@node GCL Specific, C Interface, Type, Top
@chapter GCL Specific

@defun SYSTEM (string)
Package:LISP

GCL specific: Executes a Shell command as if STRING is an input to the
Shell.  Not all versions of GCL support this function.  At least on
POSIX systems, this call should return two integers represeting the
exit status and any possible terminating signal respectively.


@end defun

@defvar *IGNORE-MAXIMUM-PAGES* 
Package:SI
GCL specific: Tells the GCL memory manager whether (non-NIL) or not (NIL) it
should expand memory whenever the maximum allocatable pages have been used
up.


@end defvar

@defvar *OPTIMIZE-MAXIMUM-PAGES* 
Package:SI

GCL specific: Tells the GCL memory manager whether to attempt to
adjust the maximum allowable pages for each type to approximately
optimize the garbage collection load in the current process.  Defaults
to T.  Set to NIL if you care more about memory usage than runtime.


@end defvar

@defun MACHINE-VERSION ()
Package:LISP

Returns a string that identifies the machine version of the machine
on which GCL is currently running.


@end defun

@defun BY ()
Package:LISP

GCL specific: Exits from GCL.


@end defun

@deffn {Macro} DEFCFUN 
Package:LISP

Syntax:
@example
(defcfun header n @{element@}*)
@end example


GCL specific: Defines a C-language function which calls Lisp functions
and/or handles Lisp objects.  HEADER gives the header of the C
function as a string.  Non-negative-integer is the number of the main
stack entries used by the C function, primarily for protecting Lisp
objects from being garbage-collected.  Each ELEMENT may give a C code
fragment as a string, or it may be a list
	((symbol @{arg@}*) @{place@}*)
which, when executed, calls the Lisp function named by SYMBOL with the
specified arguments and saves the value(s) to the specified places.
The DEFCFUN form has the above meanings only after compiled;  The GCL
interpreter simply ignores this form.

An example which defines a C function list2 of two arguments, but which 
calls the 'lisp' function CONS by name, and refers to the constant 'NIL.
Note to be loaded by @code{load} the function should be static.


(defCfun "static object list2(x,y) object x,y;" 0
              "object z;"
               ('NIL z)
               ((CONS y z) z)
               ((CONS x z) z)
         	"return(z);"
)

In lisp the operations in the body would be
   (setq z 'nil)
   (setq z (cons y z))
   (setq z (cons x z))
   


Syntax:
@example

        (defCfun header non-negative-integer
                @{ string
                  | ( function-symbol @{ value @}* )
                  | (( function-symbol  @{ value @}* ) @{ place @}* ) @})


value:
place:
         @{ C-expr | ( C-type C-expr ) @}

C-function-name:
C-expr:
         @{ string | symbol @}
 
C-type:
         @{ object | int | char | float | double @}

@end example




@end deffn

@deffn {Macro} CLINES 
Package:LISP

Syntax:
@example
(clines @{string@}*)
@end example

GCL specific:  The GCL compiler embeds STRINGs into the intermediate C
language code.  The interpreter ignores this form.


@end deffn

@defun ALLOCATE (type number &optional (really-allocate nil))
Package:LISP

GCL specific: Sets the maximum number of pages for the type class of the
GCL implementation type TYPE to NUMBER.  If REALLY-ALLOCATE is given a
non-NIL value, then the specified number of pages will be allocated
immediately.


@end defun

@defun GBC (x)
Package:LISP

GCL specific: Invokes the garbage collector (GC) with the collection level
specified by X.  NIL as the argument causes GC to collect cells only.  T as
the argument causes GC to collect everything.


@end defun

@defun SAVE (pathname)
Package:LISP

GCL specific: Saves the current GCL core image into a program file specified
by PATHNAME.  This function depends on the version of GCL.  The function
si::save-system is to be preferred in almost all circumstances.   Unlike
save, it makes the relocatable section permanent, and causes no future gc of
currently loaded .o files.

@end defun

@defun HELP* (string &optional (package 'lisp))
Package:LISP

GCL specific: Prints the documentation associated with those symbols in the
specified package whose print names contain STRING as substring.  STRING may
be a symbol, in which case the print-name of that symbol is used.  If PACKAGE
is NIL, then all packages are searched.


@end defun

@deffn {Macro} DEFLA 
Package:LISP

Syntax:
@example
(defla name lambda-list @{decl | doc@}* @{form@}*)
@end example

GCL specific: Used to DEFine Lisp Alternative.  For the interpreter, DEFLA is
equivalent to DEFUN, but the compiler ignores this form.


@end deffn

@defun PROCLAMATION (decl-spec)
Package:LISP

GCL specific: Returns T if the specified declaration is globally in effect;
NIL otherwise.  See the doc of DECLARE for possible DECL-SPECs.


