Micro-optimize base64Decode (#2897)

* Micro-optimize base64Decode

* Update test expectations

1 files changed, 5 insertions, 7 deletions

diff --git a/src/wasm2js.h b/src/wasm2js.h
index 9d3fdd0ec..a904bd0f9 100644
--- a/src/wasm2js.h
+++ b/src/wasm2js.h
@@ -2258,15 +2258,13 @@ void Wasm2JSGlue::emitMemory(
   base64ReverseLookup[47] = 63; // '/'
   /** @noinline Inlining this function would mean expanding the base64 string 4x times in the source code, which Closure seems to be happy to do. */
   function base64DecodeToExistingUint8Array(uint8Array, offset, b64) {
-    var b1, b2, i = 0, j = offset, bLength = b64.length, end = offset + (bLength*3>>2);
-    if (b64[bLength-2] == '=') --end;
-    if (b64[bLength-1] == '=') --end;
-    for (; i < bLength; i += 4, j += 3) {
+    var b1, b2, i = 0, j = offset, bLength = b64.length, end = offset + (bLength*3>>2) - (b64[bLength-2] == '=') - (b64[bLength-1] == '=');
+    for (; i < bLength; i += 4) {
       b1 = base64ReverseLookup[b64.charCodeAt(i+1)];
       b2 = base64ReverseLookup[b64.charCodeAt(i+2)];
-      uint8Array[j] = base64ReverseLookup[b64.charCodeAt(i)] << 2 | b1 >> 4;
-      if (j+1 < end) uint8Array[j+1] = b1 << 4 | b2 >> 2;
-      if (j+2 < end) uint8Array[j+2] = b2 << 6 | base64ReverseLookup[b64.charCodeAt(i+3)];
+      uint8Array[j++] = base64ReverseLookup[b64.charCodeAt(i)] << 2 | b1 >> 4;
+      if (j < end) uint8Array[j++] = b1 << 4 | b2 >> 2;
+      if (j < end) uint8Array[j++] = b2 << 6 | base64ReverseLookup[b64.charCodeAt(i+3)];
     }
   })";
   out << expr << '\n';