diff --git a/bench/resources/jdk17_suite/hash.jsonnet b/bench/resources/jdk17_suite/hash.jsonnet
new file mode 100644
index 00000000..f22881c2
--- /dev/null
+++ b/bench/resources/jdk17_suite/hash.jsonnet
@@ -0,0 +1,15 @@
+local seed = 'sjsonnet-π-你好-🙂';
+local payload = std.repeat(seed, 4096);
+
+[
+  std.md5(payload),
+  std.sha1(payload),
+  std.sha256(payload),
+  std.sha512(payload),
+  std.sha3(payload),
+  std.md5(payload + 'x'),
+  std.sha1(payload + 'x'),
+  std.sha256(payload + 'x'),
+  std.sha512(payload + 'x'),
+  std.sha3(payload + 'x'),
+]
diff --git a/bench/resources/jdk17_suite/hash.jsonnet.golden b/bench/resources/jdk17_suite/hash.jsonnet.golden
new file mode 100644
index 00000000..7837ad1a
--- /dev/null
+++ b/bench/resources/jdk17_suite/hash.jsonnet.golden
@@ -0,0 +1,12 @@
+[
+   "165bc8753a6c3602e01e93e67f446dc1",
+   "03d65852d06704e568d463980671b2f83258a631",
+   "079fd3c2592dc4c9e33e9ac4ddfd3b718f7fa3967ce2c665e6cc1ca7f7ae59bb",
+   "a7c354161415d600561ebcd0ba827d2ed47e5a3b17505e67ce9f367841d586e67c983212d9f9e38c3d54e2fe8cc9c657204b138a15a714909afe8f33064cd518",
+   "6746867e50f7e0bf298dfec41831460c638827a57243d13d5ce240e362dee95b603abbaf4b0d3be2df447ecd773ba1bc3560049afea9b32493ead77b72002ac8",
+   "3d176bc0962944b43e15dfc5a23423d5",
+   "fade71afb8da391b3e2fe225817f88b1929c463f",
+   "b3eca3625fccdb13bb8fade19a9d7557a24163c7cf5ba8b60013d612074a9328",
+   "c5811f7c6e4c0b75b721212b58dfb567b5ecdf93f940308b51b33a9937d7c47548dee504999285a636600cfb2f22d3794afb856732ca7268c775cabdf81bda5e",
+   "3aacea0bd0120dcae41c98ecbcef3d9f5fa15ebcd25e524a6f183ef5757dea87908298a568b513cde81f036bffe8b88db629d50328eb61605c5b8fdf6958c7e0"
+]
diff --git a/bench/resources/jdk17_suite/repeat_format.jsonnet b/bench/resources/jdk17_suite/repeat_format.jsonnet
new file mode 100644
index 00000000..efffab50
--- /dev/null
+++ b/bench/resources/jdk17_suite/repeat_format.jsonnet
@@ -0,0 +1,19 @@
+local values = std.range(0, 512);
+local words = std.makeArray(128, function(i) 'w' + i);
+local repeated = std.repeat('ab', 4096);
+local decimal = std.join('|', ['%08d' % v for v in values]);
+local hex = std.join('|', ['%010x' % v for v in values]);
+local left = std.join('|', ['%-20s' % w for w in words]);
+local right = std.join('|', ['%20s' % w for w in words]);
+
+{
+  repeatedLen: std.length(repeated),
+  decimalLen: std.length(decimal),
+  decimalTail: std.substr(decimal, std.length(decimal) - 8, 8),
+  hexLen: std.length(hex),
+  hexTail: std.substr(hex, std.length(hex) - 10, 10),
+  leftLen: std.length(left),
+  leftTail: std.substr(left, std.length(left) - 20, 20),
+  rightLen: std.length(right),
+  rightTail: std.substr(right, std.length(right) - 20, 20),
+}
diff --git a/bench/resources/jdk17_suite/repeat_format.jsonnet.golden b/bench/resources/jdk17_suite/repeat_format.jsonnet.golden
new file mode 100644
index 00000000..588251b1
--- /dev/null
+++ b/bench/resources/jdk17_suite/repeat_format.jsonnet.golden
@@ -0,0 +1,11 @@
+{
+   "decimalLen": 4616,
+   "decimalTail": "00000512",
+   "hexLen": 5642,
+   "hexTail": "0000000200",
+   "leftLen": 2687,
+   "leftTail": "w127                ",
+   "repeatedLen": 8192,
+   "rightLen": 2687,
+   "rightTail": "                w127"
+}
diff --git a/bench/resources/jdk17_suite/split_resolve.jsonnet b/bench/resources/jdk17_suite/split_resolve.jsonnet
new file mode 100644
index 00000000..4cf8047f
--- /dev/null
+++ b/bench/resources/jdk17_suite/split_resolve.jsonnet
@@ -0,0 +1,18 @@
+local parts = std.makeArray(512, function(i) 'segment' + i);
+local joined = std.join('::', parts);
+local files = std.makeArray(512, function(i) 'a/b/c/file' + i + '.jsonnet');
+local split = std.split(joined, '::');
+local splitLimit = std.splitLimit(joined, '::', 128);
+local splitLimitR = std.splitLimitR(joined, '::', 128);
+local resolved = std.join('|', [std.resolvePath(f, 'libsonnet/main.libsonnet') for f in files]);
+
+{
+  splitLen: std.length(split),
+  splitJoinLen: std.length(std.join('', split)),
+  splitLimitLen: std.length(splitLimit),
+  splitLimitLastLen: std.length(splitLimit[128]),
+  splitLimitRLen: std.length(splitLimitR),
+  splitLimitRFirstLen: std.length(splitLimitR[0]),
+  resolveLen: std.length(resolved),
+  resolveTail: std.substr(resolved, std.length(resolved) - 30, 30),
+}
diff --git a/bench/resources/jdk17_suite/split_resolve.jsonnet.golden b/bench/resources/jdk17_suite/split_resolve.jsonnet.golden
new file mode 100644
index 00000000..fe300b11
--- /dev/null
+++ b/bench/resources/jdk17_suite/split_resolve.jsonnet.golden
@@ -0,0 +1,10 @@
+{
+   "resolveLen": 15871,
+   "resolveTail": "a/b/c/libsonnet/main.libsonnet",
+   "splitJoinLen": 5010,
+   "splitLen": 512,
+   "splitLimitLastLen": 4606,
+   "splitLimitLen": 129,
+   "splitLimitRFirstLen": 4496,
+   "splitLimitRLen": 129
+}
diff --git a/build.mill b/build.mill
index 3eb2b60a..58350b72 100644
--- a/build.mill
+++ b/build.mill
@@ -111,6 +111,7 @@ object bench extends ScalaModule with JmhModule with ScalafmtModule {
     this.moduleDir / "resources" / "bug_suite",
     this.moduleDir / "resources" / "cpp_suite",
     this.moduleDir / "resources" / "go_suite",
+    this.moduleDir / "resources" / "jdk17_suite",
     this.moduleDir / "resources" / "sjsonnet_suite"
   )
 
