1 files changed, 92 insertions, 0 deletions
diff --git a/tool/pagesig.c b/tool/pagesig.c
new file mode 100644
index 0000000..540c9d7
--- /dev/null
+++ b/tool/pagesig.c
@@ -0,0 +1,92 @@
+/*
+** 2013-10-01
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+******************************************************************************
+**
+** Compute hash signatures for every page of a database file.  This utility
+** program is useful for analyzing the output logs generated by the
+** ext/misc/vfslog.c extension.
+*/
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+#include <stdlib.h>
+
+/*
+** Compute signature for a block of content.
+**
+** For blocks of 16 or fewer bytes, the signature is just a hex dump of
+** the entire block.
+**
+** For blocks of more than 16 bytes, the signature is a hex dump of the
+** first 8 bytes followed by a 64-bit has of the entire block.
+*/
+static void vlogSignature(unsigned char *p, int n, char *zCksum){
+  unsigned int s0 = 0, s1 = 0;
+  unsigned int *pI;
+  int i;
+  if( n<=16 ){
+    for(i=0; i<n; i++) sprintf(zCksum+i*2, "%02x", p[i]);
+  }else{ 
+    pI = (unsigned int*)p;
+    for(i=0; i<n-7; i+=8){
+      s0 += pI[0] + s1;
+      s1 += pI[1] + s0;
+      pI += 2;
+    }
+    for(i=0; i<8; i++) sprintf(zCksum+i*2, "%02x", p[i]);
+    sprintf(zCksum+i*2, "-%08x%08x", s0, s1);
+  }
+}
+
+/*
+** Open a file.  Find its page size.  Read each page, and compute and
+** display the page signature.
+*/
+static void computeSigs(const char *zFilename){
+  FILE *in = fopen(zFilename, "rb");
+  unsigned pgsz;
+  size_t got;
+  unsigned n;
+  unsigned char aBuf[50];
+  unsigned char aPage[65536];
+
+  if( in==0 ){
+    fprintf(stderr, "cannot open \"%s\"\n", zFilename);
+    return;
+  }
+  got = fread(aBuf, 1, sizeof(aBuf), in);
+  if( got!=sizeof(aBuf) ){
+    goto endComputeSigs;
+  }
+  pgsz = aBuf[16]*256 + aBuf[17];
+  if( pgsz==1 ) pgsz = 65536;
+  if( (pgsz & (pgsz-1))!=0 ){
+    fprintf(stderr, "invalid page size: %02x%02x\n", aBuf[16], aBuf[17]);
+    goto endComputeSigs;
+  }
+  rewind(in);
+  for(n=1; (got=fread(aPage, 1, pgsz, in))==pgsz; n++){
+    vlogSignature(aPage, pgsz, aBuf);
+    printf("%4d: %s\n", n, aBuf);
+  }
+
+endComputeSigs:
+  fclose(in);
+}
+
+/*
+** Find page signatures for all named files.
+*/
+int main(int argc, char **argv){
+  int i;
+  for(i=1; i<argc; i++) computeSigs(argv[i]);
+  return 0;
+}