From patchwork Tue Jan  3 13:35:38 2012
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Subject: [v5, 2/9] Add rle_encode and rle_decode functions Implement Run Length
 Encoding compression
From: Orit Wasserman <owasserm@redhat.com>
X-Patchwork-Id: 134095
Message-Id: <1325597745-29293-3-git-send-email-owasserm@redhat.com>
To: qemu-devel@nongnu.org
Cc: blauwirbel@gmail.com, stefanha@gmail.com,
 Orit Wasserman <owasserm@redhat.com>, quintela@redhat.com
Date: Tue,  3 Jan 2012 15:35:38 +0200

Signed-off-by: Orit Wasserman <owasserm@redhat.com>

---
arch_init.c |   58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 58 insertions(+), 0 deletions(-)

diff --git a/arch_init.c b/arch_init.c
index fdda277..426b34d 100644
--- a/arch_init.c
+++ b/arch_init.c
@@ -139,6 +139,9 @@ typedef struct XBRLEHeader {
     uint32_t xh_cksum;
 } XBRLEHeader;
 
+static int rle_encode(uint8_t *src, int slen, uint8_t *dst, int dlen);
+static int rle_decode(uint8_t *src, int slen, uint8_t *dst, int dlen);
+
 /***********************************************************/
 /* XBRLE page cache implementation */
 static CacheItem *cache_item_get(unsigned long pos, int item)
@@ -277,6 +280,61 @@ static void cache_insert(unsigned long addr, uint8_t *pdata)
     it->it_addr = addr;
 }
 
+/* XBRLE (Xor Based Run-Length Encoding) */
+static int rle_encode(uint8_t *src, int slen, uint8_t *dst, int dlen)
+{
+    int d = 0, ch_run = 0, i;
+    uint8_t prev = 0, ch = 0;
+
+    for (i = 0; i <= slen; i++) {
+        if (i != slen) {
+            ch = src[i];
+        }
+
+        if (!i || (i != slen && ch == prev && ch_run < 255)) {
+            ch_run++;
+        } else {
+            if (d+2 > dlen) {
+                return -1;
+            }
+            *dst++ = ch_run;
+            *dst++ = prev;
+            d += 2;
+            ch_run = 1;
+        }
+
+        prev = ch;
+    }
+    return d;
+}
+
+static int rle_decode(uint8_t *src, int slen, uint8_t *dst, int dlen)
+{
+    int d = 0, s;
+
+    for (s = 0; s < slen-1; s += 2) {
+        uint8_t ch_run = src[s];
+        uint8_t ch = src[s+1];
+        while (ch_run--) {
+            if (d == dlen) {
+                return -1;
+            }
+            dst[d] = ch;
+            d++;
+        }
+    }
+    return d;
+}
+
+static void xor_encode(uint8_t *dst, uint8_t *src1, uint8_t *src2)
+{
+    int i;
+
+    for (i = 0; i < TARGET_PAGE_SIZE; i++) {
+        dst[i] = src1[i] ^ src2[i];
+    }
+}
+
 static int is_dup_page(uint8_t *page, uint8_t ch)
 {
     uint32_t val = ch << 24 | ch << 16 | ch << 8 | ch;