Phase 2E: API Helper Function (lapi.cpp) - Static Function Elimination

Converted 1 static function to lua_State private method:
- reverse() → lua_State::reverseStack()

**Changes**:
- Added 1 private method declaration to lua_State class (lstate.h)
- Added 1 friend function declaration for lua_rotate (public API)
- Converted static function to member method (lapi.cpp)
- Updated 3 call sites in lua_rotate to use L->reverseStack()

**Function Details**:
- reverse() → reverseStack(StkId from, StkId to): Reverses stack elements
  between two positions, used as a building block for lua_rotate's rotation
  algorithm (AB → BA via (A^r · B^r)^r)

**Friend Function** (needs access to API helper):
- lua_rotate() - public API that rotates stack elements, calls reverseStack 3 times

**Call Sites Updated**: 3 call sites in lua_rotate
- Reverse the prefix with length 'n'
- Reverse the suffix
- Reverse the entire segment

**Impact**: Stack manipulation helpers now properly encapsulated as lua_State
private methods. Simple, focused change to a single helper function.

**Files Changed**: 2 files (lstate.h, lapi.cpp)

**Testing**: All tests pass ✅ (2.14s single run)
**Benchmark**: 5-run average = 2.13s ✅ (49% faster than 4.20s baseline!)
**Risk**: LOW (simple helper, single use case, well-tested)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: Peter Neiss

src/core/lapi.cpp

@@ -155,12 +155,12 @@ LUA_API void lua_closeslot (lua_State *L, int idx) {
 ** Note that we move(copy) only the value inside the stack.
 ** (We do not move additional fields that may exist.)
 */
-static void reverse (lua_State *L, StkId from, StkId to) {
+void lua_State::reverseStack(StkId from, StkId to) {
   for (; from < to; from++, to--) {
     TValue temp;
     temp = *s2v(from);
     *s2v(from) = *s2v(to);  /* swap - use operator= */
-    L->getStackSubsystem().setSlot(to, &temp);
+    getStackSubsystem().setSlot(to, &temp);
   }
 }
 
@@ -176,9 +176,9 @@ LUA_API void lua_rotate (lua_State *L, int idx, int n) {
   api_check(L, L->getTbclist().p < segmentStart, "moving a to-be-closed slot");
   api_check(L, (n >= 0 ? n : -n) <= (segmentEnd - segmentStart + 1), "invalid 'n'");
   auto prefixEnd = (n >= 0 ? segmentEnd - n : segmentStart - n - 1);  /* end of prefix */
-  reverse(L, segmentStart, prefixEnd);  /* reverse the prefix with length 'n' */
-  reverse(L, prefixEnd + 1, segmentEnd);  /* reverse the suffix */
-  reverse(L, segmentStart, segmentEnd);  /* reverse the entire segment */
+  L->reverseStack(segmentStart, prefixEnd);  /* reverse the prefix with length 'n' */
+  L->reverseStack(prefixEnd + 1, segmentEnd);  /* reverse the suffix */
+  L->reverseStack(segmentStart, segmentEnd);  /* reverse the entire segment */
   lua_unlock(L);
 }
 

src/core/lstate.h

@@ -754,6 +754,12 @@ struct lua_State : public GCBase<lua_State> {
 
   // Phase 2D: Friend function that needs access to debug private methods
   friend int lua_getinfo(lua_State *L, const char *what, lua_Debug *ar);
+
+  // Phase 2E: API helper (lapi.cpp)
+  void reverseStack(StkId from, StkId to);
+
+  // Phase 2E: Friend function that needs access to API helper
+  friend void lua_rotate(lua_State *L, int idx, int n);
 };