GV in turn contains references to the various
-objects of that name, including (but not limited to) the following:
+A "stash" is a hash that contains all of the different objects that
+are contained within a package. Each key of the stash is a symbol
+name (shared by all the different types of objects that have the same
+name), and each value in the hash table is a GV (Glob Value). This GV
+in turn contains references to the various objects of that name,
+including (but not limited to) the following:
Scalar Value
Array Value
For more information on references and blessings, consult L<perlref>.
-=head2 Magic
+=head2 Double-Typed SV's
+
+Scalar variables normally contain only one type of value, an integer,
+double, pointer, or reference. Perl will automatically convert the
+actual scalar data from the stored type into the requested type.
+
+Some scalar variables contain more than one type of scalar data. For
+example, the variable C<$!> contains either the numeric value of C<errno>
+or its string equivalent from either C<strerror> or C<sys_errlist[]>.
+
+To force multiple data values into an SV, you must do two things: use the
+C<sv_set*v> routines to add the additional scalar type, then set a flag
+so that Perl will believe it contains more than one type of data. The
+four macros to set the flags are:
+
+ SvIOK_on
+ SvNOK_on
+ SvPOK_on
+ SvROK_on
+
+The particular macro you must use depends on which C<sv_set*v> routine
+you called first. This is because every C<sv_set*v> routine turns on
+only the bit for the particular type of data being set, and turns off
+all the rest.
+
+For example, to create a new Perl variable called "dberror" that contains
+both the numeric and descriptive string error values, you could use the
+following code:
+
+ extern int dberror;
+ extern char *dberror_list;
+
+ SV* sv = perl_get_sv("dberror", TRUE);
+ sv_setiv(sv, (IV) dberror);
+ sv_setpv(sv, dberror_list[dberror]);
+ SvIOK_on(sv);
+
+If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
+macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
+
+=head2 Magic Variables
[This section still under construction. Ignore everything here. Post no
bills. Everything not permitted is forbidden.]
i vtbl_isaelem @ISA array element
L 0 (but sets RMAGICAL) Perl Module/Debugger???
l vtbl_dbline Debugger?
+ o vtbl_collxfrm Locale transformation
P vtbl_pack Tied Array or Hash
p vtbl_packelem Tied Array or Hash element
q vtbl_packelem Tied Scalar or Handle
U vtbl_uvar ???
v vtbl_vec Vector
x vtbl_substr Substring???
- y vtbl_vivary Shadow variable in foreach loop
+ y vtbl_itervar Shadow "foreach" iterator variable
* vtbl_glob GV???
# vtbl_arylen Array Length
. vtbl_pos $. scalar variable
field is an upper-case letter, then the mg_obj is copied to C<nsv>, but
the mg_type field is changed to be the lower-case letter.
-=head2 Double-Typed SV's
-
-Scalar variables normally contain only one type of value, an integer,
-double, pointer, or reference. Perl will automatically convert the
-actual scalar data from the stored type into the requested type.
-
-Some scalar variables contain more than one type of scalar data. For
-example, the variable C<$!> contains either the numeric value of C<errno>
-or its string equivalent from either C<strerror> or C<sys_errlist[]>.
-
-To force multiple data values into an SV, you must do two things: use the
-C<sv_set*v> routines to add the additional scalar type, then set a flag
-so that Perl will believe it contains more than one type of data. The
-four macros to set the flags are:
-
- SvIOK_on
- SvNOK_on
- SvPOK_on
- SvROK_on
-
-The particular macro you must use depends on which C<sv_set*v> routine
-you called first. This is because every C<sv_set*v> routine turns on
-only the bit for the particular type of data being set, and turns off
-all the rest.
-
-For example, to create a new Perl variable called "dberror" that contains
-both the numeric and descriptive string error values, you could use the
-following code:
-
- extern int dberror;
- extern char *dberror_list;
-
- SV* sv = perl_get_sv("dberror", TRUE);
- sv_setiv(sv, (IV) dberror);
- sv_setpv(sv, dberror_list[dberror]);
- SvIOK_on(sv);
-
-If the order of C<sv_setiv> and C<sv_setpv> had been reversed, then the
-macro C<SvPOK_on> would need to be called instead of C<SvIOK_on>.
+=head1 Subroutines
=head2 XSUB's and the Argument Stack
For a complete description of the PerlIO abstraction, consult L<perlapio>.
-=head2 Scratchpads
-
-=head3 Putting a C value on Perl stack
+=head2 Putting a C value on Perl stack
A lot of opcodes (this is an elementary operation in the internal perl
stack machine) put an SV* on the stack. However, as an optimization
reuse specially assigned SVs (I<target>s) which are (as a corollary)
not constantly freed/created.
