adler32: import adapted implementation from tinf/zlib

This adds an adapted version of the adler32 algorithm from tinf/zlib
which will be necessary to support ZLIB deflate streams in the future.

Change-Id: Ie60e15acb288acf56a2d44e3d3e912e1b3eb2216

firmware/SOURCES

@@ -269,6 +269,7 @@ common/timefuncs.c
 common/unicode.c
 common/vuprintf.c
 common/zip.c
+common/adler32.c
 
 /* Display */
 scroll_engine.c

firmware/common/adler32.c

@@ -0,0 +1,75 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2021 James Buren (adaptations from tinf/zlib)
+ *
+ * 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 "adler32.h"
+#include "system.h"
+
+/* adler_32 (derived from tinf adler32 which was taken from zlib)
+ * Adler-32 algorithm taken from the zlib source, which is
+ * Copyright (C) 1995-1998 Jean-loup Gailly and Mark Adler
+ */
+uint32_t adler_32(const void *src, uint32_t len, uint32_t adler32)
+{
+    const unsigned char *buf = (const unsigned char *)src;
+    uint32_t s1 = (adler32 & 0xffff);
+    uint32_t s2 = (adler32 >> 16);
+
+    enum {
+        A32_BASE = 65521,
+        A32_NMAX = 5552,
+    };
+
+    while (len > 0) {
+        uint32_t k = MIN(len, A32_NMAX);
+        uint32_t i;
+
+        for (i = k / 16; i; --i, buf += 16) {
+            s2 += s1 += buf[0];
+            s2 += s1 += buf[1];
+            s2 += s1 += buf[2];
+            s2 += s1 += buf[3];
+            s2 += s1 += buf[4];
+            s2 += s1 += buf[5];
+            s2 += s1 += buf[6];
+            s2 += s1 += buf[7];
+            s2 += s1 += buf[8];
+            s2 += s1 += buf[9];
+            s2 += s1 += buf[10];
+            s2 += s1 += buf[11];
+            s2 += s1 += buf[12];
+            s2 += s1 += buf[13];
+            s2 += s1 += buf[14];
+            s2 += s1 += buf[15];
+        }
+
+        for (i = k % 16; i; --i) {
+            s1 += *buf++;
+            s2 += s1;
+        }
+
+        s1 %= A32_BASE;
+        s2 %= A32_BASE;
+
+        len -= k;
+    }
+
+    return (s1 | (s2 << 16));
+}

firmware/include/adler32.h

@@ -0,0 +1,29 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
+ *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
+ *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
+ *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
+ *                     \/            \/     \/    \/            \/
+ * $Id$
+ *
+ * Copyright (C) 2021 James Buren (adaptations from tinf/zlib)
+ *
+ * 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>
+
+#ifndef _ADLER32_H
+#define _ADLER32_H
+
+uint32_t adler_32(const void *src, uint32_t len, uint32_t adler32);
+
+#endif