[libdvdcss-devel] Read in advance 50 sectors during CSS key computation, in order to reduce number of read access

[David Dielsky]

libdvdcss | branch: master | David Dielsky <david122192 at gmail.com> | Tue Apr  8 23:29:53 2014 +0200| [d14eee3198f9733ea8e68a136ca278d4c7bb598b] | committer: Jean-Baptiste Kempf

Read in advance 50 sectors during CSS key computation, in order to reduce number of read access

> http://git.videolan.org/gitweb.cgi/libdvdcss.git/?a=commit;h=d14eee3198f9733ea8e68a136ca278d4c7bb598b
---

 src/css.c |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/src/css.c b/src/css.c
index 5aeae86..4e1e756 100644
--- a/src/css.c
+++ b/src/css.c
@@ -62,6 +62,7 @@
 #include "device.h"
 
 #define PSZ_KEY_SIZE (KEY_SIZE * 3)
+#define BLOCK_BUFFER_SIZE 50
 
 /*****************************************************************************
  * Local prototypes
@@ -1498,6 +1499,10 @@ static int CrackTitleKey( dvdcss_t dvdcss, int i_pos, int i_len,
     i_tries = 0;
     i_success = 0;
 
+    /* Read in advance 50 sectors in a buffer, to reduce the number of read access */
+    int nb_sectors = BLOCK_BUFFER_SIZE;
+    void* p_read_buffer = malloc( nb_sectors * DVDCSS_BLOCK_SIZE );
+
     do
     {
         i_ret = dvdcss->pf_seek( dvdcss, i_pos );
@@ -1507,6 +1512,13 @@ static int CrackTitleKey( dvdcss_t dvdcss, int i_pos, int i_len,
             print_error( dvdcss, "seek failed" );
         }
 
+        /* every BLOCK_BUFFER_SIZE sectors, read BLOCK_BUFFER_SIZE sectors more */
+        if ( ( i_reads % nb_sectors == 0 ) && p_read_buffer )
+        {
+            dvdcss_read(dvdcss, p_read_buffer, nb_sectors, DVDCSS_NOFLAGS);
+            dvdcss->pf_seek( dvdcss, i_pos );
+        }
+
         i_ret = dvdcss_read( dvdcss, p_buf, 1, DVDCSS_NOFLAGS );
 
         /* Either we are at the end of the physical device or the auth
@@ -1585,6 +1597,8 @@ static int CrackTitleKey( dvdcss_t dvdcss, int i_pos, int i_len,
         print_debug( dvdcss, "end of title reached" );
     }
 
+    free( p_read_buffer );
+
     /* Print some statistics. */
     print_debug( dvdcss, "successful attempts %d/%d, scrambled blocks %d/%d",
                          i_success, i_tries, i_encrypted, i_reads );