From 126b07e3803d1a268621c317d4c73a3b2aa9ba0e Mon Sep 17 00:00:00 2001
From: He-Pin <hepin1989@gmail.com>
Date: Sat, 18 Apr 2026 20:30:47 +0800
Subject: [PATCH] perf: single-pass std.sum/std.avg without intermediate array
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Motivation:
std.sum and std.avg perform three passes over the input array:
forall (validate) → map (allocate intermediate Array[Double]) → sum.

Modification:
Replace with a single while-loop that validates types and accumulates
in one pass. No intermediate array allocation.

Result:
Eliminates O(n) Array[Double] allocation and two redundant iterations
for every std.sum/std.avg call.
---
 .../src/sjsonnet/stdlib/ArrayModule.scala     | 30 ++++++++++++++-----
 1 file changed, 22 insertions(+), 8 deletions(-)

diff --git a/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala b/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala
index 2bf067f5..51780b1b 100644
--- a/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala
+++ b/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala
@@ -736,19 +736,33 @@ object ArrayModule extends AbstractFunctionModule {
       )
     },
     builtin("sum", "arr") { (_, _, arr: Val.Arr) =>
-      if (!arr.forall(_.isInstanceOf[Val.Num])) {
-        Error.fail("Argument must be an array of numbers")
+      val a = arr.asLazyArray
+      var sum = 0.0
+      var i = 0
+      while (i < a.length) {
+        a(i).value match {
+          case n: Val.Num => sum += n.asDouble
+          case x          => Error.fail("std.sum expected number, got " + x.prettyName)
+        }
+        i += 1
       }
-      arr.asLazyArray.map(_.value.asDouble).sum
+      sum
     },
     builtin("avg", "arr") { (_, _, arr: Val.Arr) =>
-      if (!arr.forall(_.isInstanceOf[Val.Num])) {
-        Error.fail("Argument must be an array of numbers")
-      }
-      if (arr.length == 0) {
+      val a = arr.asLazyArray
+      if (a.length == 0) {
         Error.fail("Cannot calculate average of an empty array")
       }
-      arr.asLazyArray.map(_.value.asDouble).sum / arr.length
+      var sum = 0.0
+      var i = 0
+      while (i < a.length) {
+        a(i).value match {
+          case n: Val.Num => sum += n.asDouble
+          case x          => Error.fail("std.avg expected number, got " + x.prettyName)
+        }
+        i += 1
+      }
+      sum / a.length
     }
   )
 }