@end defun

@deffn {Macro} DEFENTRY 
Package:LISP

Syntax:
@example
(defentry name arg-types c-function)
@end example


GCL specific: The compiler defines a Lisp function whose body consists of a
calling sequence to the C language function specified by C-FUNCTION.  The
interpreter ignores this form.  The ARG-TYPES specifies the C types of the
arguments which C-FUNCTION requires.  The list of allowed types is (object
char int float double string).  Code will be produced to coerce from a lisp
object to the appropriate type before passing the argument to the C-FUNCTION.
The c-function should be of the form (c-result-type c-fname) where
c-result-type is a member of (void object char int float double string).
c-fname may be a symbol (in which case it will be downcased) or a string.  If
c-function is not a list, then (object c-function) is assumed.  In order
for C code to be loaded in by @code{load} you should declare any
variables and functions to be static.   If you will link them in
at build time, of course you are allowed to define new externals.

@example
  Sample usage:
--File begin-----
;; JOE takes X a lisp string and Y a fixnum and returns a character.
(clines "#include \"foo.ch\"")
(defentry joe (string int) (char "our_c_fun"))
---File end------
---File foo.ch---
/* C function for extracting the i'th element of a string */
static char our_c_fun(p,i)
char *p;
int i;
   @{
	return p[i];
   @}
-----File end---
@end example

One must be careful of storage allocation issues when passing a string.
If the C code invokes storage allocation (either by calling @code{malloc}
or @code{make_cons} etc), then there is a possibility of a garbage
collection, so that if the string passed was not constructed with
@code{:static t} when its array was constructed, then it could move.
If the C function may allocate storage, then you should pass a copy:
@example
(defun safe-c-string (x)
  (let* ((n (length x))
         (a (make-array (+ n 1) :element-type 'string-char
           :static t :fill-pointer n)))
    (si::copy-array-portion x y 0 0 n)
    (setf (aref a n) (code-char 0)))
    a)

@end example


@end deffn
@defun COPY-ARRAY-PORTION (x,y,i1,i2,n1)
Package:SI
Copy elements from X to Y starting at X[i1] to Y[i2] and doing N1
elements if N1 is supplied otherwise, doing the length of X - I1
elements.  If the types of the arrays are not the same, this has
implementation dependent results.
@end defun

@defun BYE ( &optional (exit-status 0))
Package:LISP

GCL specific: Exits from GCL with exit-status.


@end defun

@defun USE-FAST-LINKS (turn-on)
Package:LISP

GCL specific: If TURN-ON is not nil, the fast link mechanism is enabled,
so that ordinary function calls will not appear in the invocation stack,
and calls will be much faster.  This is the default.   If you anticipate
needing to see a stack trace in the debugger, then you should turn this
off.


@end defun

@menu
* Bignums::			
@end menu

@node Bignums,  , GCL Specific, GCL Specific
@section Bignums

A directory mp was added to hold the new multi precision arithmetic
code.  The layout and a fair amount of code in the mp directory is an
enhanced version of gpari version 34. The gpari c code was rewritten
to be more efficient, and gcc assembler macros were added to allow
inlining of operations not possible to do in C.  On a 68K machine,
this allows the C version to be as efficient as the very carefully
written assembler in the gpari distribution.  For the main machines,
an assembler file (produced by gcc) based on this new method, is
included.   This is for sites which do not have gcc, or do not
wish to compile the whole system with gcc.

Bignum arithmetic is much faster now.  Many changes were made to
cmpnew also, to add 'integer' as a new type.  It differs from
variables of other types, in that storage is associated to each such
variable, and assignments mean copying the storage.  This allows a
function which does a good deal of bignum arithmetic, to do very
little consing in the heap.  An example is the computation of PI-INV
in scratchpad, which calculates the inverse of pi to a prescribed
number of bits accuracy.  That function is now about 20 times faster,
and no longer causes garbage collection.  In versions of GCL  where
HAVE_ALLOCA is defined, the temporary storage growth is on the C
stack, although this often not so critical (for example it makes
virtually no difference in the PI-INV example, since in spite of the
many operations, only one storage allocation takes place.
	
Below is the actual code for PI-INV

On a sun3/280 (cli.com)

Here is the comparison of lucid and gcl before and after
on that pi-inv.   Times are in seconds with multiples of the
gcl/akcl time in parentheses.

On a sun3/280 (cli.com)

@example

pi-inv   akcl-566  franz        lucid         old kcl/akcl
----------------------------------------
10000      3.3     9.2(2.8 X)  15.3 (4.6X)    92.7   (29.5 X)
20000      12.7    31.0(2.4 X) 62.2 (4.9X)    580.0  (45.5 X)


(defun pi-inv (bits &aux (m 0))
  (declare (integer bits m))
  (let* ((n (+ bits (integer-length bits) 11))
         (tt (truncate (ash 1 n) 882))
         (d (* 4 882 882))
         (s 0))
    (declare (integer s d tt n))
    (do ((i 2 (+ i 2))
         (j 1123 (+ j 21460)))
        ((zerop tt) (cons s (- (+ n 2))))
      (declare (integer i j))
        (setq s (+ s (* j tt))
              m (- (* (- i 1) (- (* 2 i) 1) (- (* 2 i) 3)))
              tt (truncate (* m tt) (* d (the integer (expt i 3))))))))

@end example
