From 7f749b4689dfb212580abbd568818e95a922fe49 Mon Sep 17 00:00:00 2001
From: Björn Stenberg <bjorn@haxx.se>
Date: Thu, 8 Jan 2004 00:22:27 +0000
Subject: Added support for multimedia .ajz files

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@4199 a1c6a512-1295-4272-9138-f99709370657
---
 tools/descramble.c | 105 ++++++++++++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 95 insertions(+), 10 deletions(-)

diff --git a/tools/descramble.c b/tools/descramble.c
index d28e18a951..8ba8d4a18f 100644
--- a/tools/descramble.c
+++ b/tools/descramble.c
@@ -26,11 +26,14 @@ int main (int argc, char** argv)
     unsigned char *inbuf,*outbuf;
     unsigned char *iname = argv[1];
     unsigned char *oname = argv[2];
+    unsigned char header[32];
     int headerlen = 6;
+    int descramble = 1;
     FILE* file;
 
     if (argc < 3) {
-       printf("usage: %s [-fm] [-v2] <input file> <output file>\n",argv[0]);
+       printf("usage: %s [-fm] [-v2] [-mm] <input file> <output file>\n",
+              argv[0]);
        return -1;
     }
 
@@ -39,6 +42,13 @@ int main (int argc, char** argv)
         iname = argv[2];
         oname = argv[3];
     }
+
+    if (!strcmp(argv[1], "-mm")) {
+        headerlen = 16;
+        iname = argv[2];
+        oname = argv[3];
+        descramble = 0;
+    }
     
     /* open file and check size */
     file = fopen(iname,"rb");
@@ -48,7 +58,13 @@ int main (int argc, char** argv)
     }
     fseek(file,0,SEEK_END);
     length = ftell(file) - headerlen; /* skip header */
-    fseek(file,headerlen,SEEK_SET); 
+    fseek(file,0,SEEK_SET);
+    i = fread(header, 1, headerlen, file);
+    if ( !i ) {
+       perror(iname);
+       return -1;
+    }
+    
     inbuf = malloc(length);
     outbuf = malloc(length);
     if ( !inbuf || !outbuf ) {
@@ -64,15 +80,84 @@ int main (int argc, char** argv)
     }
     fclose(file);
 
-    /* descramble */
-    slen = length/4;
-    for (i = 0; i < length; i++) {
-      unsigned long addr = ((i % slen) << 2) + i/slen;
-      unsigned char data = inbuf[i];
-      data = ~((data >> 1) | ((data << 7) & 0x80)); /* poor man's ROR */
-      outbuf[addr] = data;
+    if (descramble) {
+        /* descramble */
+        slen = length/4;
+        for (i = 0; i < length; i++) {
+            unsigned long addr = ((i % slen) << 2) + i/slen;
+            unsigned char data = inbuf[i];
+            data = ~((data >> 1) | ((data << 7) & 0x80)); /* poor man's ROR */
+            outbuf[addr] = data;
+        }
     }
-    
+    else {
+        void* tmpptr;
+        unsigned int j=0;
+        int stringlen = 32;
+        int unpackedsize;
+        unsigned char xorstring[32];
+
+        unpackedsize = ((unsigned int*)header)[1];
+        length = ((unsigned int*)header)[2];
+
+        /* calculate the xor string used */
+        for (i=0; i<stringlen; i++) {
+            int top=0, topchar=0, c;
+            int bytecount[256];
+            memset(bytecount, 0, sizeof(bytecount));
+
+            /* gather byte frequency statistics */
+            for (c=i; c<length; c+=stringlen)
+                bytecount[inbuf[c]]++;
+
+            /* find the most frequent byte */
+            for (c=0; c<256; c++) {
+                if (bytecount[c] > top) {
+                    top = bytecount[c];
+                    topchar = c;
+                }
+            }
+            xorstring[i] = topchar;
+        }
+        printf("XOR string: %.*s\n", stringlen, xorstring);
+        
+        /* xor the buffer */
+        for (i=0; i<length; i++)
+            outbuf[i] = inbuf[i] ^ xorstring[i & (stringlen-1)];
+
+        /* unpack */
+        tmpptr = realloc(inbuf, unpackedsize);
+        memset(tmpptr, 0, unpackedsize);
+        inbuf = outbuf;
+        outbuf = tmpptr;
+
+        for (i=0; i<length;) {
+            int bit;
+            int head = inbuf[i++];
+
+            for (bit=0; bit<8 && i<length; bit++) {
+                if (head & (1 << (bit))) {
+                    outbuf[j++] = inbuf[i++];
+                }
+                else {
+                    int x;
+                    int byte1 = inbuf[i];
+                    int byte2 = inbuf[i+1];
+                    int count = (byte2 & 0x0f) + 3;
+                    int src =
+                        (j & 0xfffff000) + (byte1 | ((byte2 & 0xf0)<<4)) + 18;
+                    if (src > j)
+                        src -= 0x1000;
+
+                    for (x=0; x<count; x++)
+                        outbuf[j++] = outbuf[src+x];
+                    i += 2;
+                }
+            }
+        }
+        length = j;
+    }
+
     /* write file */
     file = fopen(oname,"wb");
     if ( !file ) {
-- 
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