-Each of the targets is created only once (but see
+Each of the targets is created only once (but see
L<Scratchpads and recursion> below), and when an opcode needs to put
an integer, a double, or a string on stack, it just sets the
corresponding parts of its I<target> and puts the I<target> on stack.
directly used in some opcodes, as well as indirectly in zillions of
others, which use it via C<(X)PUSH[pni]>.
-=head3 Scratchpads
+=head2 Scratchpads
The question remains on when the SV's which are I<target>s for opcodes
are created. The answer is that they are created when the current unit --
OP's in the compile tree of the unit can use the same target, if this
would not conflict with the expected life of the temporary.
-=head3 Scratchpads and recursions
+=head2 Scratchpads and recursion
In fact it is not 100% true that a compiled unit contains a pointer to
the scratchpad AV. In fact it contains a pointer to an AV of
The I<target>s on this scratchpad are C<undef>s, but they are already
marked with correct flags.
-=head2 API LISTING
+=head1 Compiled code
+
+=head2 Code tree
+
+Here we describe the internal form your code is converted to by
+Perl. Start with a simple example:
+
+ $a = $b + $c;
+
+This is converted to a tree similar to this one:
+
+ assign-to
+ / \
+ + $a
+ / \
+ $b $c
+
+(but slightly more complicated). This tree reflect the way Perl
+parsed your code, but has nothing to do with the execution order.
+There is an additional "thread" going through the nodes of the tree
+which shows the order of execution of the nodes. In our simplified
+example above it looks like:
+
+ $b ---> $c ---> + ---> $a ---> assign-to
+
+But with the actual compile tree for C<$a = $b + $c> it is different:
+some nodes I<optimized away>. As a corollary, though the actual tree
+contains more nodes than our simplified example, the execution order
+is the same as in our example.
+
+=head2 Examining the tree
+
+If you have your perl compiled for debugging (usually done with C<-D
+optimize=-g> on C<Configure> command line), you may examine the
+compiled tree by specifying C<-Dx> on the Perl command line. The
+output takes several lines per node, and for C<$b+$c> it looks like
+this:
+
+ 5 TYPE = add ===> 6
+ TARG = 1
+ FLAGS = (SCALAR,KIDS)
+ {
+ TYPE = null ===> (4)
+ (was rv2sv)
+ FLAGS = (SCALAR,KIDS)
+ {
+ 3 TYPE = gvsv ===> 4
+ FLAGS = (SCALAR)
+ GV = main::b
+ }
+ }
+ {
+ TYPE = null ===> (5)
+ (was rv2sv)
+ FLAGS = (SCALAR,KIDS)
+ {
+ 4 TYPE = gvsv ===> 5
+ FLAGS = (SCALAR)
+ GV = main::c
+ }
+ }
+
+This tree has 5 nodes (one per C<TYPE> specifier), only 3 of them are
+not optimized away (one per number in the left column). The immediate
+children of the given node correspond to C<{}> pairs on the same level
+of indentation, thus this listing corresponds to the tree:
+
+ add
+ / \
+ null null
+ | |
+ gvsv gvsv
+
+The execution order is indicated by C<===E<gt>> marks, thus it is C<3
+4 5 6> (node C<6> is not included into above listing), i.e.,
+C<gvsv gvsv add whatever>.
+
+=head2 Compile pass 1: check routines
+
+The tree is created by the I<pseudo-compiler> while yacc code feeds it
+the constructions it recognizes. Since yacc works bottom-up, so does
+the first pass of perl compilation.
+
+What makes this pass interesting for perl developers is that some
+optimization may be performed on this pass. This is optimization by
+so-called I<check routines>. The correspondence between node names
+and corresponding check routines is described in F<opcode.pl> (do not
+forget to run C<make regen_headers> if you modify this file).
+
+A check routine is called when the node is fully constructed except
+for the execution-order thread. Since at this time there is no
+back-links to the currently constructed node, one can do most any
+operation to the top-level node, including freeing it and/or creating
+new nodes above/below it.
+
+The check routine returns the node which should be inserted into the
+tree (if the top-level node was not modified, check routine returns
+its argument).
+
+By convention, check routines have names C<ck_*>. They are usually
+called from C<new*OP> subroutines (or C<convert>) (which in turn are
+called from F<perly.y>).
+
+=head2 Compile pass 1a: constant folding
+
+Immediately after the check routine is called the returned node is
+checked for being compile-time executable. If it is (the value is
+judged to be constant) it is immediately executed, and a I<constant>
+node with the "return value" of the corresponding subtree is
+substituted instead. The subtree is deleted.
+
+If constant folding was not performed, the execution-order thread is
+created.
+
+=head2 Compile pass 2: context propagation
+
+When a context for a part of compile tree is known, it is propagated
+down through the tree. Aat this time the context can have 5 values
+(instead of 2 for runtime context): void, boolean, scalar, list, and
+lvalue. In contrast with the pass 1 this pass is processed from top
+to bottom: a node's context determines the context for its children.
