fixup! lib: refactor internal webidl converters

Signed-off-by: Filip Skokan <panva.ip@gmail.com>

Author: panva

lib/internal/webidl.js

@@ -328,6 +328,18 @@ function convertToInt(
     upperBound = pow2(bitLength - 1) - 1;
   }
 
+  // Common case: primitive Number values that already fit the Web IDL
+  // range and have no fractional part are returned unchanged by every
+  // ConvertToInt path, except that -0 must become +0. This skips the
+  // generic ToNumber and option handling without skipping observable
+  // object coercion.
+  if (typeof V === 'number' &&
+      V >= lowerBound &&
+      V <= upperBound &&
+      MathTrunc(V) === V) {
+    return V === 0 ? 0 : V;
+  }
+
   // Step 4: convert V with ECMA-262 ToNumber.
   let x = toNumber(V, options);
   // Step 5: normalize -0 to +0.
@@ -373,6 +385,14 @@ function convertToInt(
   // Step 9: truncate to IntegerPart(x).
   x = integerPart(x);
 
+  // Steps 10-12 are an identity for values already in the step 1-3
+  // bounds. For 64-bit conversions this only skips the safe-integer
+  // subset; values outside it still need exact BigInt modulo and the
+  // final Number approximation.
+  if (x >= lowerBound && x <= upperBound) {
+    return x;
+  }
+
   if (bitLength === 64) {
     // Steps 10-12 still wrap over the full 2^64 IDL integer range.
     // BigInt keeps x modulo 2^64 and the signed high-bit adjustment exact
@@ -396,11 +416,13 @@ function convertToInt(
   }
 
   // Step 10: reduce modulo 2^bitLength.
-  x = modulo(x, pow2(bitLength));
+  const twoToTheBitLength = pow2(bitLength);
+  const twoToOneLessThanTheBitLength = pow2(bitLength - 1);
+  x = modulo(x, twoToTheBitLength);
 
   // Step 11: wrap into the signed range when the high bit is set.
-  if (signed && x >= pow2(bitLength - 1)) {
-    return x - pow2(bitLength);
+  if (signed && x >= twoToOneLessThanTheBitLength) {
+    return x - twoToTheBitLength;
   }
 
   // Step 12: return the unsigned value.