core/irrt: refactor out slice::indices and range::len

nac3core/irrt/irrt/slice.hpp

@@ -7,6 +7,19 @@
 
 namespace
 {
+namespace range
+{
+template <typename T> T len(T start, T stop, T step)
+{
+    // Reference: https://github.com/python/cpython/blob/9dbd12375561a393eaec4b21ee4ac568a407cdb0/Objects/rangeobject.c#L933
+    if (step > 0 && start < stop)
+        return 1 + (stop - 1 - start) / step;
+    else if (step < 0 && start > stop)
+        return 1 + (start - 1 - stop) / (-step);
+    else
+        return 0;
+}
+} // namespace range
 
 /**
  * @brief A Python range.
@@ -22,15 +35,8 @@ template <typename T> struct Range
      */
     template <typename SizeT> T len()
     {
-        // Reference: https://github.com/python/cpython/blob/9dbd12375561a393eaec4b21ee4ac568a407cdb0/Objects/rangeobject.c#L933
         debug_assert(SizeT, step != 0);
-
+        return range::len(start, stop, step);
-        if (step > 0 && start < stop)
-            return 1 + (stop - 1 - start) / step;
-        else if (step < 0 && start > stop)
-            return 1 + (start - 1 - stop) / (-step);
-        else
-            return 0;
     }
 };
 
@@ -75,6 +81,50 @@ template <typename T> T resolve_index_in_length(T length, T index)
         return -1;
     }
 }
+
+/**
+ * @brief Resolve a slice as a range.
+ *
+ * In Python, this would be `range(*slice(start, stop, step).indices(length))`.
+ */
+template <typename T>
+void indices(bool start_defined, T start, bool stop_defined, T stop, bool step_defined, T step, T length,
+             T *range_start, T *range_stop, T *range_step)
+{
+    // Reference: https://github.com/python/cpython/blob/main/Objects/sliceobject.c#L388
+    *range_step = step_defined ? step : 1;
+    bool step_is_negative = *range_step < 0;
+
+    T lower, upper;
+    if (step_is_negative)
+    {
+        lower = -1;
+        upper = length - 1;
+    }
+    else
+    {
+        lower = 0;
+        upper = length;
+    }
+
+    if (start_defined)
+    {
+        *range_start = start < 0 ? max(lower, start + length) : min(upper, start);
+    }
+    else
+    {
+        *range_start = step_is_negative ? upper : lower;
+    }
+
+    if (stop_defined)
+    {
+        *range_stop = stop < 0 ? max(lower, stop + length) : min(upper, stop);
+    }
+    else
+    {
+        *range_stop = step_is_negative ? lower : upper;
+    }
+}
 } // namespace slice
 
 /**
@@ -132,40 +182,8 @@ template <typename T> struct Slice
         debug_assert(SizeT, length >= 0);
 
         Range<T> result;
-
+        slice::indices(start_defined, start, stop_defined, stop, step_defined, step, length, &result.start,
-        result.step = step_defined ? step : 1;
+                       &result.stop, &result.step);
-        bool step_is_negative = result.step < 0;
-
-        T lower, upper;
-        if (step_is_negative)
-        {
-            lower = -1;
-            upper = length - 1;
-        }
-        else
-        {
-            lower = 0;
-            upper = length;
-        }
-
-        if (start_defined)
-        {
-            result.start = start < 0 ? max(lower, start + length) : min(upper, start);
-        }
-        else
-        {
-            result.start = step_is_negative ? upper : lower;
-        }
-
-        if (stop_defined)
-        {
-            result.stop = stop < 0 ? max(lower, stop + length) : min(upper, stop);
-        }
-        else
-        {
-            result.stop = step_is_negative ? lower : upper;
-        }
-
         return result;
     }