+
+Additional context-dependent optimizations are performed at this time.
+Since at this moment the compile tree contains back-references (via
+"thread" pointers), nodes cannot be free()d now. To allow
+optimized-away nodes at this stage, such nodes are null()ified instead
+of free()ing (i.e. their type is changed to OP_NULL).
+
+=head2 Compile pass 3: peephole optimization
+
+After the compile tree for a subroutine (or for an C<eval> or a file)
+is created, an additional pass over the code is performed. This pass
+is neither top-down or bottom-up, but in the execution order (with
+additional compilications for conditionals). These optimizations are
+done in the subroutine peep(). Optimizations performed at this stage
+are subject to the same restrictions as in the pass 2.
+
+=head1 API LISTING
This is a listing of functions, macros, flags, and variables that may be
useful to extension writers or that may be found while reading other
Used to indicate scalar context. See C<GIMME> and L<perlcall>.
+=item gv_fetchmeth
+
+Returns the glob with the given C<name> and a defined subroutine or
+C<NULL>. The glob lives in the given C<stash>, or in the stashes
+accessable via @ISA and @<UNIVERSAL>.
+
+The argument C<level> should be either 0 or -1. If C<level==0>, as a
+side-effect creates a glob with the given C<name> in the given
+C<stash> which in the case of success contains an alias for the
+subroutine, and sets up caching info for this glob. Similarly for all
+the searched stashes.
+
+This function grants C<"SUPER"> token as a postfix of the stash name.
+
+The GV returned from C<gv_fetchmeth> may be a method cache entry,
+which is not visible to Perl code. So when calling C<perl_call_sv>,
+you should not use the GV directly; instead, you should use the
+method's CV, which can be obtained from the GV with the C<GvCV> macro.
+
+ GV* gv_fetchmeth _((HV* stash, char* name, STRLEN len, I32 level));
+
+=item gv_fetchmethod
+
+Returns the glob which contains the subroutine to call to invoke the
+method on the C<stash>. In fact in the presense of autoloading this may
+be the glob for "AUTOLOAD". In this case the corresponing variable
+$AUTOLOAD is already setup.
+
+Note that if you want to keep this glob for a long time, you need to
+check for it being "AUTOLOAD", since at the later time the the call
+may load a different subroutine due to $AUTOLOAD changing its value.
+Use the glob created via a side effect to do this.
+
+This function grants C<"SUPER"> token as a prefix of the method name.
+
+Has the same side-effects and as C<gv_fetchmeth> with C<level==0>.
+C<name> should be writable if contains C<':'> or C<'\''>.
+The warning against passing the GV returned by C<gv_fetchmeth> to
+C<perl_call_sv> apply equally to C<gv_fetchmethod>.
+
+ GV* gv_fetchmethod _((HV* stash, char* name));
+
=item gv_stashpv
Returns a pointer to the stash for a specified package. If C<create> is set
Return the SV from the GV.
+=item he_delayfree
+
+Releases a hash entry, such as while iterating though the hash, but
+delays actual freeing of key and value until the end of the current
+statement (or thereabouts) with C<sv_2mortal>. See C<hv_iternext>.
+
+ void he_delayfree _((HV* hv, HE* hent));
+
+=item HEf_SVKEY
+
+This flag, used in the length slot of hash entries and magic
+structures, specifies the structure contains a C<SV*> pointer where a
+C<char*> pointer is to be expected. (For information only--not to be used).
+
=item he_free
-Releases a hash entry from an iterator. See C<hv_iternext>.
+Releases a hash entry, such as while iterating though the hash. See
+C<hv_iternext>.
+
+ void he_free _((HV* hv, HE* hent));
+
+=item HeHASH
+
+Returns the computed hash (type C<U32>) stored in the hash entry.
+
+ HeHASH(HE* he)
+
+=item HeKEY
+
+Returns the actual pointer stored in the key slot of the hash entry.
+The pointer may be either C<char*> or C<SV*>, depending on the value of
+C<HeKLEN()>. Can be assigned to. The C<HePV()> or C<HeSVKEY()> macros
+are usually preferable for finding the value of a key.
+
+ HeKEY(HE* he)
+
+=item HeKLEN
+
+If this is negative, and amounts to C<HEf_SVKEY>, it indicates the entry
+holds an C<SV*> key. Otherwise, holds the actual length of the key.
+Can be assigned to. The C<HePV()> macro is usually preferable for finding
+key lengths.
