fix: base64DecodeBytes unsigned byte values + improve JMH benchmark config

bench/src/sjsonnet/bench/RegressionBenchmark.scala

@@ -23,8 +23,8 @@ object RegressionBenchmark {
 
 @BenchmarkMode(Array(Mode.AverageTime))
 @Fork(1)
-@Warmup(iterations = 1, time = 2)
-@Measurement(iterations = 1)
+@Warmup(iterations = 3, time = 2)
+@Measurement(iterations = 3)
 @OutputTimeUnit(TimeUnit.MILLISECONDS)
 @State(Scope.Benchmark)
 class RegressionBenchmark {

sjsonnet/src/sjsonnet/stdlib/EncodingModule.scala

@@ -50,7 +50,16 @@ object EncodingModule extends AbstractFunctionModule {
     },
     builtin("base64DecodeBytes", "str") { (pos, _, str: String) =>
       try {
-        Val.Arr(pos, Base64.getDecoder.decode(str).map(i => Val.Num(pos, i)))
+        val decoded = Base64.getDecoder.decode(str)
+        val result = new Array[Eval](decoded.length)
+        var i = 0
+        while (i < decoded.length) {
+          // Mask with 0xff to convert signed Java byte (-128..127) to unsigned int (0..255),
+          // matching the Jsonnet specification that byte values are in the range 0-255.
+          result(i) = Val.Num(pos, decoded(i) & 0xff)
+          i += 1
+        }
+        Val.Arr(pos, result)
       } catch {
         case e: IllegalArgumentException =>
           Error.fail("Invalid base64 string: " + e.getMessage)

sjsonnet/test/resources/new_test_suite/base64DecodeBytes_unsigned.jsonnet

@@ -0,0 +1,21 @@
+// Regression test: base64DecodeBytes must return unsigned byte values (0-255).
+// Java's byte type is signed (-128..127), so without masking with 0xff,
+// bytes >= 128 would appear as negative numbers.
+local bytes = std.base64DecodeBytes("gIA=");  // decodes to [0x80, 0x80] = [128, 128]
+
+std.assertEqual(bytes[0], 128) &&
+std.assertEqual(bytes[1], 128) &&
+
+// Test full range: 0xFF = 255
+local highByte = std.base64DecodeBytes("/w==");  // decodes to [0xFF] = [255]
+std.assertEqual(highByte[0], 255) &&
+
+// Test zero byte
+local zeroByte = std.base64DecodeBytes("AA==");  // decodes to [0x00] = [0]
+std.assertEqual(zeroByte[0], 0) &&
+
+// Round-trip test: encode then decode should preserve all byte values including high bytes
+local mixed = [0, 127, 128, 200, 255];
+std.assertEqual(std.base64DecodeBytes(std.base64(mixed)), mixed) &&
+
+true

sjsonnet/test/resources/new_test_suite/base64DecodeBytes_unsigned.jsonnet.golden

@@ -0,0 +1 @@
+true