Revert "Revert "Cleanup some numeric code.""

core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp

Index: core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
diff --git a/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp b/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
index 3057948959807b1e84e336729ad5ee6dc3efe3c2..dd31322744e15d7d2c01492af2ca95826e300ce3 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_parser.cpp
@@ -7,6 +7,7 @@
 #include "../../../include/fpdfapi/fpdf_page.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../../../include/fpdfapi/fpdf_serial.h"
+#include "../../../include/fxcrt/fx_ext.h"
 #include "pageint.h"
 
 #define REQUIRE_PARAMS(count)  \
@@ -1534,40 +1535,26 @@ void CPDF_StreamContentParser::AddPathObject(int FillType, FX_BOOL bStroke) {
 }
 CFX_ByteString _FPDF_ByteStringFromHex(CFX_BinaryBuf& src_buf) {
   CFX_ByteTextBuf buf;
-  FX_BOOL bFirst = TRUE;
+  bool bFirst = true;
   int code = 0;
   const uint8_t* str = src_buf.GetBuffer();
   FX_DWORD size = src_buf.GetSize();
   for (FX_DWORD i = 0; i < size; i++) {
     uint8_t ch = str[i];
-    if (ch >= '0' && ch <= '9') {
-      if (bFirst) {
-        code = (ch - '0') * 16;
-      } else {
-        code += ch - '0';
-        buf.AppendChar((char)code);
-      }
-      bFirst = !bFirst;
-    } else if (ch >= 'A' && ch <= 'F') {
-      if (bFirst) {
-        code = (ch - 'A' + 10) * 16;
-      } else {
-        code += ch - 'A' + 10;
-        buf.AppendChar((char)code);
-      }
-      bFirst = !bFirst;
-    } else if (ch >= 'a' && ch <= 'f') {
+
+    if (std::isxdigit(ch)) {
+      int val = FXSYS_toHexDigit(ch);
       if (bFirst) {
-        code = (ch - 'a' + 10) * 16;
+        code = val * 16;
       } else {
-        code += ch - 'a' + 10;
+        code += val;
         buf.AppendChar((char)code);
       }
       bFirst = !bFirst;
     }
   }
-  if (!bFirst) {
+  if (!bFirst)
     buf.AppendChar((char)code);
-  }
+
   return buf.GetByteString();
 }