rockbox: move firmware checksum algorithms into a common header

Before this was just implemented inline wherever it was needed. Now
it is provided as 2 inline functions in a header called checksum.h.
There should be no differences in actual behavior.

Change-Id: I5d756cc01dc6225f5cc8b6af90911a3fc7b57cd5

apps/plugins/crypt_firmware.c

@@ -36,8 +36,7 @@
 */
 
 #include "plugin.h"
-
-
+#include "checksum.h"
 
 static void aes_encrypt(void* data, uint32_t size)
 {
@@ -133,17 +132,6 @@ static void put_uint32be(unsigned char* buf, uint32_t x)
     buf[3] = x & 0xff;
 }
 
-static uint32_t calc_checksum(uint32_t sum, unsigned char* buf, int len)
-{
-   int i;
-
-   for (i = 0; i < len ; i++) {
-      sum += buf[i];
-   }
-
-   return sum;
-}
-
 enum plugin_status plugin_start(const void* parameter)
 {
     int fd;

apps/plugins/iriver_flash.c

@@ -23,6 +23,7 @@
  ****************************************************************************/
 #include "plugin.h"
 #include "lib/helper.h"
+#include "checksum.h"
 
 /*
  * Flash commands may rely on null pointer dereferences to work correctly.
@@ -395,7 +396,6 @@ static bool load_firmware(const char* filename, enum firmware firmware,
     {
         uint32_t checksum;
         uint8_t model[4];
-        uint32_t sum;
 
         /* subtract the header length */
         fd_len -= sizeof(checksum) + sizeof(model);
@@ -418,13 +418,8 @@ static bool load_firmware(const char* filename, enum firmware firmware,
             goto bail;
         }
 
-        /* calculate the checksum */
-        sum = MODEL_NUMBER;
-        for (off_t i = 0; i < fd_len; i++)
-            sum += buffer[i];
-
         /* verify the checksum */
-        if (sum != checksum)
+        if (!verify_checksum(checksum, buffer, fd_len))
         {
             msg = "Aborting: checksum mismatch";
             goto bail;

firmware/common/rb-loader.c

@@ -24,6 +24,7 @@
 #include "system.h"
 #include "file.h"
 #include "loader_strerror.h"
+#include "checksum.h"
 
 #if defined(HAVE_BOOTDATA)
 #include "bootdata.h"
@@ -129,8 +130,7 @@ static int load_firmware_filename(unsigned char* buf,
                                   int buffer_size)
 {
     int len;
-    unsigned long chksum, sum;
-    int i;
+    unsigned long chksum;
     int ret;
     int fd = open(filename, O_RDONLY);
 
@@ -162,14 +162,7 @@ static int load_firmware_filename(unsigned char* buf,
         goto end;
     }
 
-    sum = MODEL_NUMBER;
-
-    for(i = 0;i < len;i++)
-    {
-        sum += buf[i];
-    }
-
-    if (sum != chksum)
+    if (!verify_checksum(chksum, buf, len))
     {
         ret = EBAD_CHKSUM;
         goto end;

firmware/include/checksum.h

@@ -0,0 +1,41 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2020 James Buren
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ****************************************************************************/
+#include <stdint.h>
+#include <stdbool.h>
+
+#ifndef _CHECKSUM_H
+#define _CHECKSUM_H
+
+/* rockbox firmware checksum algorithm */
+static inline uint32_t calc_checksum(uint32_t sum, const uint8_t* buf, size_t len)
+{
+    for (size_t i = 0; i < len; i++)
+        sum += buf[i];
+    return sum;
+}
+
+/* similar to above but only used for verification */
+static inline bool verify_checksum(uint32_t cs, const uint8_t* buf, size_t len)
+{
+    return (calc_checksum(MODEL_NUMBER, buf, len) == cs);
+}
+
+#endif