From 063e0c98b83abd13b377d27e82267fb9a7a89680 Mon Sep 17 00:00:00 2001
From: Jacek Sieka <jacek@status.im>
Date: Thu, 14 Apr 2022 21:57:11 +0200
Subject: [PATCH] avoid zeroMem when resizing trivial seq:s

might as well grab a new sequence instead
---
 stew/assign2.nim | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/stew/assign2.nim b/stew/assign2.nim
index 5e34cf9..ecf0582 100644
--- a/stew/assign2.nim
+++ b/stew/assign2.nim
@@ -32,7 +32,14 @@ func assign*[T](tgt: var openArray[T], src: openArray[T]) =
 func assign*[T](tgt: var seq[T], src: openArray[T]) =
   mixin assign
 
-  tgt.setLen(src.len)
+  when T is SomeNumber:
+    # `setLen` does costly zero:ing both when growing _and_ shrinking
+    if tgt.len > src.len or tgt.len < src.len div 4:
+      tgt = newSeqUninitialized[T](src.len)
+    else:
+      tgt.setLen(src.len)
+  else:
+    tgt.setLen(src.len)
   assignImpl(tgt.toOpenArray(0, tgt.high), src)
 
 func assign*(tgt: var string, src: string) =