memory_view.c: Add rb_memory_view_get_item and rb_memory_view_prepare…

…_item_desc (#3871)

ext/-test-/memory_view/memory_view.c

@@ -264,9 +264,17 @@ static int
 mdview_get_memory_view(VALUE obj, rb_memory_view_t *view, int flags)
 {
     VALUE buf_v = rb_ivar_get(obj, id_str);
+    VALUE format_v = rb_ivar_get(obj, SYM2ID(sym_format));
     VALUE shape_v = rb_ivar_get(obj, SYM2ID(sym_shape));
     VALUE strides_v = rb_ivar_get(obj, SYM2ID(sym_strides));
 
+    const char *format = RSTRING_PTR(format_v);
+    const char *err;
+    const ssize_t item_size = rb_memory_view_item_size_from_format(format, &err);
+    if (item_size < 0) {
+        return 0;
+    }
+
     ssize_t i, ndim = RARRAY_LEN(shape_v);
     ssize_t *shape = ALLOC_N(ssize_t, ndim);
     ssize_t *strides = NULL;
@@ -288,8 +296,8 @@ mdview_get_memory_view(VALUE obj, rb_memory_view_t *view, int flags)
     }
 
     rb_memory_view_init_as_byte_array(view, obj, RSTRING_PTR(buf_v), RSTRING_LEN(buf_v), true);
-    view->format = "l";
-    view->item_size = sizeof(long);
+    view->format = StringValueCStr(format_v);
+    view->item_size = item_size;
     view->ndim = ndim;
     view->shape = shape;
     view->strides = strides;
@@ -310,13 +318,15 @@ static const rb_memory_view_entry_t mdview_memory_view_entry = {
 };
 
 static VALUE
-mdview_initialize(VALUE obj, VALUE buf, VALUE shape, VALUE strides)
+mdview_initialize(VALUE obj, VALUE buf, VALUE format, VALUE shape, VALUE strides)
 {
     Check_Type(buf, T_STRING);
+    StringValue(format);
     Check_Type(shape, T_ARRAY);
     if (!NIL_P(strides)) Check_Type(strides, T_ARRAY);
 
     rb_ivar_set(obj, id_str, buf);
+    rb_ivar_set(obj, SYM2ID(sym_format), format);
     rb_ivar_set(obj, SYM2ID(sym_shape), shape);
     rb_ivar_set(obj, SYM2ID(sym_strides), strides);
     return Qnil;
@@ -344,11 +354,8 @@ mdview_aref(VALUE obj, VALUE indices_v)
         indices[i] = NUM2SSIZET(RARRAY_AREF(indices_v, i));
     }
 
-    char *ptr = rb_memory_view_get_item_pointer(&view, indices);
+    VALUE result = rb_memory_view_get_item(&view, indices);
     ALLOCV_END(buf_indices);
-
-    long x = *(long *)ptr;
-    VALUE result = LONG2FIX(x);
     rb_memory_view_release(&view);
 
     return result;
@@ -373,7 +380,7 @@ Init_memory_view(void)
     rb_memory_view_register(cExportableString, &exportable_string_memory_view_entry);
 
     VALUE cMDView = rb_define_class_under(mMemoryViewTestUtils, "MultiDimensionalView", rb_cObject);
-    rb_define_method(cMDView, "initialize", mdview_initialize, 3);
+    rb_define_method(cMDView, "initialize", mdview_initialize, 4);
     rb_define_method(cMDView, "[]", mdview_aref, 1);
     rb_memory_view_register(cMDView, &mdview_memory_view_entry);
 

include/ruby/memory_view.h

@@ -77,11 +77,13 @@ typedef struct {
 
     struct {
         /* The array of rb_memory_view_item_component_t that describes the
-         * item structure. */
+         * item structure.  rb_memory_view_prepare_item_desc and
+         * rb_memory_view_get_item allocate this memory if needed,
+         * and rb_memory_view_release frees it. */
         rb_memory_view_item_component_t *components;
 
         /* The number of components in an item. */
-        ssize_t length;
+        size_t length;
     } item_desc;
 