diff --git a/sjsonnet/src-js/sjsonnet/Platform.scala b/sjsonnet/src-js/sjsonnet/Platform.scala
index 22cfb9f0..e35a79e2 100644
--- a/sjsonnet/src-js/sjsonnet/Platform.scala
+++ b/sjsonnet/src-js/sjsonnet/Platform.scala
@@ -7,6 +7,22 @@ import java.util.regex.Pattern
 import scala.collection.mutable
 
 object Platform {
+  private def repeatCapacity(s: String, count: Int): Int =
+    if (count > 0 && s.length <= Int.MaxValue / count) s.length * count else 0
+
+  def repeatString(s: String, count: Int): String = {
+    if (count <= 0 || s.isEmpty) ""
+    else {
+      val builder = new StringBuilder(repeatCapacity(s, count))
+      var i = 0
+      while (i < count) {
+        builder.append(s)
+        i += 1
+      }
+      builder.toString()
+    }
+  }
+
   private def nodeToJson(node: Node): ujson.Value = node match {
     case _: Node.ScalarNode =>
       YamlDecoder.forAny.construct(node).getOrElse("") match {
diff --git a/sjsonnet/src-jvm-native/sjsonnet/SjsonnetMainBase.scala b/sjsonnet/src-jvm-native/sjsonnet/SjsonnetMainBase.scala
index 21cd1703..ad31d4c5 100644
--- a/sjsonnet/src-jvm-native/sjsonnet/SjsonnetMainBase.scala
+++ b/sjsonnet/src-jvm-native/sjsonnet/SjsonnetMainBase.scala
@@ -353,10 +353,10 @@ object SjsonnetMainBase {
       codeFiles: Seq[String],
       wd: os.Path): Map[String, String] = {
 
