diff --git a/core/include/fxcrt/fx_ext.h b/core/include/fxcrt/fx_ext.h
index 3f4f668..c8afb2b 100644
--- a/core/include/fxcrt/fx_ext.h
+++ b/core/include/fxcrt/fx_ext.h
@@ -53,13 +53,21 @@
   return upchar > '9' ? upchar - 'A' + 10 : upchar - '0';
 }
 
+inline bool FXSYS_isDecimalDigit(const FX_CHAR c) {
+  return std::isdigit(c);
+}
+
+inline bool FXSYS_isDecimalDigit(const FX_WCHAR c) {
+  return std::iswdigit(c);
+}
+
 inline int FXSYS_toDecimalDigit(const FX_CHAR c) {
   if (!std::isdigit(c))
     return 0;
   return c - '0';
 }
 
-inline int FXSYS_toDecimalDigitWide(const FX_WCHAR c) {
+inline int FXSYS_toDecimalDigit(const FX_WCHAR c) {
   if (!std::iswdigit(c))
     return 0;
   return c - L'0';
diff --git a/core/src/fpdfapi/fpdf_font/fpdf_font_cid.cpp b/core/src/fpdfapi/fpdf_font/fpdf_font_cid.cpp
index 3cbd676..7c85b82 100644
--- a/core/src/fpdfapi/fpdf_font/fpdf_font_cid.cpp
+++ b/core/src/fpdfapi/fpdf_font/fpdf_font_cid.cpp
@@ -720,7 +720,7 @@
   }
 
   for (int i = 0; i < word.GetLength() && std::isdigit(word.GetAt(i)); ++i)
-    num = num * 10 + FXSYS_toDecimalDigit(word.GetAt(i));
+    num = num * 10 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(word.GetAt(i)));
   return num;
 }
 
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp
index 02e3617..b49607e 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp
@@ -533,10 +533,11 @@
   if (!PositionIsInBounds())
     return CFX_ByteString();
 
-  int ch = m_pBuf[m_Pos++];
+  uint8_t ch = m_pBuf[m_Pos++];
   CFX_ByteTextBuf buf;
   int parlevel = 0;
-  int status = 0, iEscCode = 0;
+  int status = 0;
+  int iEscCode = 0;
   while (1) {
     switch (status) {
       case 0:
@@ -560,7 +561,7 @@
         break;
       case 1:
         if (ch >= '0' && ch <= '7') {
-          iEscCode = FXSYS_toDecimalDigit(ch);
+          iEscCode = FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           status = 2;
           break;
         }
@@ -585,7 +586,8 @@
         break;
       case 2:
         if (ch >= '0' && ch <= '7') {
-          iEscCode = iEscCode * 8 + FXSYS_toDecimalDigit(ch);
+          iEscCode =
+              iEscCode * 8 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           status = 3;
         } else {
           buf.AppendChar(iEscCode);
@@ -595,7 +597,8 @@
         break;
       case 3:
         if (ch >= '0' && ch <= '7') {
-          iEscCode = iEscCode * 8 + FXSYS_toDecimalDigit(ch);
+          iEscCode =
+              iEscCode * 8 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           buf.AppendChar(iEscCode);
           status = 0;
         } else {
@@ -617,7 +620,7 @@
     ch = m_pBuf[m_Pos++];
   }
   if (PositionIsInBounds())
-    ch = m_pBuf[m_Pos++];
+    ++m_Pos;
 
   if (buf.GetLength() > MAX_STRING_LENGTH) {
     return CFX_ByteString(buf.GetBuffer(), MAX_STRING_LENGTH);
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
index 16d1134..737bbe4 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_parser.cpp
@@ -208,12 +208,12 @@
   if (!m_Syntax.GetCharAt(5, ch))
     return FORMAT_ERROR;
   if (std::isdigit(ch))
-    m_FileVersion = FXSYS_toDecimalDigit(ch) * 10;
+    m_FileVersion = FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch)) * 10;
 
   if (!m_Syntax.GetCharAt(7, ch))
     return FORMAT_ERROR;
   if (std::isdigit(ch))
-    m_FileVersion += FXSYS_toDecimalDigit(ch);
+    m_FileVersion += FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
 
