From 00b8fba79ed2d14ec8e7fb1e2bcc38f3d59afaef Mon Sep 17 00:00:00 2001
From: Leszek Swirski <[email protected]>
Date: Thu, 20 Feb 2025 14:19:24 +0100
Subject: [PATCH] [conversions] Check for denormal flushing in DoubleToRadixString

Explicitly check the denormal flushing flag in DoubleToRadixString, to
avoid the compiler optimizing away checks against zero.

Bug: 382005099
Fixed: 397731718
Change-Id: If9298e68827bf2e5a1fd987b04b2536bf937a19f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/6286167
Commit-Queue: Leszek Swirski <[email protected]>
Auto-Submit: Leszek Swirski <[email protected]>
Reviewed-by: Jakob Kummerow <[email protected]>
Cr-Commit-Position: refs/heads/main@{#98833}
---

diff --git a/src/numbers/conversions.cc b/src/numbers/conversions.cc
index 95e0036..c8534b7 100644
--- a/src/numbers/conversions.cc
+++ b/src/numbers/conversions.cc
@@ -1251,11 +1251,19 @@
   double fraction = value - integer;
   // We only compute fractional digits up to the input double's precision.
   double delta = 0.5 * (base::Double(value).NextDouble() - value);
-  delta = std::max(base::Double(0.0).NextDouble(), delta);
-  // Delta should always be greater than zero, so long as we're not flushing
-  // denormals to zero.
-  DCHECK_IMPLIES(!(delta > 0.0), base::FPU::GetFlushDenormals());
-  if (delta > 0.0 && fraction >= delta) {
+  bool delta_is_positive = true;
+  // If the delta rounded down to zero, use the minimum (denormal) delta
+  // value. Be careful around denormal flushing when doing so.
+  if (delta <= 0) {
+    if (base::FPU::GetFlushDenormals()) {
+      // We're flushing the delta value to zero, so the loop below won't
+      // make progress. Skip it instead.
+      delta_is_positive = false;
+    } else {
+      delta = base::Double(0.0).NextDouble();
+    }
+  }
+  if (delta_is_positive && fraction >= delta) {
     // Insert decimal point.
     buffer[fraction_cursor++] = '.';
     do {