From 34108547b691f26e11243045f66c72946a5081bf Mon Sep 17 00:00:00 2001
From: Peter Ross <pross@xvid.org>
Date: Tue, 1 Mar 2022 19:50:19 +1100
Subject: [PATCH] AK: Print NaN and infinite numbers in PrintfImplementation

---
 AK/PrintfImplementation.h   | 26 +++++++++++++++++++++++++-
 Tests/LibC/TestSnprintf.cpp | 16 ++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/AK/PrintfImplementation.h b/AK/PrintfImplementation.h
index 1da4294c23..032510503a 100644
--- a/AK/PrintfImplementation.h
+++ b/AK/PrintfImplementation.h
@@ -9,6 +9,7 @@
 #include <AK/Format.h>
 #include <AK/StdLibExtras.h>
 #include <AK/Types.h>
+#include <math.h>
 #include <stdarg.h>
 
 #ifdef __serenity__
@@ -165,7 +166,30 @@ ALWAYS_INLINE int print_double(PutChFunc putch, CharType*& bufptr, double number
 
     u32 whole_width = (field_width >= precision + 1) ? field_width - precision - 1 : 0;
 
-    bool sign = number < 0;
+    bool sign = signbit(number);
+    bool nan = isnan(number);
+    bool inf = isinf(number);
+
+    if (nan || inf) {
+        for (unsigned i = 0; i < field_width - 3 - sign; i++) {
+            putch(bufptr, ' ');
+            length++;
+        }
+        if (sign) {
+            putch(bufptr, '-');
+            length++;
+        }
+        if (nan) {
+            putch(bufptr, 'n');
+            putch(bufptr, 'a');
+            putch(bufptr, 'n');
+        } else {
+            putch(bufptr, 'i');
+            putch(bufptr, 'n');
+            putch(bufptr, 'f');
+        }
+        return length + 3;
+    }
 
     if (sign)
         number = -number;
diff --git a/Tests/LibC/TestSnprintf.cpp b/Tests/LibC/TestSnprintf.cpp
index bfb03d18d7..125f045c6b 100644
--- a/Tests/LibC/TestSnprintf.cpp
+++ b/Tests/LibC/TestSnprintf.cpp
@@ -273,3 +273,19 @@ TEST_CASE(inttypes_macros)
     EXPECT(test_single<uint16_t>({ LITERAL("xxxxxxx"), "|%" PRIx16 "|", 0xC0DE, 6, LITERAL("|c0de|\0") }));
     EXPECT(test_single<uint16_t>({ LITERAL("xxxxxxx"), "|%" PRIX16 "|", 0xC0DE, 6, LITERAL("|C0DE|\0") }));
 }
+
+TEST_CASE(float_values)
+{
+    union {
+        float f;
+        int i;
+    } v;
+
+    v.i = 0x7fc00000;
+    EXPECT(test_single<double>({ LITERAL("xxxxxxx"), "|%4f|", v.f, 6, LITERAL("| nan|\0") }));
+    EXPECT(test_single<double>({ LITERAL("xxxxxxx"), "|%4f|", -v.f, 6, LITERAL("|-nan|\0") }));
+
+    v.i = 0x7f800000;
+    EXPECT(test_single<double>({ LITERAL("xxxxxxx"), "|%4f|", v.f, 6, LITERAL("| inf|\0") }));
+    EXPECT(test_single<double>({ LITERAL("xxxxxxx"), "|%4f|", -v.f, 6, LITERAL("|-inf|\0") }));
+}