Convert StructLayoutBuilder to ruby, and allow packing to take an optional packing boundary

1 files changed, 113 insertions, 0 deletions

diff --git a/lib/ffi/struct_layout_builder.rb b/lib/ffi/struct_layout_builder.rb
new file mode 100644
index 0000000..f6e7b14
--- /dev/null
+++ b/lib/ffi/struct_layout_builder.rb
@@ -0,0 +1,113 @@
+
+module FFI
+  class StructLayoutBuilder
+    attr_reader :size, :alignment
+    
+    def initialize
+      @size = 0
+      @alignment = 1
+      @min_alignment = 1
+      @packed = false
+      @union = false
+      @field_names = Array.new
+      @field_map = Hash.new
+    end
+
+    def size=(size)
+      @size = size if size > @size
+    end
+
+    def alignment=(align)
+      @alignment = align if align > @alignment
+      @min_alignment = align
+    end
+
+    def union=(is_union)
+      @union = is_union
+    end
+
+    def union?
+      @union
+    end
+
+    def packed=(packed)
+      if packed.is_a?(Fixnum)
+        @alignment = packed
+        @packed = packed
+      else
+        @packed = packed ? 1 : 0
+      end
+    end
+
+
+    def add_field(name, type, offset = nil)
+
+      if offset.nil? || offset == -1
+        offset = @union ? 0 : align(@size, @packed ? @packed : [ @min_alignment, type.alignment ].max)
+      end
+
+      #
+      # If a FFI::Type type was passed in as the field arg, try and convert to a StructLayout::Field instance
+      #
+      field = if !type.is_a?(StructLayout::Field)
+
+        field_class = if type.is_a?(FFI::Type::Function)
+          StructLayout::Function
+
+        elsif type.is_a?(FFI::Type::Struct)
+          StructLayout::InlineStruct
+
+        elsif type.is_a?(FFI::Type::Array)
+          StructLayout::Array
+
+        elsif type.is_a?(FFI::Enum)
+          StructLayout::Enum
+
+        elsif type.is_a?(FFI::Type)
+          StructLayout::Field
+        else
+          raise TypeError, "invalid struct field type #{type.inspect}" unless field_class
+        end
+
+        field_class.new(name, offset, type)
+
+      else
+        type
+      end
+
+      store_field(name, field, type)
+      
+    end
+
+    def add_struct(name, type, offset = nil)
+      add_field(name, FFI::Type::Struct.new(type), offset)
+    end
+
+    def add_array(name, type, count, offset = nil)
+      add_field(name, FFI::Type::Array.new(type, count), offset)
+    end
+
+    def build
+      # Add tail padding if the struct is not packed
+      size = @packed ? @size : align(@size, @alignment)
+      
+      FFI::StructLayout.new(@field_names, @field_map, size, @alignment)
+    end
+
+    private
+    
+    def align(offset, align)
+      align + ((offset - 1) & ~(align - 1));
+    end
+
+
+    def store_field(name, field, type)
+      @field_names << name
+      @field_map[name] = field
+      @alignment = @packed ? @packed : [ @alignment, type.alignment ].max
+      @size = [ @size, type.size + (@union ? 0 : field.offset) ].max
+    end
+
+  end
+
+end
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