Revert "Revert "Cleanup some numeric code.""

core/src/fxcrt/fx_extension.cpp

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include "../../include/fxcrt/fx_basic.h"
 #include "../../include/fxcrt/fx_ext.h"
 #include "extension.h"
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
 #include <wincrypt.h>
 #else
 #include <ctime>
 #endif
 
+#include <cctype>
+
+int HexCharToDigit(char c) {
+  if (!std::isxdigit(c))
+    return 0;
+  char upchar = std::toupper(c);
+  return upchar > '9' ? upchar - 'A' + 10 : upchar - '0';
+}
+
 IFX_FileStream* FX_CreateFileStream(const FX_CHAR* filename, FX_DWORD dwModes) {
   IFXCRT_FileAccess* pFA = FXCRT_FileAccess_Create();
   if (!pFA) {
     return NULL;
   }
   if (!pFA->Open(filename, dwModes)) {
     pFA->Release();
     return NULL;
   }
   return new CFX_CRTFileStream(pFA);
@@ skipping 267 matching lines @@
 void FX_Random_GenerateCrypto(FX_DWORD* pBuffer, int32_t iCount) {
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
   FX_GenerateCryptoRandom(pBuffer, iCount);
 #else
   FX_Random_GenerateBase(pBuffer, iCount);
 #endif
 }
 #ifdef __cplusplus
 }
 #endif