   if (m_Syntax.m_FileLen < m_Syntax.m_HeaderOffset + 9)
     return FORMAT_ERROR;
@@ -669,7 +669,7 @@
           if (std::isdigit(byte)) {
             start_pos = pos + i;
             state = ParserState::kObjNum;
-            objnum = FXSYS_toDecimalDigit(byte);
+            objnum = FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(byte));
           } else if (byte == 't') {
             state = ParserState::kTrailer;
             inside_index = 1;
@@ -684,7 +684,8 @@
 
         case ParserState::kObjNum:
           if (std::isdigit(byte)) {
-            objnum = objnum * 10 + FXSYS_toDecimalDigit(byte);
+            objnum =
+                objnum * 10 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(byte));
           } else if (PDFCharIsWhitespace(byte)) {
             state = ParserState::kPostObjNum;
           } else {
@@ -698,7 +699,7 @@
           if (std::isdigit(byte)) {
             start_pos1 = pos + i;
             state = ParserState::kGenNum;
-            gennum = FXSYS_toDecimalDigit(byte);
+            gennum = FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(byte));
           } else if (byte == 't') {
             state = ParserState::kTrailer;
             inside_index = 1;
@@ -710,7 +711,8 @@
 
         case ParserState::kGenNum:
           if (std::isdigit(byte)) {
-            gennum = gennum * 10 + FXSYS_toDecimalDigit(byte);
+            gennum =
+                gennum * 10 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(byte));
           } else if (PDFCharIsWhitespace(byte)) {
             state = ParserState::kPostGenNum;
           } else {
@@ -725,7 +727,7 @@
             inside_index = 1;
           } else if (std::isdigit(byte)) {
             objnum = gennum;
-            gennum = FXSYS_toDecimalDigit(byte);
+            gennum = FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(byte));
             start_pos = start_pos1;
             start_pos1 = pos + i;
             state = ParserState::kGenNum;
@@ -1876,7 +1878,7 @@
         break;
       case 1:
         if (ch >= '0' && ch <= '7') {
-          iEscCode = FXSYS_toDecimalDigit(ch);
+          iEscCode = FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           status = 2;
           break;
         }
@@ -1901,7 +1903,8 @@
         break;
       case 2:
         if (ch >= '0' && ch <= '7') {
-          iEscCode = iEscCode * 8 + FXSYS_toDecimalDigit(ch);
+          iEscCode =
+              iEscCode * 8 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           status = 3;
         } else {
           buf.AppendChar(iEscCode);
@@ -1911,7 +1914,8 @@
         break;
       case 3:
         if (ch >= '0' && ch <= '7') {
-          iEscCode = iEscCode * 8 + FXSYS_toDecimalDigit(ch);
+          iEscCode =
+              iEscCode * 8 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           buf.AppendChar(iEscCode);
           status = 0;
         } else {
diff --git a/core/src/fxcrt/fx_basic_gcc.cpp b/core/src/fxcrt/fx_basic_gcc.cpp
index 607f095..e2ec939 100644
--- a/core/src/fxcrt/fx_basic_gcc.cpp
+++ b/core/src/fxcrt/fx_basic_gcc.cpp
@@ -11,42 +11,19 @@
 #include "core/include/fxcrt/fx_ext.h"
 #include "core/include/fxcrt/fx_string.h"
 
-template <class T>
-T FXSYS_StrToInt(const FX_CHAR* str) {
-  bool neg = false;
+template <typename IntType, typename CharType>
+IntType FXSYS_StrToInt(const CharType* str) {
   if (!str)
     return 0;
 
-  if (std::numeric_limits<T>::is_signed && *str == '-') {
-    neg = true;
+  bool neg = std::numeric_limits<IntType>::is_signed && *str == '-';
+  if (neg)
     str++;
-  }
-  T num = 0;
-  while (*str && std::isdigit(*str)) {
-    T val = FXSYS_toDecimalDigit(*str);
-    if (num > (std::numeric_limits<T>::max() - val) / 10)
-      break;
 
