From: drh <drh@noemail.net>
Date: Wed, 19 May 2010 18:08:10 +0000 (+0000)
Subject: Revise the checksumming algorithm in wal.c.  More variable refactoring.
X-Git-Tag: version-3.7.2~362
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=584c754d6516558e7ed2a185c8d9092274d12282;p=thirdparty%2Fsqlite.git

Revise the checksumming algorithm in wal.c.  More variable refactoring.

FossilOrigin-Name: 542b90eba6440a0bccef329788fd17a2d3fbeee6
---

diff --git a/manifest b/manifest
index c964b500ff..df01a9717f 100644
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Refactoring\ssome\svariable\snames\sin\swal.c.
-D 2010-05-19T17:49:50
+C Revise\sthe\schecksumming\salgorithm\sin\swal.c.\s\sMore\svariable\srefactoring.
+D 2010-05-19T18:08:11
 F Makefile.arm-wince-mingw32ce-gcc fcd5e9cd67fe88836360bb4f9ef4cb7f8e2fb5a0
 F Makefile.in a5cad1f8f3e021356bfcc6c77dc16f6f1952bbc3
 F Makefile.linux-gcc d53183f4aa6a9192d249731c90dbdffbd2c68654
@@ -227,7 +227,7 @@ F src/vdbeblob.c 5327132a42a91e8b7acfb60b9d2c3b1c5c863e0e
 F src/vdbemem.c 2a82f455f6ca6f78b59fb312f96054c04ae0ead1
 F src/vdbetrace.c 864cef96919323482ebd9986f2132435115e9cc2
 F src/vtab.c a0f8a40274e4261696ef57aa806de2776ab72cda
-F src/wal.c 105bad789a23a495fe134f5ef9dac6d8c06f971d
+F src/wal.c 5fd5853973652f8a8d81ab1ab7577559f46f3622
 F src/wal.h 434f76f51225bb614e43ccb6bd2341541ba6a06e
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c 75fee9e255b62f773fcadd1d1f25b6f63ac7a356
@@ -816,14 +816,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
-P a71a22b52f4570e934063553a81b39268127dc44
-R 1c999fd53b1df4ca8173c8fb4d6b6989
+P 1d201ff51f7c5ecdf71a91ed25204b7130894282
+R d0346b793d27da12b31b3a8952af1c86
 U drh
-Z cc4a12a1a16f8ebec7597d63ade72388
+Z 747ef9a34e0e8619bf7584ee288d56f6
 -----BEGIN PGP SIGNATURE-----
 Version: GnuPG v1.4.6 (GNU/Linux)
 
-iD8DBQFL9CTBoxKgR168RlERAlCKAJ4zOxPBD9LXWpD6J1dW7wmEg9tn5QCfTw1j
-bOeNi5aQREq9/zvmCMu2nsA=
-=EdxO
+iD8DBQFL9CkOoxKgR168RlERApEDAJ9DtZ/mpw6bX3TwJ7fVkL3EMPB9pACdF5w5
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+=YSri
 -----END PGP SIGNATURE-----
diff --git a/manifest.uuid b/manifest.uuid
index 2826d32ea4..d9a6bdd59e 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-1d201ff51f7c5ecdf71a91ed25204b7130894282
\ No newline at end of file
+542b90eba6440a0bccef329788fd17a2d3fbeee6
\ No newline at end of file
diff --git a/src/wal.c b/src/wal.c
index eb5e2e4de9..1f90ce7267 100644
--- a/src/wal.c
+++ b/src/wal.c
@@ -270,49 +270,24 @@ struct WalIterator {
 
