## 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 foreign pointer object.
pointer-like object
  is a closure, port, 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

address->pointer ADDRESS procedure

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

#### allocate

allocate BYTES procedure

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

  This procedure could be defined as follows:

      (define allocate (foreign-lambda c-pointer "malloc" integer))

#### free

free POINTER procedure

  Frees the memory pointed to by POINTER.

  This procedure could be defined as follows:

      (define free (foreign-lambda void "free" c-pointer))

#### object->pointer

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

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?

pointer? X procedure

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

#### pointer-like?

pointer-like? X procedure

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

#### pointer=?

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

pointer->address POINTER*procedure

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

#### pointer+

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

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

pointer-u8-ref POINTER procedure

  Returns the unsigned byte at the address designated by POINTER.

#### pointer-s8-ref

pointer-s8-ref POINTER procedure

  Returns the signed byte at the address designated by POINTER.

#### pointer-u16-ref

pointer-u16-ref POINTER procedure

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

#### pointer-s16-ref

pointer-s16-ref POINTER procedure

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

#### pointer-u32-ref

pointer-u32-ref POINTER procedure

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

#### pointer-s32-ref

pointer-s32-ref POINTER procedure

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

#### pointer-u64-ref

pointer-u64-ref POINTER procedure

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

#### pointer-s64-ref

pointer-s64-ref POINTER procedure

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

#### pointer-f32-ref

pointer-f32-ref POINTER procedure

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

#### pointer-f64-ref

pointer-f64-ref POINTER procedure

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

#### pointer-u8-set!

pointer-u8-set! POINTER N procedure
set! (pointer-u8-ref POINTER) N procedure

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

#### pointer-s8-set!

pointer-s8-set! POINTER N procedure
set! (pointer-s8-ref POINTER) N procedure

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

#### pointer-u16-set!

pointer-u16-set! POINTER N procedure
set! (pointer-u16-ref POINTER) N procedure

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

#### pointer-s16-set!

pointer-s16-set! POINTER N procedure
set! (pointer-s16-ref POINTER) N procedure

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

#### pointer-u32-set!

pointer-u32-set! POINTER N procedure
set! (pointer-u32-ref POINTER) N procedure

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

#### pointer-s32-set!

pointer-s32-set! POINTER N procedure
set! (pointer-s32-ref POINTER) N procedure

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

#### pointer-u64-set!

pointer-u64-set! POINTER N procedure
set! (pointer-u64-ref POINTER) N procedure

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

#### pointer-s64-set!

pointer-s64-set! POINTER N procedure
set! (pointer-s64-ref POINTER) N procedure

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

#### pointer-f32-set!

pointer-f32-set! POINTER N 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!

pointer-f64-set! POINTER N 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

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?

tagged-pointer? X #!optional 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

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

make-pointer-vector LENGTH #!optional 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?

pointer-vector? X procedure

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

#### pointer-vector

pointer-vector POINTER ...procedure

  Returns a pointer-vector from the given pointer arguments.

#### pointer-vector-length

pointer-vector-length POINTERVECTOR procedure

  Returns the length of the given pointer-vector.

#### pointer-vector-ref

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!

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!

pointer-vector-fill! POINTERVECTOR POINTER procedure

  Set every element in the POINTERVECTOR to POINTER.

### Moving memory

#### move-memory!

move-memory! FROM TO #!optional BYTES FROM-OFFSET TO-OFFSET procedure

  Copies BYTES bytes of memory from FROM to TO. FROM and TO may be strings, blobs, 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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