+
+ HeKLEN(HE* he)
+
+=item HePV
+
+Returns the key slot of the hash entry as a C<char*> value, doing any
+necessary dereferencing of possibly C<SV*> keys. The length of
+the string is placed in C<len> (this is a macro, so do I<not> use
+C<&len>). If you do not care about what the length of the key is,
+you may use the global variable C<na>. Remember though, that hash
+keys in perl are free to contain embedded nulls, so using C<strlen()>
+or similar is not a good way to find the length of hash keys.
+This is very similar to the C<SvPV()> macro described elsewhere in
+this document.
+
+ HePV(HE* he, STRLEN len)
+
+=item HeSVKEY
+
+Returns the key as an C<SV*>, or C<Nullsv> if the hash entry
+does not contain an C<SV*> key.
+
+ HeSVKEY(HE* he)
+
+=item HeSVKEY_force
+
+Returns the key as an C<SV*>. Will create and return a temporary
+mortal C<SV*> if the hash entry contains only a C<char*> key.
+
+ HeSVKEY_force(HE* he)
+
+=item HeSVKEY_set
+
+Sets the key to a given C<SV*>, taking care to set the appropriate flags
+to indicate the presence of an C<SV*> key, and returns the same C<SV*>.
+
+ HeSVKEY_set(HE* he, SV* sv)
+
+=item HeVAL
+
+Returns the value slot (type C<SV*>) stored in the hash entry.
+
+ HeVAL(HE* he)
=item hv_clear
SV* hv_delete _((HV* tb, char* key, U32 klen, I32 flags));
+=item hv_delete_ent
+
+Deletes a key/value pair in the hash. The value SV is removed from the hash
+and returned to the caller. The C<flags> value will normally be zero; if set
+to G_DISCARD then null will be returned. C<hash> can be a valid pre-computed
+hash value, or 0 to ask for it to be computed.
+
+ SV* hv_delete_ent _((HV* tb, SV* key, I32 flags, U32 hash));
+
=item hv_exists
Returns a boolean indicating whether the specified hash key exists. The
bool hv_exists _((HV* tb, char* key, U32 klen));
+=item hv_exists_ent
+
+Returns a boolean indicating whether the specified hash key exists. C<hash>
+can be a valid pre-computed hash value, or 0 to ask for it to be computed.
+
+ bool hv_exists_ent _((HV* tb, SV* key, U32 hash));
+
=item hv_fetch
Returns the SV which corresponds to the specified key in the hash. The
SV** hv_fetch _((HV* tb, char* key, U32 klen, I32 lval));
+=item hv_fetch_ent
+
+Returns the hash entry which corresponds to the specified key in the hash.
+C<hash> must be a valid pre-computed hash number for the given C<key>, or
+0 if you want the function to compute it. IF C<lval> is set then the
+fetch will be part of a store. Make sure the return value is non-null
+before accessing it. The return value when C<tb> is a tied hash
+is a pointer to a static location, so be sure to make a copy of the
+structure if you need to store it somewhere.
+
+ HE* hv_fetch_ent _((HV* tb, SV* key, I32 lval, U32 hash));
+
=item hv_iterinit
Prepares a starting point to traverse a hash table.
char* hv_iterkey _((HE* entry, I32* retlen));
+=item hv_iterkeysv
+
+Returns the key as an C<SV*> from the current position of the hash
+iterator. The return value will always be a mortal copy of the
+key. Also see C<hv_iterinit>.
+
+ SV* hv_iterkeysv _((HE* entry));
+
=item hv_iternext
Returns entries from a hash iterator. See C<hv_iterinit>.
SV** hv_store _((HV* tb, char* key, U32 klen, SV* val, U32 hash));
+=item hv_store_ent
+
+Stores C<val> in a hash. The hash key is specified as C<key>. The C<hash>
+parameter is the pre-computed hash value; if it is zero then Perl will
+compute it. The return value is the new hash entry so created. It will be
+null if the operation failed or if the entry was stored in a tied hash.
+Otherwise the contents of the return value can be accessed using the
+C<He???> macros described here.
+
+ HE* hv_store_ent _((HV* tb, SV* key, SV* val, U32 hash));
+
=item hv_undef
Undefines the hash.
it will be upgraded to one. If C<classname> is non-null then the new SV will
be blessed in the specified package. The new SV is returned and its
reference count is 1.
+
SV* newSVrv _((SV* rv, char* classname));
=item newSVsv
=head1 EDITOR
-Jeff Okamoto <okamoto@corp.hp.com>
+Jeff Okamoto <F<okamoto@corp.hp.com>>
With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
Bowers, Matthew Green, Tim Bunce, Spider Boardman, and Ulrich Pfeifer.
-API Listing by Dean Roehrich <roehrich@cray.com>.
+API Listing by Dean Roehrich <F<roehrich@cray.com>>.
=head1 DATE
-Version 26.1: 1996/12/20
+Version 31.2: 1997/3/5
projects / p5sagit/p5-mst-13.2.git / blobdiff