-    def split(s: String) = s.split("=", 2) match {
-      case Array(x)    => (x, System.getenv(x))
-      case Array(x, v) => (x, v)
-      case _           => throw new IllegalArgumentException("invalid binding: " + s)
+    def split(s: String) = {
+      val idx = s.indexOf('=')
+      if (idx < 0) (s, System.getenv(s))
+      else (s.substring(0, idx), s.substring(idx + 1))
     }
 
     def splitMap(s: Seq[String], f: String => String) =
diff --git a/sjsonnet/src-jvm/sjsonnet/Platform.scala b/sjsonnet/src-jvm/sjsonnet/Platform.scala
index 2bc28595..db6e81b7 100644
--- a/sjsonnet/src-jvm/sjsonnet/Platform.scala
+++ b/sjsonnet/src-jvm/sjsonnet/Platform.scala
@@ -1,8 +1,10 @@
 package sjsonnet
 
 import java.io.{BufferedInputStream, ByteArrayOutputStream, File, FileInputStream}
+import java.nio.charset.StandardCharsets.UTF_8
 import java.util
 import java.util.Base64
+import java.util.HexFormat
 import java.util.zip.GZIPOutputStream
 import com.google.re2j.Pattern
 import net.jpountz.xxhash.{StreamingXXHash64, XXHashFactory}
@@ -16,6 +18,11 @@ import scala.collection.mutable
 import scala.jdk.CollectionConverters.*
 
 object Platform {
+  private val hexFormat = HexFormat.of()
+
+  def repeatString(s: String, count: Int): String =
+    if (count <= 0) "" else s.repeat(count)
+
   def gzipBytes(b: Array[Byte]): String = {
     val outputStream: ByteArrayOutputStream = new ByteArrayOutputStream(b.length)
     val gzip: GZIPOutputStream = new GZIPOutputStream(outputStream)
@@ -29,7 +36,7 @@ object Platform {
   }
 
   def gzipString(s: String): String = {
-    gzipBytes(s.getBytes())
+    gzipBytes(s.getBytes(UTF_8))
   }
 
   /**
@@ -50,7 +57,7 @@ object Platform {
   }
 
   def xzString(s: String, compressionLevel: Option[Int]): String = {
-    xzBytes(s.getBytes(), compressionLevel)
+    xzBytes(s.getBytes(UTF_8), compressionLevel)
   }
 
   private def nodeToJson(node: Any): ujson.Value = node match {
@@ -105,13 +112,10 @@ object Platform {
     }
   }
 
-  private def computeHash(algorithm: String, s: String) = {
-    java.security.MessageDigest
-      .getInstance(algorithm)
-      .digest(s.getBytes("UTF-8"))
-      .map { b => String.format("%02x", (b & 0xff).asInstanceOf[Integer]) }
-      .mkString
-  }
+  private def computeHash(algorithm: String, s: String): String =
+    hexFormat.formatHex(
+      java.security.MessageDigest.getInstance(algorithm).digest(s.getBytes(UTF_8))
+    )
 
   def md5(s: String): String = computeHash("MD5", s)
 
diff --git a/sjsonnet/src-native/sjsonnet/Platform.scala b/sjsonnet/src-native/sjsonnet/Platform.scala
index 8ea3be50..26179bb1 100644
--- a/sjsonnet/src-native/sjsonnet/Platform.scala
+++ b/sjsonnet/src-native/sjsonnet/Platform.scala
@@ -1,6 +1,7 @@
 package sjsonnet
 
 import java.io.{ByteArrayOutputStream, File}
+import java.nio.charset.StandardCharsets.UTF_8
 import java.util
 import java.util.Base64
 import java.util.zip.GZIPOutputStream
@@ -9,6 +10,24 @@ import scala.collection.mutable
 import org.virtuslab.yaml.*
 
