Module (chicken memory)

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== Module (chicken memory)

The procedures from this module operate directly on memory, at a very
low level.  This makes them unsafe, unlike most other Scheme
procedures.  '''Use at your own risk.'''

=== Foreign pointers

The abstract class of ''pointer'' is divided into 2 categories: 

; ''pointer object'' : is a regular or [[#Tagged pointers|tagged]] foreign pointer object.

; ''pointer-like object'' : is a closure, port, [[Module (chicken locative)|locative]], or a pointer object.

Note that Locatives, while technically pointers, are not considered a ''pointer
object'', but a ''pointer-like object''. The distinction is artificial.


==== address->pointer

<procedure>(address->pointer ADDRESS)</procedure>

Creates a new foreign pointer object initialized to point to the address
given in the integer {{ADDRESS}}.


==== allocate

<procedure>(allocate BYTES)</procedure>

Returns a foreign pointer object to a freshly allocated region of static
memory.

This procedure could be defined as follows:

<enscript highlight=scheme>
(define allocate (foreign-lambda c-pointer "malloc" integer))
</enscript>


==== free

<procedure>(free POINTER)</procedure>

Frees the memory pointed to by {{POINTER}}.

This procedure could be defined as follows:

<enscript highlight=scheme>
(define free (foreign-lambda void "free" c-pointer))
</enscript>


==== object->pointer

<procedure>(object->pointer X)</procedure>

Returns a foreign pointer object pointing to the Scheme object X, which should
be a non-immediate object. ("foreign" here is a bit of a misnomer.)

Note that data in the garbage collected heap moves during garbage collection.


==== pointer->object

<procedure>(pointer->object POINTER)</procedure>

Returns the Scheme object pointed to by the pointer object {{POINTER}}.

Whether the {{POINTER}} actually points to a Scheme object is not guaranteed. Use
at your own risk.

==== pointer?

<procedure>(pointer? X)</procedure>

Returns {{#t}} if {{X}} is a pointer object, or {{#f}} otherwise.


==== pointer-like?

<procedure>(pointer-like? X)</procedure>

Returns {{#t}} if {{X}} is a pointer-like object, or {{#f}} otherwise.


==== pointer=?

<procedure>(pointer=? POINTER*1 POINTER*2)</procedure>

Returns {{#t}} if the pointer-like objects {{POINTER*1}} and {{POINTER*2}} point
to the same address, or {{#f}} otherwise.


==== pointer->address

<procedure>(pointer->address POINTER*)</procedure>

Returns the address, to which the pointer-like object {{POINTER*}} points.


==== pointer+

<procedure>(pointer+ POINTER* N)</procedure>

Returns a new foreign pointer object representing the pointer-like object
{{POINTER*}} address value increased by the byte-offset {{N}}.

Use of anything other than a pointer object as an argument is questionable.


==== align-to-word

<procedure>(align-to-word POINTER*-OR-INT)</procedure>

Accepts either a pointer-like object or an integer as the argument and returns
a new foreign pointer or integer aligned to the native word size of the host
platform.

Use of anything other than an integer or pointer object as an argument is
questionable.


=== SRFI-4 Foreign pointers

These procedures actually accept a pointer-like object as the {{POINTER}} argument.
However, as usual, use of anything other than a pointer object is questionable.


==== pointer-u8-ref

<procedure>(pointer-u8-ref POINTER)</procedure>

Returns the unsigned byte at the address designated by {{POINTER}}.


==== pointer-s8-ref

<procedure>(pointer-s8-ref POINTER)</procedure>

Returns the signed byte at the address designated by {{POINTER}}.


==== pointer-u16-ref

<procedure>(pointer-u16-ref POINTER)</procedure>

Returns the unsigned 16-bit integer at the address designated by {{POINTER}}.


==== pointer-s16-ref

<procedure>(pointer-s16-ref POINTER)</procedure>

Returns the signed 16-bit integer at the address designated by {{POINTER}}.


==== pointer-u32-ref

<procedure>(pointer-u32-ref POINTER)</procedure>

Returns the unsigned 32-bit integer at the address designated by {{POINTER}}.


==== pointer-s32-ref

<procedure>(pointer-s32-ref POINTER)</procedure>

Returns the signed 32-bit integer at the address designated by {{POINTER}}.

==== pointer-u64-ref

<procedure>(pointer-u64-ref POINTER)</procedure>

Returns the unsigned 64-bit integer at the address designated by {{POINTER}}.


==== pointer-s64-ref

<procedure>(pointer-s64-ref POINTER)</procedure>

Returns the signed 64-bit integer at the address designated by {{POINTER}}.


==== pointer-f32-ref

<procedure>(pointer-f32-ref POINTER)</procedure>

Returns the 32-bit float at the address designated by {{POINTER}}.


==== pointer-f64-ref

<procedure>(pointer-f64-ref POINTER)</procedure>

Returns the 64-bit double at the address designated by {{POINTER}}.


==== pointer-u8-set!

<procedure>(pointer-u8-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-u8-ref POINTER) N)</procedure>

Stores the unsigned byte {{N}} at the address designated by {{POINTER}}.


==== pointer-s8-set!

<procedure>(pointer-s8-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-s8-ref POINTER) N)</procedure>

Stores the signed byte {{N}} at the address designated by {{POINTER}}.


