C / C++ / MFC

DQNOK wrote:

I'm looking to fill memory with a pattern...

//author: David Qualls
//date:   Sept 2007
#include <string.h>

void memoryfill( void* target, char* pattern, size_t ptrnlen, size_t numRepeats )
{  
   char* trgt = (char*)target;  //for ease in pointer manipulation.
   if( 0 == numRepeats ) 
   {
      ; // do nothing!
   }
   else if( 1 == ptrnlen ) 
   {
      memset(target, *pattern, numRepeats);   
   }
   else    
   {
   // The naive approach here would be:
   // while( numRepeats--  > 0 )
   // {  memcpy(target, pattern, ptrnlen);
   //    (char*)target += ptrnlen;
   // }
   // But this is O(numRepeats).  Very ineffecient for large numRepeats.
   // Use a binary algorithm instead.  This one uses between log(numRepeats)
   // and 2*log(numRepeats) calls to memcpy(); a maximum of 64 calls to 
   // memcpy()for 32-bit size_t's : versus up to 4-billion calls to memcpy().

   // First, fill target up to the highest "bit" of repeatCount. log(n) loops.
      memcpy(trgt, pattern, ptrnlen); //begin by putting one copy into target.
      int snglbit=1;                  //number of copies in target. Always a power of 2.
      int thisCnt = numRepeats >> 1;  //one bit of repeatCount has already been taken care of.
      while( thisCnt > 0 )            //until all bits have been shifted off.
      {
         memcpy(trgt+ptrnlen*snglbit, trgt, ptrnlen*snglbit); //now double the amount in target.
         snglbit <<= 1;  //doubles the value of snglbit.
         thisCnt >>= 1;  //halves the value of thisCnt.
      }
   // snglbit now matches the most significant bit of repeatCount.
      char* endptr = trgt + ptrnlen*snglbit;   //where the next memcpy target is.
      while( (snglbit >>= 1) > 0 )             //for each lower bit within numRepeats,
      {
         if( snglbit & numRepeats )            //if this bit is ON within numRepeats,
         {
            memcpy(endptr, trgt, ptrnlen*snglbit);
            endptr += ptrnlen*snglbit;
         }
      }
   }
   return;
}
<br>
#include <stdio.h>
<br>
int main()
{
   char buf[1024];
   memset(buf, 0, 1024);  //insure null terminator(s)
   memoryfill( buf, "Hello World_", 12, 19 );
   printf("\n%s", buf);
}

DQNOK wrote:

Interesting! Clever idea.

Mark Salsbery wrote:

Standard scrollbars use the system metrics settings.

tortexy wrote:

If I do MoveWindow or SetWindowPos, the width may change but the arrow will become flat

tortexy wrote:

which scrollbars are you referring to? The ones subclassed with CScrollbar? /not part of any control/

Mark Salsbery
Microsoft MVP - Visual C++