 object Platform {
+  private val hexChars = "0123456789abcdef".toCharArray
+
+  private def repeatCapacity(s: String, count: Int): Int =
+    if (count > 0 && s.length <= Int.MaxValue / count) s.length * count else 0
+
+  def repeatString(s: String, count: Int): String = {
+    if (count <= 0 || s.isEmpty) ""
+    else {
+      val builder = new StringBuilder(repeatCapacity(s, count))
+      var i = 0
+      while (i < count) {
+        builder.append(s)
+        i += 1
+      }
+      builder.toString()
+    }
+  }
+
   def gzipBytes(b: Array[Byte]): String = {
     val outputStream: ByteArrayOutputStream = new ByteArrayOutputStream(b.length)
     val gzip: GZIPOutputStream = new GZIPOutputStream(outputStream)
@@ -22,7 +41,7 @@ object Platform {
   }
 
   def gzipString(s: String): String = {
-    gzipBytes(s.getBytes())
+    gzipBytes(s.getBytes(UTF_8))
   }
 
   def xzBytes(s: Array[Byte], compressionLevel: Option[Int]): String = {
@@ -140,14 +159,23 @@ object Platform {
     result.mkString("\n")
   }
 
-  private def computeHash(algorithm: String, s: String) = {
-    java.security.MessageDigest
-      .getInstance(algorithm)
-      .digest(s.getBytes("UTF-8"))
-      .map { b => String.format("%02x", (b & 0xff).asInstanceOf[Integer]) }
-      .mkString
+  private def bytesToHex(bytes: Array[Byte]): String = {
+    val out = new Array[Char](bytes.length * 2)
+    var i = 0
+    var j = 0
+    while (i < bytes.length) {
+      val b = bytes(i) & 0xff
+      out(j) = hexChars(b >>> 4)
+      out(j + 1) = hexChars(b & 0x0f)
+      i += 1
+      j += 2
+    }
+    new String(out)
   }
 
+  private def computeHash(algorithm: String, s: String): String =
+    bytesToHex(java.security.MessageDigest.getInstance(algorithm).digest(s.getBytes(UTF_8)))
+
   def md5(s: String): String = computeHash("MD5", s)
 
   def sha1(s: String): String = computeHash("SHA-1", s)
diff --git a/sjsonnet/src/sjsonnet/DecimalFormat.scala b/sjsonnet/src/sjsonnet/DecimalFormat.scala
index c8760427..112555f5 100644
--- a/sjsonnet/src/sjsonnet/DecimalFormat.scala
+++ b/sjsonnet/src/sjsonnet/DecimalFormat.scala
@@ -23,7 +23,7 @@ object DecimalFormat {
     val sign = if (n < 0) "-" else ""
     val absN = math.abs(n)
     val nWidth = if (absN == 0) 1 else Math.log10(absN.toDouble).toInt + 1
-    sign + "0" * (targetWidth - nWidth) + absN
+    sign + Platform.repeatString("0", targetWidth - nWidth) + absN
   }
 
   private def rightPad(n0: Long, minWidth: Int, maxWidth: Int): String = {
@@ -32,7 +32,7 @@ object DecimalFormat {
       val n = (n0 / Math.pow(10, trailingZeroes(n0))).toInt
       assert(n == math.abs(n))
       val nWidth = if (n == 0) 1 else Math.log10(n).toInt + 1
-      ("" + n + "0" * (minWidth - nWidth)).take(maxWidth)
+      ("" + n + Platform.repeatString("0", minWidth - nWidth)).take(maxWidth)
     }
   }
 
