Re: [PATCH] mmap CRC

[Ben Stanley]

[EMAIL PROTECTED] wrote:

>On Tue, Nov 27, 2001 at 11:57:18PM +1100, Ben Stanley wrote:
>
>>Here is the mmap patch for calculating CRCs quickly.
>>
>
>How about wrapping #warnings in #ifdef __GNUC__?
>
Oh - I thought that was standard... :-)

If you insist, here's a new patch.

--- lyx-1.1.6fix3-orig/src/support/lyxsum.C     Wed Jun  6 02:07:10 2001
+++ lyx-1.1.6fix3/src/support/lyxsum.C  Wed Nov 28 00:57:55 2001
@@ -15,11 +15,41 @@
 
 #include <config.h>
 
+// Figure out what iterator implementation we are going to use...
+// This currently selects mmap over istreambuf_iterator.
+#ifdef HAVE_MMAP
+       #ifdef __GNUC__
+               #warning lyx::sum() using mmap (lightning fast but untested)
+       #endif
+       #define USE_MMAP
+#elif HAVE_DECL_ISTREAMBUF_ITERATOR
+       #ifdef __GNUC__
+               #warning lyx::sum() using istreambuf_iterator (fast)
+       #endif
+       #define USE_ISTREAMBUF_ITER
+       #define USE_STREAM
+#else
+       #ifdef __GNUC__
+               #warning lyx::sum() using istream_iterator (slow as a snail)
+       #endif
+       #define USE_ISTREAM_ITER
+       #define USE_STREAM
+#endif
+
+
 #include <fstream>
 #include <iterator>
 
 #include "support/lyxlib.h"
 
+#ifdef USE_MMAP
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/mman.h>
+#endif
+
 using std::ifstream;
 using std::ios;
 
@@ -104,23 +134,56 @@
 }
 
 
+
 // And this would be the file interface.
 unsigned long lyx::sum(string const & file)
 {
+
+#ifdef USE_STREAM
        std::ifstream ifs(file.c_str());
        if (!ifs) return 0;
-       
-#ifdef HAVE_DECL_ISTREAMBUF_ITERATOR
+#endif
+
+       // Setups
+
+#ifdef USE_ISTREAMBUF_ITER
        // This is a lot faster...
        std::istreambuf_iterator<char> beg(ifs);
        std::istreambuf_iterator<char> end;
-#else
+#endif
+
+#ifdef USE_ISTREAM_ITER
        // than this.
        ifs.unsetf(std::ios::skipws);
        std::istream_iterator<char> beg(ifs);
        std::istream_iterator<char> end;
 #endif
 
-       return do_crc(beg, end);
+#ifdef USE_MMAP
+       int fd = open(file.c_str(), O_RDONLY);
+       if( !fd ) return 0;
+       
+       struct stat info;
+       int st = fstat(fd, &info);
+       
+       void * mm = mmap(0, info.st_size, PROT_READ,
+                        MAP_PRIVATE /*| MAP_ANON*/, fd, 0); // MAP_ANON is not POSIX
+       if (mm == MAP_FAILED) {
+               close(fd);
+               return 0;
+       }
+       char *beg = (char*)mm;
+       char *end = ((char*)mm)+info.st_size;
+#endif
+
+       // Do the CRC
+       unsigned long result = do_crc(beg,end);
+
+       // Clean up
+#ifdef USE_MMAP
+       munmap( mm, info.st_size );
+       close(fd);
+#endif
+       return result;
 }