     /* The number of dimension. */
@@ -132,6 +134,8 @@ ssize_t rb_memory_view_parse_item_format(const char *format,
 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);
 VALUE rb_memory_view_extract_item_members(const void *ptr, const rb_memory_view_item_component_t *members, const size_t n_members);
+VALUE rb_memory_view_prepare_item_dexc(rb_memory_view_t *view);
+VALUE rb_memory_view_get_item(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);

memory_view.c

@@ -226,6 +226,8 @@ rb_memory_view_init_as_byte_array(rb_memory_view_t *view, VALUE obj, void *data,
     view->readonly = readonly;
     view->format = NULL;
     view->item_size = 1;
+    view->item_desc.components = NULL;
+    view->item_desc.length = 0;
     view->ndim = 1;
     view->shape = NULL;
     view->strides = NULL;
@@ -764,6 +766,37 @@ rb_memory_view_extract_item_members(const void *ptr, const rb_memory_view_item_c
     return item;
 }
 
+void
+rb_memory_view_prepare_item_desc(rb_memory_view_t *view)
+{
+    if (view->item_desc.components == NULL) {
+        const char *err;
+        ssize_t n = rb_memory_view_parse_item_format(view->format, &view->item_desc.components, &view->item_desc.length, &err);
+        if (n < 0) {
+            rb_raise(rb_eRuntimeError,
+                     "Unable to parse item format at %"PRIdSIZE" in \"%s\"",
+                     (err - view->format), view->format);
+        }
+    }
+}
+
+/* Return a value that consists of item members in the given memory view. */
+VALUE
+rb_memory_view_get_item(rb_memory_view_t *view, const ssize_t *indices)
+{
+    void *ptr = rb_memory_view_get_item_pointer(view, indices);
+
+    if (view->format == NULL) {
+        return INT2FIX(*(uint8_t *)ptr);
+    }
+
+    if (view->item_desc.components == NULL) {
+        rb_memory_view_prepare_item_desc(view);
+    }
+
+    return rb_memory_view_extract_item_members(ptr, view->item_desc.components, view->item_desc.length);
+}
+
 static const rb_memory_view_entry_t *
 lookup_memory_view_entry(VALUE klass)
 {
@@ -830,6 +863,9 @@ rb_memory_view_release(rb_memory_view_t* view)
         if (rv) {
             unregister_exported_object(view->obj);
             view->obj = Qnil;
+            if (view->item_desc.components) {
+                xfree(view->item_desc.components);
+            }
         }
         return rv;
     }

test/ruby/test_memory_view.rb

@@ -297,25 +297,27 @@ def test_rb_memory_view_fill_contiguous_strides
                  column_major_strides)
   end
 
-  def test_rb_memory_view_get_item_pointer
+  def test_rb_memory_view_get_item_pointer_single_member
     buf = [ 1, 2, 3, 4,
             5, 6, 7, 8,
             9, 10, 11, 12 ].pack("l!*")
     shape = [3, 4]
-    mv = MemoryViewTestUtils::MultiDimensionalView.new(buf, shape, nil)
+    mv = MemoryViewTestUtils::MultiDimensionalView.new(buf, "l!", shape, nil)
     assert_equal(1, mv[[0, 0]])
     assert_equal(4, mv[[0, 3]])
     assert_equal(6, mv[[1, 1]])
     assert_equal(10, mv[[2, 1]])
+  end
 
+  def test_rb_memory_view_get_item_pointer_multiple_members
     buf = [ 1, 2,  3,  4,  5,  6,  7,  8,
-            9, 10, 11, 12, 13, 14, 15, 16 ].pack("l!*")
-    shape = [2, 8]
-    strides = [4*sizeof(:long)*2, sizeof(:long)*2]
-    mv = MemoryViewTestUtils::MultiDimensionalView.new(buf, shape, strides)
-    assert_equal(1, mv[[0, 0]])
-    assert_equal(5, mv[[0, 2]])
-    assert_equal(9, mv[[1, 0]])
-    assert_equal(15, mv[[1, 3]])
+            -1, -2, -3, -4, -5, -6, -7, -8].pack("s*")
+    shape = [2, 4]
+    strides = [4*sizeof(:short)*2, sizeof(:short)*2]
+    mv = MemoryViewTestUtils::MultiDimensionalView.new(buf, "ss", shape, strides)
+    assert_equal([1, 2], mv[[0, 0]])
+    assert_equal([5, 6], mv[[0, 2]])
+    assert_equal([-1, -2], mv[[1, 0]])
+    assert_equal([-7, -8], mv[[1, 3]])
   end
 end