diff --git a/sjsonnet/src/sjsonnet/Format.scala b/sjsonnet/src/sjsonnet/Format.scala
index 8d83afa1..212e2600 100644
--- a/sjsonnet/src/sjsonnet/Format.scala
+++ b/sjsonnet/src/sjsonnet/Format.scala
@@ -254,14 +254,14 @@ object Format {
       if (lhs2.isEmpty && mhs.isEmpty) rhs
       else if (lhs2.isEmpty) mhs + rhs
       else lhs2 + mhs + rhs
-    } else if (formatted.zeroPadded) {
-      if (numeric) lhs2 + mhs + "0" * missingWidth + rhs
-      else {
-        if (formatted.leftAdjusted) lhs2 + mhs + rhs + " " * missingWidth
-        else " " * missingWidth + lhs2 + mhs + rhs
-      }
-    } else if (formatted.leftAdjusted) lhs2 + mhs + rhs + " " * missingWidth
-    else " " * missingWidth + lhs2 + mhs + rhs
+    } else {
+      val padding =
+        if (formatted.zeroPadded && numeric) Platform.repeatString("0", missingWidth)
+        else Platform.repeatString(" ", missingWidth)
+      if (formatted.zeroPadded && numeric) lhs2 + mhs + padding + rhs
+      else if (formatted.leftAdjusted) lhs2 + mhs + rhs + padding
+      else padding + lhs2 + mhs + rhs
+    }
   }
 
   def format(s: String, values0: Val, pos: Position)(implicit evaluator: EvalScope): String = {
@@ -929,7 +929,7 @@ object Format {
     if (precision == FormatSpec.NoNumber) rhs
     else {
       val shortage = precision - rhs.length
-      if (shortage > 0) "0" * shortage + rhs else rhs
+      if (shortage > 0) Platform.repeatString("0", shortage) + rhs else rhs
     }
   }
 
diff --git a/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala b/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala
index 1f578996..5e06a7a0 100644
--- a/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala
+++ b/sjsonnet/src/sjsonnet/stdlib/ArrayModule.scala
@@ -861,13 +861,7 @@ object ArrayModule extends AbstractFunctionModule {
       }
       val res: Val = what match {
         case Val.Str(_, str) =>
-          val builder = new StringBuilder(str.length * count)
-          var i = 0
-          while (i < count) {
-            builder.append(str)
-            i += 1
-          }
-          Val.Str(pos, builder.toString())
+          Val.Str(pos, Platform.repeatString(str, count))
         case a: Val.Arr =>
           if (a.length.toLong * count.toLong > Int.MaxValue)
             Error.fail("array too large", pos)(ev)
diff --git a/sjsonnet/src/sjsonnet/stdlib/EncodingModule.scala b/sjsonnet/src/sjsonnet/stdlib/EncodingModule.scala
index f2375440..f6545648 100644
--- a/sjsonnet/src/sjsonnet/stdlib/EncodingModule.scala
+++ b/sjsonnet/src/sjsonnet/stdlib/EncodingModule.scala
@@ -5,8 +5,6 @@ import java.nio.charset.StandardCharsets.UTF_8
 import sjsonnet._
 import sjsonnet.functions.AbstractFunctionModule
 
-import java.nio.charset.StandardCharsets.UTF_8
-
 /**
  * Native implementations for Jsonnet standard-library entries in this module.
  *
diff --git a/sjsonnet/src/sjsonnet/stdlib/StringModule.scala b/sjsonnet/src/sjsonnet/stdlib/StringModule.scala
index defd7b19..707d2c72 100644
--- a/sjsonnet/src/sjsonnet/stdlib/StringModule.scala
+++ b/sjsonnet/src/sjsonnet/stdlib/StringModule.scala
@@ -465,21 +465,16 @@ object StringModule extends AbstractFunctionModule {
     val b = new mutable.ArrayBuilder.ofRef[Eval]
     if (maxSplits >= 0 && maxSplits < Int.MaxValue) b.sizeHint(maxSplits + 1)
     var sz = 0
-    var i = 0
     var start = 0
+    var next = if (maxSplits == 0) -1 else str.indexOf(cStr, start)
 
