Initial Commit

Signed-off-by: Marc <foxtrot@malloc.me>

1 files changed, 63 insertions, 0 deletions

@@ -0,0 +1,63 @@
+/* Copyright 2021 The libwifi Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "crc.h"
+#include "../misc/byteswap.h"
+
+#include <stdint.h>
+#include <sys/types.h>
+
+/*
+ * Basic CRC32 implementation for getting the frame check sum of
+ * a supplied message, usually frame data.
+ */
+uint32_t libwifi_crc32(const unsigned char *message, int message_len) {
+    int i, j;
+    unsigned int byte, crc, mask;
+    i = 0;
+    crc = 0xFFFFFFFF;
+    while (i < message_len) {
+        byte = message[i];
+        crc = crc ^ byte;
+        for (j = 7; j >= 0; j--) {
+            mask = -(crc & 1);
+            crc = (crc >> 1) ^ (0xEDB88320 & mask);
+        }
+        i = i + 1;
+    }
+    return ~crc;
+}
+
+/*
+ * Specific function for calculating a frame FCS, byteswapped for the
+ * host endianess.
+ */
+uint32_t libwifi_calculate_fcs(const unsigned char *frame, size_t frame_len) {
+    return BYTESWAP32(libwifi_crc32(frame, frame_len));
+}
+
+/*
+ * Verify a frame containing a FCS at the end to the FCS calculated
+ * by libwifi.
+ */
+int libwifi_frame_verify(void *frame, size_t frame_len) {
+    uint32_t oCRC = *((uint32_t *) ((char *) frame + frame_len));
+    uint32_t rCRC = libwifi_calculate_fcs(frame, frame_len);
+
+    if (rCRC == oCRC) {
+        return 1;
+    }
+    return 0;
+}