-    num = num * 10 + val;
-    str++;
-  }
-  return neg ? -num : num;
-}
-
-template <class T>
-T FXSYS_StrToInt(const FX_WCHAR* str) {
-  bool neg = false;
-  if (!str)
-    return 0;
-
-  if (std::numeric_limits<T>::is_signed && *str == '-') {
-    neg = true;
-    str++;
-  }
-  T num = 0;
-  while (*str && std::iswdigit(*str)) {
-    T val = FXSYS_toDecimalDigitWide(*str);
-    if (num > (std::numeric_limits<T>::max() - val) / 10)
+  IntType num = 0;
+  while (*str && FXSYS_isDecimalDigit(*str)) {
+    IntType val = FXSYS_toDecimalDigit(*str);
+    if (num > (std::numeric_limits<IntType>::max() - val) / 10)
       break;
 
     num = num * 10 + val;
@@ -93,19 +70,19 @@
 extern "C" {
 #endif
 int32_t FXSYS_atoi(const FX_CHAR* str) {
-  return FXSYS_StrToInt<int32_t>(str);
+  return FXSYS_StrToInt<int32_t, FX_CHAR>(str);
 }
 uint32_t FXSYS_atoui(const FX_CHAR* str) {
   return FXSYS_StrToInt<uint32_t>(str);
 }
 int32_t FXSYS_wtoi(const FX_WCHAR* str) {
-  return FXSYS_StrToInt<int32_t>(str);
+  return FXSYS_StrToInt<int32_t, FX_WCHAR>(str);
 }
 int64_t FXSYS_atoi64(const FX_CHAR* str) {
-  return FXSYS_StrToInt<int64_t>(str);
+  return FXSYS_StrToInt<int64_t, FX_CHAR>(str);
 }
 int64_t FXSYS_wtoi64(const FX_WCHAR* str) {
-  return FXSYS_StrToInt<int64_t>(str);
+  return FXSYS_StrToInt<int64_t, FX_WCHAR>(str);
 }
 const FX_CHAR* FXSYS_i64toa(int64_t value, FX_CHAR* str, int radix) {
   return FXSYS_IntToStr<int64_t, uint64_t, FX_CHAR*>(value, str, radix);
diff --git a/core/src/fxcrt/fx_basic_wstring.cpp b/core/src/fxcrt/fx_basic_wstring.cpp
index 396dbc4..8df7246 100644
--- a/core/src/fxcrt/fx_basic_wstring.cpp
+++ b/core/src/fxcrt/fx_basic_wstring.cpp
@@ -994,7 +994,7 @@
     if (str[cc] == '.') {
       break;
     }
-    integer = integer * 10 + FXSYS_toDecimalDigitWide(str[cc]);
+    integer = integer * 10 + FXSYS_toDecimalDigit(str[cc]);
     cc++;
   }
   FX_FLOAT fraction = 0;
@@ -1002,7 +1002,7 @@
     cc++;
     FX_FLOAT scale = 0.1f;
     while (cc < len) {
-      fraction += scale * FXSYS_toDecimalDigitWide(str[cc]);
+      fraction += scale * FXSYS_toDecimalDigit(str[cc]);
       scale *= 0.1f;
       cc++;
     }
diff --git a/core/src/fxcrt/fx_extension_unittest.cpp b/core/src/fxcrt/fx_extension_unittest.cpp
index b12dcbe..e2ae870 100644
--- a/core/src/fxcrt/fx_extension_unittest.cpp
+++ b/core/src/fxcrt/fx_extension_unittest.cpp
@@ -16,9 +16,13 @@
 TEST(fxcrt, FXSYS_toDecimalDigit) {
   EXPECT_EQ(7, FXSYS_toDecimalDigit('7'));
   EXPECT_EQ(0, FXSYS_toDecimalDigit('a'));
+  EXPECT_EQ(7, FXSYS_toDecimalDigit(L'7'));
+  EXPECT_EQ(0, FXSYS_toDecimalDigit(L'a'));
 }
 