==== pointer-u16-set!

<procedure>(pointer-u16-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-u16-ref POINTER) N)</procedure>

Stores the unsigned 16-bit integer {{N}} at the address designated by {{POINTER}}.


==== pointer-s16-set!

<procedure>(pointer-s16-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-s16-ref POINTER) N)</procedure>

Stores the signed 16-bit integer {{N}} at the address designated by {{POINTER}}.


==== pointer-u32-set!

<procedure>(pointer-u32-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-u32-ref POINTER) N)</procedure>

Stores the unsigned 32-bit integer {{N}} at the address designated by {{POINTER}}.


==== pointer-s32-set!

<procedure>(pointer-s32-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-s32-ref POINTER) N)</procedure>

Stores the 32-bit integer {{N}} at the address designated by {{POINTER}}.


==== pointer-u64-set!

<procedure>(pointer-u64-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-u64-ref POINTER) N)</procedure>

Stores the unsigned 64-bit integer {{N}} at the address designated by {{POINTER}}.


==== pointer-s64-set!

<procedure>(pointer-s64-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-s64-ref POINTER) N)</procedure>

Stores the 64-bit integer {{N}} at the address designated by {{POINTER}}.


==== pointer-f32-set!

<procedure>(pointer-f32-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-f32-ref POINTER) N)</procedure>

Stores the 32-bit floating-point number {{N}} at the address designated by {{POINTER}}.


==== pointer-f64-set!

<procedure>(pointer-f64-set! POINTER N)</procedure><br>
<procedure>(set! (pointer-f64-ref POINTER) N)</procedure>

Stores the 64-bit floating-point number {{N}} at the address designated by {{POINTER}}.



=== Tagged pointers

''Tagged'' pointers are foreign pointer objects with an extra tag object.


==== tag-pointer

<procedure>(tag-pointer POINTER* TAG)</procedure>

Creates a new tagged foreign pointer object from the pointer-like object
{{POINTER*}} with the tag {{TAG}}, which may an arbitrary Scheme object.

Use of anything other than a pointer object is questionable.

==== tagged-pointer?

<procedure>(tagged-pointer? X [TAG])</procedure>

Returns {{#t}} if {{X}} is a tagged foreign pointer object, or {{#f}} otherwise.

Further, returns {{#t}} when {{X}} has the optional tag {{TAG}} (using an
{{equal?}} comparison), or {{#f}} otherwise.


==== pointer-tag

<procedure>(pointer-tag POINTER*)</procedure>

If {{POINTER}} is a tagged foreign pointer object, its tag is returned. If {{POINTER*}}
is any other kind of pointer-like object {{#f}} is returned. Otherwise an
error is signalled.


=== Pointer vectors

''Pointer vectors'' are specialized and space-efficient vectors for
foreign pointer objects. All procedures defined below that accept
a pointer object allow {{#f}} as an alternative representation of
the {{NULL}}-pointer.


==== make-pointer-vector 

<procedure>(make-pointer-vector LENGTH [INIT])</procedure>

Creates a pointer-vector of the given length and optionally initializes each
element to {{INIT}}, which should be a pointer or {{#f}}, which represents the
{{NULL}} pointer.

==== pointer-vector?

<procedure>(pointer-vector? X)</procedure>

Returns {{#t}} if {{X}} is a pointer-vector or {{#f}} otherwise.

==== pointer-vector

<procedure>(pointer-vector POINTER ...)</procedure>

Returns a pointer-vector from the given pointer arguments.

==== pointer-vector-length

<procedure>(pointer-vector-length POINTERVECTOR)</procedure>

Returns the length of the given pointer-vector.

==== pointer-vector-ref

<procedure>(pointer-vector-ref POINTERVECTOR INDEX)</procedure>

Returns the pointer at {{INDEX}} in the given pointer-vector or
{{#f}} if the element is a {{NULL}}- pointer.

==== pointer-vector-set!

<procedure>(pointer-vector-set! POINTERVECTOR INDEX POINTER)</procedure>

Sets the element at the position {{INDEX}} in the given pointer-vector to
{{POINTER}}. The alternative syntax

  (set! (pointer-vector-ref POINTERVECTOR INDEX) POINTER)

is also allowed.

==== pointer-vector-fill!

<procedure>(pointer-vector-fill! POINTERVECTOR POINTER)</procedure>

Set every element in the {{POINTERVECTOR}} to {{POINTER}}.


=== Moving memory

==== move-memory!

<procedure>(move-memory! FROM TO [BYTES [FROM-OFFSET [TO-OFFSET]]])</procedure>

Copies {{BYTES}} bytes of memory from {{FROM}} to {{TO}}. {{FROM}} and {{TO}}
may be strings, blobs, [[Module srfi-4|SRFI-4 number-vectors]], memory
mapped files, foreign pointers (as obtained from a call to {{foreign-lambda}},
for example), tagged-pointers or locatives. if {{BYTES}} is not given and the
size of the source or destination operand is known then the maximal number of
bytes will be copied. Moving memory to the storage returned by locatives will
cause havoc, if the locative refers to containers of non-immediate data, like
vectors or pairs.

The additional fourth and fifth argument specify starting offsets (in bytes)
for the source and destination arguments.

Signals an error if any of the above constraints is violated.

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