small perf improvements on workerd/api

src/workerd/api/data-url.c++

@@ -1,5 +1,6 @@
 #include "data-url.h"
 #include <kj/encoding.h>
+#include <array>
 
 namespace workerd::api {
 
@@ -21,12 +22,16 @@ kj::Maybe<DataUrl> DataUrl::from(const jsg::Url& url) {
   // Per the fetch spec, it doesn't matter if the comma is within a quoted
   // string value in the MIME type... which is fun.
 
-  static const auto isAsciiWhitespace = [](auto c) {
-    return c == 0x09 /* tab */ ||
-          c == 0x0a /* lf  */ ||
-          c == 0x0c /* ff  */ ||
-          c == 0x0d /* cr  */ ||
-          c == 0x20 /* sp  */;
+  static constexpr std::array<uint8_t, 256> ascii_whitespace_table = []() consteval {
+    std::array<uint8_t, 256> result{};
+    for (uint8_t c : { 0x09, 0x0a, 0x0c, 0x0d, 0x20 }) {
+      result[c] = true;
+    }
+    return result;
+  }();
+
+  static constexpr auto isAsciiWhitespace = [](uint8_t c) {
+    return ascii_whitespace_table[c];
   };
 
   static const auto trim = [](auto label) {

src/workerd/api/form-data.c++

@@ -84,11 +84,11 @@ void parseFormData(kj::Maybe<jsg::Lock&> js, kj::Vector<FormData::Entry>& data,
   const auto done = [](kj::ArrayPtr<const char>& body) {
     // Consume any (CR)LF characters that trailed the boundary and indicate continuation, or consume
     // the terminal "--" characters and indicate termination, or throw an error.
-    if (startsWith(body, "\n")) {
+    if (startsWith(body, "\n"_kj)) {
       body = body.slice(1, body.size());
-    } else if (startsWith(body, "\r\n")) {
+    } else if (startsWith(body, "\r\n"_kj)) {
       body = body.slice(2, body.size());
-    } else if (startsWith(body, "--")) {
+    } else if (startsWith(body, "--"_kj)) {
       // We're done!
       return true;
     } else {