diff --git a/coreblocks/params/instr.py b/coreblocks/params/instr.py
index 6230dc25c..7c12658fc 100644
--- a/coreblocks/params/instr.py
+++ b/coreblocks/params/instr.py
@@ -32,6 +32,26 @@
 
 @dataclass(kw_only=True)
 class Field:
+    """Information about a field in a RISC-V instruction.
+
+    Attributes
+    ----------
+    base: int | list[int]
+        A bit position (or a list of positions) where this field (or parts of the field)
+        would map in the instruction.
+    size: int | list[int]
+        Size (or sizes of the parts) of the field
+    signed: bool
+        Whether this field encodes a signed value.
+    offset: int
+        How many bits of this field should be skipped when encoding the instruction.
+        For example, the immediate of the jump instruction always skips the least
+        significant bit. This only affects encoding procedures, so externally (for example
+        when creating an instance of a instruction) full-size values should be always used.
+    static_value: Optional[Value]
+        Whether the field should have a static value for a given type of an instruction.
+    """
+
     base: int | list[int]
     size: int | list[int]
 
@@ -47,8 +67,8 @@ def bases(self) -> list[int]:
     def sizes(self) -> list[int]:
         return [self.size] if isinstance(self.size, int) else self.size
 
-    def width(self) -> int:
-        return sum(self.sizes())
+    def shape(self) -> Shape:
+        return Shape(width=sum(self.sizes()) + self.offset, signed=self.signed)
 
     def __set_name__(self, owner, name):
         self._name = name
@@ -57,13 +77,13 @@ def __get__(self, obj, objtype=None) -> Value:
         if self.static_value is not None:
             return self.static_value
 
-        return obj.__dict__.get(self._name, C(0, Shape(self.width(), self.signed)))
+        return obj.__dict__.get(self._name, C(0, self.shape()))
 
     def __set__(self, obj, value) -> None:
         if self.static_value is not None:
             raise AttributeError("Can't overwrite the static value of a field.")
 
-        expected_shape = Shape(width=sum(self.sizes()) + self.offset, signed=self.signed)
+        expected_shape = self.shape()
 
         field_val: Value = C(0)
         if isinstance(value, Enum):
@@ -85,6 +105,19 @@ def __set__(self, obj, value) -> None:
         obj.__dict__[self._name] = field_val
 
 
+    def get_parts(self, value: Value) -> list[Value]:
+        base = self.bases()
+        size = self.sizes()
+        offset = self.offset
+
+        ret: list[Value] = []
+        for i in range(len(base)):
+            ret.append(value[offset : offset + size[i]])
+            offset += size[i]
+        
+        return ret
+
+
 def _get_fields(cls: type) -> list[Field]:
     fields = [cls.__dict__[member] for member in vars(cls) if isinstance(cls.__dict__[member], Field)]
     field_ids = set([id(field) for field in fields])
@@ -114,14 +147,7 @@ def as_value(self) -> Value:
 
         for field in _get_fields(type(self)):
             value = field.__get__(self, type(self))
-
-            base = field.bases()
-            size = field.sizes()
-
-            offset = field.offset
-            for i in range(len(base)):
-                parts.append((base[i], value[offset : offset + size[i]]))
-                offset += size[i]
+            parts += zip(field.bases(), field.get_parts(value))
 
         parts.sort()
         return Cat([part[1] for part in parts])