[vm] Revise Dart_IntegerToHexCString to avoid dependency on Bigint

runtime/vm/object.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/become.h"
@@ skipping 18220 matching lines @@
     if (Smi::IsValid(value)) {
       // This cast is safe because Smi::IsValid verifies that value will fit.
       intptr_t val = static_cast<intptr_t>(value);
       return Smi::New(val);
     }
     return Mint::New(value);
   }
   return raw();
 }
 
+const char* Integer::ToHexCString(Zone* zone) const {
+  ASSERT(IsSmi() || IsMint());  // Bigint has its own implementation.
+  int64_t value = AsInt64Value();
+  if (value < 0) {
+    return OS::SCreate(zone, "-0x%" PRIX64, static_cast<uint64_t>(-value));

[zra, 2017/08/01 16:21:57]

We have some abbreviations for these here:

https://github.com/dart-lang/sdk/blob/master/runtime/platform/globals.h#L390

Also, I think they have to be followed by "", so:

OS::SCreate(zone, "-0x%" Px64 "", ...)

[alexmarkov, 2017/08/01 17:40:11]

Introduced new short form specifier PX64, see
https://codereview.chromium.org/2985423002/
I think there is no need in trailing "", because these format specifier
constants are just string literals like "d" or "llx". Can you clarify why
appending an empty string at the end is useful?

+  } else {
+    return OS::SCreate(zone, "0x%" PRIX64, static_cast<uint64_t>(value));
+  }
+}
+
 RawInteger* Integer::ArithmeticOp(Token::Kind operation,
                                   const Integer& other,
                                   Heap::Space space) const {
   // In 32-bit mode, the result of any operation between two Smis will fit in a
   // 32-bit signed result, except the product of two Smis, which will be 64-bit.
   // In 64-bit mode, the result of any operation between two Smis will fit in a
   // 64-bit signed result, except the product of two Smis (see below).
   if (IsSmi() && other.IsSmi()) {
     const intptr_t left_value = Smi::Value(Smi::RawCast(raw()));
     const intptr_t right_value = Smi::Value(Smi::RawCast(other.raw()));
@@ skipping 4282 matching lines @@
   }
   return UserTag::null();
 }
 
 const char* UserTag::ToCString() const {
   const String& tag_label = String::Handle(label());
   return tag_label.ToCString();
 }
 
 }  // namespace dart