From 1472f6d9865eec67230405522bc0b44a681440dc Mon Sep 17 00:00:00 2001
From: Daniel Bertalan <dani@danielbertalan.dev>
Date: Fri, 6 Aug 2021 21:47:49 +0200
Subject: [PATCH] AK: Add formatting for infinity and NaN

Without this patch, we would end up printing garbage values when we
encountered floating point infinity or NaN values, and also triggered
UBSAN with Clang. This added code models `std::format`'s behavior: the
sign is added the same way as with normal values and the strings 'nan'
and 'inf' are printed.
---
 AK/Format.cpp | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)

diff --git a/AK/Format.cpp b/AK/Format.cpp
index 08653293c8..a7dc73f4ff 100644
--- a/AK/Format.cpp
+++ b/AK/Format.cpp
@@ -19,6 +19,7 @@
 #    include <Kernel/Process.h>
 #    include <Kernel/Thread.h>
 #else
+#    include <math.h>
 #    include <stdio.h>
 #    include <string.h>
 #endif
@@ -344,6 +345,22 @@ void FormatBuilder::put_f64(
     StringBuilder string_builder;
     FormatBuilder format_builder { string_builder };
 
+    if (isnan(value) || isinf(value)) [[unlikely]] {
+        if (value < 0.0)
+            string_builder.append('-');
+        else if (sign_mode == SignMode::Always)
+            string_builder.append('+');
+        else
+            string_builder.append(' ');
+
+        if (isnan(value))
+            string_builder.append(upper_case ? "NAN"sv : "nan"sv);
+        else
+            string_builder.append(upper_case ? "INF"sv : "inf"sv);
+        format_builder.put_string(string_builder.string_view(), align, min_width, NumericLimits<size_t>::max(), fill);
+        return;
+    }
+
     bool is_negative = value < 0.0;
     if (is_negative)
         value = -value;
@@ -394,6 +411,22 @@ void FormatBuilder::put_f80(
     StringBuilder string_builder;
     FormatBuilder format_builder { string_builder };
 
+    if (isnan(value) || isinf(value)) [[unlikely]] {
+        if (value < 0.0l)
+            string_builder.append('-');
+        else if (sign_mode == SignMode::Always)
+            string_builder.append('+');
+        else
+            string_builder.append(' ');
+
+        if (isnan(value))
+            string_builder.append(upper_case ? "NAN"sv : "nan"sv);
+        else
+            string_builder.append(upper_case ? "INF"sv : "inf"sv);
+        format_builder.put_string(string_builder.string_view(), align, min_width, NumericLimits<size_t>::max(), fill);
+        return;
+    }
+
     bool is_negative = value < 0.0l;
     if (is_negative)
         value = -value;