-    while (i <= str.length - cStr.length && (maxSplits < 0 || sz < maxSplits)) {
-      if (str.startsWith(cStr, i)) {
-        val finalStr = Val.Str(pos, str.substring(start, i))
-        b.+=(finalStr)
-        start = i + cStr.length
-        sz += 1
-        i += cStr.length
-      } else {
-        i += 1
-      }
+    while (next >= 0 && (maxSplits < 0 || sz < maxSplits)) {
+      b += Val.Str(pos, str.substring(start, next))
+      start = next + cStr.length
+      sz += 1
+      next = if (maxSplits >= 0 && sz >= maxSplits) -1 else str.indexOf(cStr, start)
     }
-    b.+=(Val.Str(pos, str.substring(start)))
+    b += Val.Str(pos, str.substring(start))
     sz += 1
     b.result()
   }
@@ -787,21 +782,9 @@ object StringModule extends AbstractFunctionModule {
     builtin(SplitLimit),
     builtin(SplitLimitR),
     builtin("resolvePath", "f", "r") { (_, _, f: String, r: String) =>
-      val parts = f.split("/", -1)
-      val prefixCount = parts.length - 1
-      if (prefixCount <= 0) r
-      else {
-        val out = new java.lang.StringBuilder(f.length + r.length)
-        var i = 0
-        while (i < prefixCount) {
-          if (i > 0) out.append('/')
-          out.append(parts(i))
-          i += 1
-        }
-        out.append('/')
-        out.append(r)
-        out.toString
-      }
+      val slash = f.lastIndexOf('/')
+      if (slash < 0) r
+      else f.substring(0, slash + 1) + r
     },
     builtin(StringChars),
     builtin(ParseInt),
diff --git a/sjsonnet/test/resources/new_test_suite/jdk17_hash_directional-jvm.jsonnet b/sjsonnet/test/resources/new_test_suite/jdk17_hash_directional-jvm.jsonnet
new file mode 100644
index 00000000..2125bd14
--- /dev/null
+++ b/sjsonnet/test/resources/new_test_suite/jdk17_hash_directional-jvm.jsonnet
@@ -0,0 +1,5 @@
+// JVM/Native-only directional hash vectors. Scala.js intentionally does not implement these APIs.
+
+local s = "sjsonnet-π-你好-🙂";
+
+std.assertEqual(std.sha256(s), "d42b7a53590c05dc117ea4cfc8dd0a52670e125ee505dc9a280205081a560d84")
diff --git a/sjsonnet/test/resources/new_test_suite/jdk17_hash_directional-jvm.jsonnet.golden b/sjsonnet/test/resources/new_test_suite/jdk17_hash_directional-jvm.jsonnet.golden
new file mode 100644
index 00000000..27ba77dd
--- /dev/null
+++ b/sjsonnet/test/resources/new_test_suite/jdk17_hash_directional-jvm.jsonnet.golden
@@ -0,0 +1 @@
+true
diff --git a/sjsonnet/test/resources/new_test_suite/jdk17_shared_directional.jsonnet b/sjsonnet/test/resources/new_test_suite/jdk17_shared_directional.jsonnet
new file mode 100644
index 00000000..d4d0cbdd
--- /dev/null
+++ b/sjsonnet/test/resources/new_test_suite/jdk17_shared_directional.jsonnet
@@ -0,0 +1,14 @@
+// Directional tests for platform-specialized string helpers.
+// These assert exact outputs, not only roundtrips, so consistently-wrong implementations fail.
+
+std.assertEqual(std.repeat("é", 3), "ééé") &&
+
+std.assertEqual("%-5s" % "x", "x    ") &&
+std.assertEqual("%010x" % 255, "00000000ff") &&
+
+std.assertEqual(std.split("a::::b::", "::"), ["a", "", "b", ""]) &&
+std.assertEqual(std.split("aaaa", "aa"), ["", "", ""]) &&
+std.assertEqual(std.splitLimit("a::b::c", "::", 0), ["a::b::c"]) &&
+std.assertEqual(std.splitLimitR("a::b::c", "::", 1), ["a::b", "c"]) &&
+
+std.assertEqual(std.resolvePath("a/b/", "d.libsonnet"), "a/b/d.libsonnet")
diff --git a/sjsonnet/test/resources/new_test_suite/jdk17_shared_directional.jsonnet.golden b/sjsonnet/test/resources/new_test_suite/jdk17_shared_directional.jsonnet.golden
new file mode 100644
index 00000000..27ba77dd
--- /dev/null
+++ b/sjsonnet/test/resources/new_test_suite/jdk17_shared_directional.jsonnet.golden
@@ -0,0 +1 @@
+true