Bug 1350097 - handle very long floating point output in cvt_f; r=froydnj

Bug 1350097 points out a case where the assertion in cvt_f, added in
https://bugzilla.mozilla.org/show_bug.cgi?id=1060419#c127, triggers.
Before this addition, code calling this printf variant would end up just
printing something invalid, as the truncated value would be emitted.
This patch increases the buffer size to be sufficient for DBL_MAX.

MozReview-Commit-ID: AVphURGa6jL

--HG--
extra : rebase_source : c7a2dad8e496434a631441ccc25dfee2db1ea71a

js/src/jsapi-tests/testPrintf.cpp

@@ -8,6 +8,7 @@
 #include "mozilla/IntegerPrintfMacros.h"
 #include "mozilla/SizePrintfMacros.h"
 
+#include <cfloat>
 #include <stdarg.h>
 
 #include "jsprf.h"
@@ -61,6 +62,10 @@ BEGIN_TEST(testPrintf)
     CHECK(print_one("1.500000", "%f", 1.5f));
     CHECK(print_one("1.5", "%g", 1.5));
 
+    // Regression test for bug#1350097.  The bug was an assertion
+    // failure caused by printing a very long floating point value.
+    print_one("ignore", "%lf", DBL_MAX);
+
     CHECK(print_one("2727", "%" PRIu32, (uint32_t) 2727));
     CHECK(print_one("aa7", "%" PRIx32, (uint32_t) 2727));
     CHECK(print_one("2727", "%" PRIu64, (uint64_t) 2727));

mozglue/misc/Printf.cpp

@@ -255,7 +255,8 @@ bool
 mozilla::PrintfTarget::cvt_f(double d, const char* fmt0, const char* fmt1)
 {
     char fin[20];
-    char fout[300];
+    // The size is chosen such that we can print DBL_MAX.  See bug#1350097.
+    char fout[320];
     int amount = fmt1 - fmt0;
 
     MOZ_ASSERT((amount > 0) && (amount < (int)sizeof(fin)));
@@ -277,7 +278,7 @@ mozilla::PrintfTarget::cvt_f(double d, const char* fmt0, const char* fmt1)
     }
 #endif
     size_t len = SprintfLiteral(fout, fin, d);
-    MOZ_ASSERT(len <= sizeof(fout));
+    MOZ_RELEASE_ASSERT(len <= sizeof(fout));
 
     return emit(fout, len);
 }