Revert "Revert "Cleanup some numeric code.""

core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp

Index: core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp
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 1fa27e38051b97ee4ee09225615041f9921dca56..88e2269c7ad81e724fcd723a32e0ccc7d3132c16 100644
--- a/core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp
+++ b/core/src/fpdfapi/fpdf_page/fpdf_page_parser_old.cpp
@@ -7,6 +7,7 @@
 #include "../../../include/fpdfapi/fpdf_page.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../../../include/fxcodec/fx_codec.h"
+#include "../../../include/fxcrt/fx_ext.h"
 #include "pageint.h"
 #include <limits.h>
 
@@ -875,34 +876,20 @@ CFX_ByteString CPDF_StreamParser::ReadHexString() {
   FX_BOOL bFirst = TRUE;
   int code = 0;
   while (1) {
-    if (ch == '>') {
+    if (ch == '>')
       break;
-    }
-    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 = HexCharToDigit(ch);
       if (bFirst) {
-        code = (ch - 'a' + 10) * 16;
+        code = val * 16;
       } else {
-        code += ch - 'a' + 10;
-        buf.AppendChar((char)code);
+        code += val;
+        buf.AppendByte((uint8_t)code);
       }
       bFirst = !bFirst;
     }
+
     if (!PositionIsInBounds())
       break;