-TEST(fxcrt, FXSYS_toDecimalDigitWide) {
-  EXPECT_EQ(7, FXSYS_toDecimalDigitWide(L'7'));
-  EXPECT_EQ(0, FXSYS_toDecimalDigitWide(L'a'));
+TEST(fxcrt, FXSYS_isDecimalDigit) {
+  EXPECT_TRUE(FXSYS_isDecimalDigit('7'));
+  EXPECT_TRUE(FXSYS_isDecimalDigit(L'7'));
+  EXPECT_FALSE(FXSYS_isDecimalDigit('a'));
+  EXPECT_FALSE(FXSYS_isDecimalDigit(L'a'));
 }
diff --git a/core/src/fxcrt/fx_xml_parser.cpp b/core/src/fxcrt/fx_xml_parser.cpp
index ab729ee..59c3de4 100644
--- a/core/src/fxcrt/fx_xml_parser.cpp
+++ b/core/src/fxcrt/fx_xml_parser.cpp
@@ -231,7 +231,7 @@
             break;
           }
           if (g_FXCRT_XML_IsDigital(ch))
-            code = code * 10 + FXSYS_toDecimalDigit(ch);
+            code = code * 10 + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
           break;
         case 4:
           m_dwIndex++;
@@ -243,7 +243,8 @@
               g_FXCRT_XML_ByteTypes[ch] & FXCRTM_XML_CHARTYPE_HexChar;
           if (nHex) {
             if (nHex == FXCRTM_XML_CHARTYPE_HexDigital) {
-              code = (code << 4) + FXSYS_toDecimalDigit(ch);
+              code =
+                  (code << 4) + FXSYS_toDecimalDigit(static_cast<FX_WCHAR>(ch));
             } else if (nHex == FXCRTM_XML_CHARTYPE_HexLowerLetter) {
               code = (code << 4) + ch - 87;
             } else {
diff --git a/fpdfsdk/src/javascript/PublicMethods.cpp b/fpdfsdk/src/javascript/PublicMethods.cpp
index f510d51..f228072 100644
--- a/fpdfsdk/src/javascript/PublicMethods.cpp
+++ b/fpdfsdk/src/javascript/PublicMethods.cpp
@@ -242,7 +242,7 @@
     if (!FXSYS_iswdigit(c))
       break;
 
-    nRet = nRet * 10 + FXSYS_toDecimalDigitWide(c);
+    nRet = nRet * 10 + FXSYS_toDecimalDigit(c);
     nSkip = i - nStart + 1;
     if (nSkip >= nMaxStep)
       break;
diff --git a/fpdfsdk/src/javascript/util.cpp b/fpdfsdk/src/javascript/util.cpp
index 4bc28cd..c9149be 100644
--- a/fpdfsdk/src/javascript/util.cpp
+++ b/fpdfsdk/src/javascript/util.cpp
@@ -512,30 +512,6 @@
   return TRUE;
 }
 
-int64_t FX_atoi64(const char* nptr) {
-  int c;         /* current char */
-  int64_t total; /* current total */
-  int sign;      /* if '-', then negative, otherwise positive */
-
-  /* skip whitespace */
-  while (isspace((int)(unsigned char)*nptr))
-    ++nptr;
-
-  c = (int)(unsigned char)*nptr++;
-  sign = c; /* save sign indication */
-  if (c == '-' || c == '+')
-    c = (int)(unsigned char)*nptr++; /* skip sign */
-
-  total = 0;
-
-  while (isdigit(c)) {
-    total = 10 * total + FXSYS_toDecimalDigit(c); /* accumulate digit */
-    c = (int)(unsigned char)*nptr++; /* get next char */
-  }
-
-  return sign == '-' ? -total : total;
-}
-
 FX_BOOL util::byteToChar(IJS_Context* cc,
                          const std::vector<CJS_Value>& params,
                          CJS_Value& vRet,
diff --git a/fpdfsdk/src/javascript/util.h b/fpdfsdk/src/javascript/util.h
index 22a8358..9441b11 100644
--- a/fpdfsdk/src/javascript/util.h
+++ b/fpdfsdk/src/javascript/util.h
@@ -63,6 +63,4 @@
   JS_STATIC_METHOD(byteToChar, util);
 };
 
-int64_t FX_atoi64(const char* nptr);
-
 #endif  // FPDFSDK_SRC_JAVASCRIPT_UTIL_H_