Buffer protocol proposal (#3261)

* Add buffer protocol

* Modify for some review comments

* Per-object buffer availability

* Rename to MemoryView from Buffer and make compilable

* Support integral repeat count in memory view format

* Support 'x' for padding bytes

* Add rb_memory_view_parse_item_format

* Check type in rb_memory_view_register

* Update dependencies in common.mk

* Add test of MemoryView

* Add test of rb_memory_view_init_as_byte_array

* Add native size format test

* Add MemoryView test utilities

* Add test of rb_memory_view_fill_contiguous_strides

* Skip spaces in format string

* Support endianness specifiers

* Update documentation

* Support alignment

* Use RUBY_ALIGNOF

* Fix format parser to follow the pack format

* Support the _ modifier

* Parse count specifiers in get_format_size function.

* Use STRUCT_ALIGNOF

* Fix test

* Fix test

* Fix total size for the case with tail padding

* Fix rb_memory_view_get_item_pointer

* Fix rb_memory_view_parse_item_format again

1 files changed, 136 insertions, 0 deletions

diff --git a/include/ruby/memory_view.h b/include/ruby/memory_view.h
new file mode 100644
index 0000000000..dc6c971593
--- /dev/null
+++ b/include/ruby/memory_view.h
@@ -0,0 +1,136 @@
+#ifndef RUBY_MEMORY_VIEW_H
+#define RUBY_MEMORY_VIEW_H 1
+/**
+ * @file
+ * @author     Ruby developers <ruby-core@ruby-lang.org>
+ * @copyright  This  file  is   a  part  of  the   programming  language  Ruby.
+ *             Permission  is hereby  granted,  to  either redistribute  and/or
+ *             modify this file, provided that  the conditions mentioned in the
+ *             file COPYING are met.  Consult the file for details.
+ * @brief      Memory View.
+ */
+
+#include "ruby/internal/dllexport.h"
+#include "ruby/internal/stdbool.h"
+#include "ruby/internal/value.h"
+#include "ruby/intern.h"
+
+enum ruby_memory_view_flags {
+    RUBY_MEMORY_VIEW_SIMPLE            = 0,
+    RUBY_MEMORY_VIEW_WRITABLE          = (1<<0),
+    RUBY_MEMORY_VIEW_FORMAT            = (1<<1),
+    RUBY_MEMORY_VIEW_MULTI_DIMENSIONAL = (1<<2),
+    RUBY_MEMORY_VIEW_STRIDES           = (1<<3) | RUBY_MEMORY_VIEW_MULTI_DIMENSIONAL,
+    RUBY_MEMORY_VIEW_ROW_MAJOR         = (1<<4) | RUBY_MEMORY_VIEW_STRIDES,
+    RUBY_MEMORY_VIEW_COLUMN_MAJOR      = (1<<5) | RUBY_MEMORY_VIEW_STRIDES,
+    RUBY_MEMORY_VIEW_ANY_CONTIGUOUS    = RUBY_MEMORY_VIEW_ROW_MAJOR | RUBY_MEMORY_VIEW_COLUMN_MAJOR,
+    RUBY_MEMORY_VIEW_INDIRECT          = (1<<6) | RUBY_MEMORY_VIEW_STRIDES,
+};
+
+typedef struct {
+    char format;
+    unsigned native_size_p: 1;
+    unsigned little_endian_p: 1;
+    size_t offset;
+    size_t size;
+    size_t repeat;
+} rb_memory_view_item_component_t;
+
+typedef struct {
+    /* The original object that have the memory exported via this memory view.
+     * The consumer of this memory view has the responsibility to call rb_gc_mark
+     * for preventing this obj collected by GC.  */
+    VALUE obj;
+
+    /* The pointer to the exported memory. */
+    void *data;
+
+    /* The number of bytes in data. */
+    ssize_t len;
+
+    /* 1 for readonly memory, 0 for writable memory. */
+    int readonly;
+
+    /* A string to describe the format of an element, or NULL for unsigned byte.
+     * The format string is a sequence the following pack-template specifiers:
+     *
+     *   c, C, s, s!, S, S!, n, v, i, i!, I, I!, l, l!,
+     *   L, L!, N, V, f, e, g, d, E, G, j, J, x
+     *
+     * For example, "dd" for an element that consists of two double values,
+     * and "CCC" for an element that consists of three bytes, such as
+     * a RGB color triplet.
+     *
+     * Also, the value endianness can be explicitly specified by '<' or '>'
+     * following a value type specifier.
+     */
+    const char *format;
+
+    /* The number of bytes in each element.
+     * item_size should equal to rb_memory_view_item_size_from_format(format). */
+    ssize_t item_size;
+
+    struct {
+        /* The array of rb_memory_view_item_component_t that describes the
+         * item structure. */
+        rb_memory_view_item_component_t *components;
+
+        /* The number of components in an item. */
+        ssize_t length;
+    } item_desc;
+
+    /* The number of dimension. */
+    int ndim;
+
+    /* ndim size array indicating the number of elements in each dimension.
+     * This can be NULL when ndim == 1. */
+    ssize_t *shape;
+
+    /* ndim size array indicating the number of bytes to skip to go to the
+     * next element in each dimension. */
+    ssize_t *strides;
+
+    /* The offset in each dimension when this memory view exposes a nested array.
+     * Or, NULL when this memory view exposes a flat array. */
+    ssize_t *sub_offsets;
+
+    /* the private data for managing this exported memory */
+    void *const private;
+} rb_memory_view_t;
+
+typedef int (* rb_memory_view_get_func_t)(VALUE obj, rb_memory_view_t *view, int flags);
+typedef int (* rb_memory_view_release_func_t)(VALUE obj, rb_memory_view_t *view);
+typedef int (* rb_memory_view_available_p_func_t)(VALUE obj);
+
+typedef struct {
+    rb_memory_view_get_func_t get_func;
+    rb_memory_view_release_func_t release_func;
+    rb_memory_view_available_p_func_t available_p_func;
+} rb_memory_view_entry_t;
+
+RBIMPL_SYMBOL_EXPORT_BEGIN()
+
+/* memory_view.c */
+bool rb_memory_view_register(VALUE klass, const rb_memory_view_entry_t *entry);
+
+#define rb_memory_view_is_contiguous(view) ( \
+    rb_memory_view_is_row_major_contiguous(view) \
+    || rb_memory_view_is_column_major_contiguous(view))
+
+int rb_memory_view_is_row_major_contiguous(const rb_memory_view_t *view);
+int rb_memory_view_is_column_major_contiguous(const rb_memory_view_t *view);
+void rb_memory_view_fill_contiguous_strides(const int ndim, const int item_size, const ssize_t *const shape, const int row_major_p, ssize_t *const strides);
+int rb_memory_view_init_as_byte_array(rb_memory_view_t *view, VALUE obj, void *data, const ssize_t len, const int readonly);
+ssize_t rb_memory_view_parse_item_format(const char *format,
+                                         rb_memory_view_item_component_t **members,
+                                         ssize_t *n_members, const char **err);
+ssize_t rb_memory_view_item_size_from_format(const char *format, const char **err);
+void *rb_memory_view_get_item_pointer(rb_memory_view_t *view, const ssize_t *indices);
+
+int rb_memory_view_available_p(VALUE obj);
+int rb_memory_view_get(VALUE obj, rb_memory_view_t* memory_view, int flags);
+int rb_memory_view_release(rb_memory_view_t* memory_view);
+
+RBIMPL_SYMBOL_EXPORT_END()
+
+#endif /* RUBY_BUFFER_H */