Revert "Revert "Cleanup some numeric code.""

core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp

Index: core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
diff --git a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
index 255d0ce29cade6840340e5ac51253341f1a0985e..eaff29d8125680515dd0401880a003bf0350554a 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
@@ -8,6 +8,7 @@
 #include "../../../include/fpdfapi/fpdf_parser.h"
 #include "../../../include/fpdfapi/fpdf_module.h"
 #include "../../../include/fxcodec/fx_codec.h"
+#include "../../../include/fxcrt/fx_ext.h"
 
 #define _STREAM_MAX_SIZE_ 20 * 1024 * 1024
 
@@ -135,23 +136,20 @@ FX_DWORD _HexDecode(const uint8_t* src_buf,
       continue;
 
     int digit;
-    if (ch <= '9' && ch >= '0') {
-      digit = ch - '0';
-    } else if (ch <= 'f' && ch >= 'a') {
-      digit = ch - 'a' + 10;
-    } else if (ch <= 'F' && ch >= 'A') {
-      digit = ch - 'A' + 10;
+    if (std::isxdigit(ch)) {
+      digit = HexCharToDigit(ch);
     } else if (ch == '>') {
       i++;
       break;
     } else {
       continue;
     }
-    if (bFirstDigit) {
+
+    if (bFirstDigit)
       dest_buf[dest_size] = digit * 16;
-    } else {
+    else
       dest_buf[dest_size++] += digit;
-    }
+
     bFirstDigit = !bFirstDigit;
   }
   if (!bFirstDigit) {