Re: TextOut() to a DialogBox ???

From:
"Peter Olcott" <NoSpam@OCR4Screen.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Wed, 24 Mar 2010 19:34:51 -0500
Message-ID:
<0YmdnXNrsfoxMjfWnZ2dnUVZ_oadnZ2d@giganews.com>
"Geoff" <geoff@invalid.invalid> wrote in message
news:qf5lq556kt4oh22dq12c73sp161ogbgqgr@4ax.com...

On Wed, 24 Mar 2010 15:39:26 -0500, "Peter Olcott"
<NoSpam@OCR4Screen.com> wrote:

Here is an interesting note that I don't understand. A
slight revision (to make it a little less CPU intensive,
thus more memory intensive) only actually achieves 21 MB
per
second of the 12 GB / second maximum RAM speed. (RAM
speed
reported by MemTest86).

const uint32 size = 100000000;
std::vector<uint32> Data;
uint32 Max = 0x3fffffff;

void Process() {
 clock_t finish;
 clock_t start = clock();
 double duration;
 uint32 num;
   for (uint32 N = 0; N < Max; N++)
     num = Data[num];
  finish = clock();
  duration = (double)(finish - start) / CLOCKS_PER_SEC;
  printf("%4.2f Seconds\n", duration);
}

Another thing that I don't understand is that it crashes
when
     num = Data[num];
is replaced by
     num = Data[N];


Two bugs exist.

1. You never initialize num, so executing num = Data[num]
will access
a garbage address in debug mode and will attempt to read
Data[0] in
release mode since the OS will zero-fill num for you.


Right

2. You never resize the vector space "Data" before you
attempt to
access it.

Data.resize(Max);


Wrong. (reserve() has almost the same effect as resize() )

int main() {
  printf("Size in bytes--->%d\n", size * 4);
  Data.reserve(size);
  for (uint32 N = 0; N < size; N++) {
    uint32 Random = rand() * rand();
    Random %= size;
    Data.push_back( Random );
  }

  char N;
  printf("Hit any key to Continue:");
  scanf("%c", &N);

  Process();

 return 0;
}

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