 /*
 ** Generate an 8 byte checksum based on the data in array aByte[] and the
-** initial values of aCksum[0] and aCksum[1]. The checksum is written into
-** aCksum[] before returning.
-**
-** The range of bytes to checksum is treated as an array of 32-bit 
-** little-endian unsigned integers. For each integer X in the array, from
-** start to finish, do the following:
-**
-**   aCksum[0] += X;
-**   aCksum[1] += aCksum[0];
-**
-** For the calculation above, use 64-bit unsigned accumulators. Before
-** returning, truncate the values to 32-bits as follows: 
-**
-**   aCksum[0] = (u32)(aCksum[0] + (aCksum[0]>>24));
-**   aCksum[1] = (u32)(aCksum[1] + (aCksum[1]>>24));
+** initial values of aCksum[0] and aCksum[1]. The checksum is written 
+** back into aCksum[] before returning.
 */
-static void walChecksumBytes(u8 *aByte, int nByte, u32 *aCksum){
-  u64 sum1 = aCksum[0];
-  u64 sum2 = aCksum[1];
-  u32 *a32 = (u32 *)aByte;
-  u32 *aEnd = (u32 *)&aByte[nByte];
+static void walChecksumBytes(u8 *a, int nByte, u32 *aCksum){
+  u32 s1 = aCksum[0];
+  u32 s2 = aCksum[1];
+  u8 *aEnd = (u8*)&a[nByte];
 
+  assert( nByte>=8 );
   assert( (nByte&0x00000003)==0 );
 
-  if( SQLITE_LITTLEENDIAN ){
-#ifdef SQLITE_DEBUG
-    u8 *a = (u8 *)a32;
-    assert( *a32==(a[0] + (a[1]<<8) + (a[2]<<16) + (a[3]<<24)) );
-#endif
-    do {
-      sum1 += *a32;
-      sum2 += sum1;
-    } while( ++a32<aEnd );
-  }else{
-    do {
-      u8 *a = (u8*)a32;
-      sum1 += a[0] + (a[1]<<8) + (a[2]<<16) + (a[3]<<24);
-      sum2 += sum1;
-    } while( ++a32<aEnd );
-  }
-
-  aCksum[0] = sum1 + (sum1>>24);
-  aCksum[1] = sum2 + (sum2>>24);
+  do {
+    s1 += (a[0]<<24) + (a[2]<<16) + (a[2]<<8) + a[3] + s2;
+    s2 += (a[3]<<24) + (a[5]<<16) + (a[6]<<8) + a[7] + s1;
+    a += 8;
+  }while( a<aEnd );
+  aCksum[0] = s1;
+  aCksum[1] = s2;
 }
 
 /*
@@ -645,7 +620,7 @@ static int walIndexRecover(Wal *pWal){
   if( nSize>WAL_FRAME_HDRSIZE ){
     u8 aBuf[WAL_FRAME_HDRSIZE];   /* Buffer to load first frame header into */
     u8 *aFrame = 0;               /* Malloc'd buffer to load entire frame */
-    int nFrame;                   /* Number of bytes at aFrame */
+    int szFrame;                  /* Number of bytes in buffer aFrame[] */
     u8 *aData;                    /* Pointer to data part of aFrame buffer */
     int iFrame;                   /* Index of last frame read */
     i64 iOffset;                  /* Next offset to read from log file */
@@ -671,8 +646,8 @@ static int walIndexRecover(Wal *pWal){
     aCksum[1] = sqlite3Get4byte(&aBuf[8]);
 
     /* Malloc a buffer to read frames into. */
-    nFrame = szPage + WAL_FRAME_HDRSIZE;
-    aFrame = (u8 *)sqlite3_malloc(nFrame);
+    szFrame = szPage + WAL_FRAME_HDRSIZE;
+    aFrame = (u8 *)sqlite3_malloc(szFrame);
     if( !aFrame ){
       return SQLITE_NOMEM;
     }
@@ -680,13 +655,13 @@ static int walIndexRecover(Wal *pWal){
 
     /* Read all frames from the log file. */
     iFrame = 0;
-    for(iOffset=WAL_HDRSIZE; (iOffset+nFrame)<=nSize; iOffset+=nFrame){
+    for(iOffset=WAL_HDRSIZE; (iOffset+szFrame)<=nSize; iOffset+=szFrame){
       u32 pgno;                   /* Database page number for frame */
       u32 nTruncate;              /* dbsize field from frame header */
       int isValid;                /* True if this frame is valid */
 
       /* Read and decode the next log frame. */
-      rc = sqlite3OsRead(pWal->pWalFd, aFrame, nFrame, iOffset);
+      rc = sqlite3OsRead(pWal->pWalFd, aFrame, szFrame, iOffset);
       if( rc!=SQLITE_OK ) break;
       isValid = walDecodeFrame(aCksum, &pgno, &nTruncate, szPage, aData, aFrame);
       if( !isValid ) break;