From 33bfe42017dba7a14e993860bff4d6ea7990391e Mon Sep 17 00:00:00 2001
From: Uwe Seimet <48174652+uweseimet@users.noreply.github.com>
Date: Sun, 27 Feb 2022 22:24:50 +0100
Subject: [PATCH] Replaced zlib by internal crc32() method (#698)

---
 src/raspberrypi/Makefile               |  2 +-
 src/raspberrypi/devices/ctapdriver.cpp | 23 +++++++++++++++--------
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/raspberrypi/Makefile b/src/raspberrypi/Makefile
index e3c47d87..a623b12a 100644
--- a/src/raspberrypi/Makefile
+++ b/src/raspberrypi/Makefile
@@ -183,7 +183,7 @@ ALL: all
 docs: $(DOC_DIR)/rascsi_man_page.txt $(DOC_DIR)/rasctl_man_page.txt $(DOC_DIR)/scsimon_man_page.txt
 
 $(BINDIR)/$(RASCSI): $(SRC_PROTOBUF) $(OBJ_RASCSI) | $(BINDIR)
-	$(CXX) $(CXXFLAGS) -o $@ $(OBJ_RASCSI) -lpthread -lz -lpcap -lprotobuf -lstdc++fs
+	$(CXX) $(CXXFLAGS) -o $@ $(OBJ_RASCSI) -lpthread -lpcap -lprotobuf -lstdc++fs
 
 $(BINDIR)/$(RASCTL): $(SRC_PROTOBUF) $(OBJ_RASCTL) | $(BINDIR)
 	$(CXX) $(CXXFLAGS) -o $@ $(OBJ_RASCTL) -lpthread -lprotobuf -lstdc++fs
diff --git a/src/raspberrypi/devices/ctapdriver.cpp b/src/raspberrypi/devices/ctapdriver.cpp
index 01a540e7..3a328339 100644
--- a/src/raspberrypi/devices/ctapdriver.cpp
+++ b/src/raspberrypi/devices/ctapdriver.cpp
@@ -18,8 +18,6 @@
 #include <sys/ioctl.h>
 #include <linux/sockios.h>
 #endif
-// TODO Try to get rid of zlib, there is only one operation using it
-#include <zlib.h> // For crc32()
 #include "os.h"
 #include "ctapdriver.h"
 #include "log.h"
@@ -447,6 +445,19 @@ bool CTapDriver::PendingPackets()
 	}
 }
 
+// See https://stackoverflow.com/questions/21001659/crc32-algorithm-implementation-in-c-without-a-look-up-table-and-with-a-public-li
+uint32_t crc32(BYTE *buf, int length) {
+   uint32_t crc = 0xffffffff;
+   for (int i = 0; i < length; i++) {
+      crc ^= buf[i];
+      for (int j = 0; j < 8; j++) {
+         uint32_t mask = -(crc & 1);
+         crc = (crc >> 1) ^ (0xEDB88320 & mask);
+      }
+   }
+   return ~crc;
+}
+
 //---------------------------------------------------------------------------
 //
 //	Receive
@@ -457,7 +468,7 @@ int CTapDriver::Rx(BYTE *buf)
 	ASSERT(m_hTAP != -1);
 
 	// Check if there is data that can be received
-	if(!PendingPackets()){
+	if (!PendingPackets()) {
 		return 0;
 	}
 
@@ -473,11 +484,7 @@ int CTapDriver::Rx(BYTE *buf)
 		// We need to add the Frame Check Status (FCS) CRC back onto the end of the packet.
 		// The Linux network subsystem removes it, since most software apps shouldn't ever
 		// need it.
-
-		// Initialize the CRC
-		DWORD crc = crc32(0L, Z_NULL, 0);
-		// Calculate the CRC
-		crc = crc32(crc, buf, dwReceived);
+		int crc = crc32(buf, dwReceived);
 
 		buf[dwReceived + 0] = (BYTE)((crc >> 0) & 0xFF);
 		buf[dwReceived + 1] = (BYTE)((crc >> 8) & 0xFF);