From 64ec09d155efbb03b878f0891ac3a8694e0b01ea Mon Sep 17 00:00:00 2001
From: Steve Bennett <steveb@workware.net.au>
Date: Sat, 6 Jun 2020 19:31:35 +1000
Subject: [PATCH] core: improve the performance of lists

Under some circumstances, such as lrepeat and lreverse we know
the length of the final list, so allocate the final size immediately
rather than growing the table in multiple steps.

Signed-off-by: Steve Bennett <steveb@workware.net.au>
---
 jim.c | 39 +++++++++++++++++++++++++--------------
 1 file changed, 25 insertions(+), 14 deletions(-)

diff --git a/jim.c b/jim.c
index 71d6de1..521f25e 100644
--- a/jim.c
+++ b/jim.c
@@ -6867,6 +6867,22 @@ static int ListSortElements(Jim_Interp *interp, Jim_Obj *listObjPtr, struct lsor
     return rc;
 }
 
+/* Ensure there is room for at least 'idx' values in the list */
+static void ListEnsureLength(Jim_Obj *listPtr, int idx)
+{
+    assert(idx >= 0);
+    if (idx >= listPtr->internalRep.listValue.maxLen) {
+        if (idx < 4) {
+            /* Don't do allocations of under 4 pointers. */
+            idx = 4;
+        }
+        listPtr->internalRep.listValue.ele = Jim_Realloc(listPtr->internalRep.listValue.ele,
+            sizeof(Jim_Obj *) * idx);
+
+        listPtr->internalRep.listValue.maxLen = idx;
+    }
+}
+
 /* This is the low-level function to insert elements into a list.
  * The higher-level Jim_ListInsertElements() performs shared object
  * check and invalidates the string repr. This version is used
@@ -6885,18 +6901,11 @@ static void ListInsertElements(Jim_Obj *listPtr, int idx, int elemc, Jim_Obj *co
     Jim_Obj **point;
 
     if (requiredLen > listPtr->internalRep.listValue.maxLen) {
-        if (requiredLen < 2) {
-            /* Don't do allocations of under 4 pointers. */
-            requiredLen = 4;
-        }
-        else {
+        if (currentLen) {
+            /* Assume that we will need extra space for future expansion */
             requiredLen *= 2;
         }
-
-        listPtr->internalRep.listValue.ele = Jim_Realloc(listPtr->internalRep.listValue.ele,
-            sizeof(Jim_Obj *) * requiredLen);
-
-        listPtr->internalRep.listValue.maxLen = requiredLen;
+        ListEnsureLength(listPtr, requiredLen);
     }
     if (idx < 0) {
         idx = currentLen;
@@ -15102,7 +15111,6 @@ static int Jim_LrepeatCoreCommand(Jim_Interp *interp, int argc, Jim_Obj *const *
         Jim_WrongNumArgs(interp, 1, argv, "count ?value ...?");
         return JIM_ERR;
     }
-
     if (count == 0 || argc == 2) {
         return JIM_OK;
     }
@@ -15110,8 +15118,9 @@ static int Jim_LrepeatCoreCommand(Jim_Interp *interp, int argc, Jim_Obj *const *
     argc -= 2;
     argv += 2;
 
-    objPtr = Jim_NewListObj(interp, argv, argc);
-    while (--count) {
+    objPtr = Jim_NewListObj(interp, NULL, 0);
+    ListEnsureLength(objPtr, argc * count);
+    while (count--) {
         ListInsertElements(objPtr, -1, argc, argv);
     }
 
@@ -15214,8 +15223,9 @@ static int Jim_LreverseCoreCommand(Jim_Interp *interp, int argc, Jim_Obj *const
         return JIM_ERR;
     }
     JimListGetElements(interp, argv[1], &len, &ele);
-    len--;
     revObjPtr = Jim_NewListObj(interp, NULL, 0);
+    ListEnsureLength(revObjPtr, len);
+    len--;
     while (len >= 0)
         ListAppendElement(revObjPtr, ele[len--]);
     Jim_SetResult(interp, revObjPtr);
@@ -15275,6 +15285,7 @@ static int Jim_RangeCoreCommand(Jim_Interp *interp, int argc, Jim_Obj *const *ar
         return JIM_ERR;
     }
     objPtr = Jim_NewListObj(interp, NULL, 0);
+    ListEnsureLength(objPtr, len);
     for (i = 0; i < len; i++)
         ListAppendElement(objPtr, Jim_NewIntObj(interp, start + i * step));
     Jim_SetResult(interp, objPtr);
-- 
2.11.4.GIT