Fix MSVC warnings about possible value truncation.

src/hdmx.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "hdmx.h"
 #include "head.h"
 #include "maxp.h"
 
 // hdmx - Horizontal Device Metrics
 // http://www.microsoft.com/opentype/otspec/hdmx.htm
@@ skipping 87 matching lines @@
 
 bool ots_hdmx_should_serialise(OpenTypeFile *file) {
   if (!file->hdmx) return false;
   if (!file->glyf) return false;  // this table is not for CFF fonts.
   return true;
 }
 
 bool ots_hdmx_serialise(OTSStream *out, OpenTypeFile *file) {
   OpenTypeHDMX * const hdmx = file->hdmx;
 
-  if (!out->WriteU16(hdmx->version) ||
-      !out->WriteS16(hdmx->records.size()) ||
+  const int16_t num_recs = static_cast<int16_t>(hdmx->records.size());
+  if (hdmx->records.size() >
+          static_cast<size_t>(std::numeric_limits<int16_t>::max()) ||
+      !out->WriteU16(hdmx->version) ||
+      !out->WriteS16(num_recs) ||
       !out->WriteS32(hdmx->size_device_record)) {
     return OTS_FAILURE();
   }
 
-  for (unsigned i = 0; i < hdmx->records.size(); ++i) {
+  for (int16_t i = 0; i < num_recs; ++i) {
     const OpenTypeHDMXDeviceRecord& rec = hdmx->records[i];
     if (!out->Write(&rec.pixel_size, 1) ||
         !out->Write(&rec.max_width, 1) ||
         !out->Write(&rec.widths[0], rec.widths.size())) {
       return OTS_FAILURE();
     }
     if ((hdmx->pad_len > 0) &&
         !out->Write((const uint8_t *)"\x00\x00\x00", hdmx->pad_len)) {
       return OTS_FAILURE();
     }
   }
 
   return true;
 }
 
 void ots_hdmx_free(OpenTypeFile *file) {
   delete file->hdmx;
 }
 
 }  // namespace ots