Revert "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 3ea554b2d869ceacdaf75fd73262d6104fb8b9d5..e68fcb6800a30792db44dc2ec3f56e96c260a882 100644
--- a/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
+++ b/core/src/fpdfapi/fpdf_parser/fpdf_parser_decode.cpp
@@ -8,7 +8,6 @@
 #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
 
@@ -129,32 +128,37 @@ FX_DWORD HexDecode(const uint8_t* src_buf,
     }
   dest_buf = FX_Alloc(uint8_t, i / 2 + 1);
   dest_size = 0;
-  bool bFirst = true;
+  FX_BOOL bFirstDigit = TRUE;
   for (i = 0; i < src_size; i++) {
     uint8_t ch = src_buf[i];
     if (PDFCharIsLineEnding(ch) || ch == ' ' || ch == '\t')
       continue;
 
-    if (ch == '>') {
-      ++i;
+    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;
+    } else if (ch == '>') {
+      i++;
       break;
-    }
-    if (!std::isxdigit(ch))
+    } else {
       continue;
-
-    int digit = FXSYS_toHexDigit(ch);
-    if (bFirst)
+    }
+    if (bFirstDigit) {
       dest_buf[dest_size] = digit * 16;
-    else
+    } else {
       dest_buf[dest_size++] += digit;
-
-    bFirst = !bFirst;
+    }
+    bFirstDigit = !bFirstDigit;
   }
-  if (!bFirst)
+  if (!bFirstDigit) {
     dest_size++;
+  }
   return i;
 }
-
 FX_DWORD RunLengthDecode(const uint8_t* src_buf,
                          FX_DWORD src_size,
                          uint8_t*& dest_buf,