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C puzzles

gowrikumar.com

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Re: C puzzles

#3

Post by CapacitorSet »

I really dislike his choice of coding style. Compare:

  int CountBits (unsigned int x )
  {
      static unsigned int mask[] = { 0x55555555,
          0x33333333,
          0x0F0F0F0F,
          0x00FF00FF,
          0x0000FFFF
          } ;

          int i ;
          int shift ; /* Number of positions to shift to right*/
          for ( i =0, shift =1; i > shift) & mask[i]);
          return x;
  }
as opposed to:

  int countBits (unsigned int x) {
    static unsigned int mask[] = {
      0x55555555,
      0x33333333,
      0x0F0F0F0F,
      0x00FF00FF,
      0x0000FFFF
    };

    int i;
    int shift; // Number of positions to shift to the right
    for (i = 0, shift = 1; i > shift) & mask[i]);
    return x;
  }

Re: C puzzles

#4

Post by GrinningFool »

Fun stuff , thanks for posting it. I've been getting back into C lately, iterating through implementing common algorithms from scratch.

In spite of the kinds of easy to make mistakes that are highlighted on the site, I'm finding it to be a lot of fun - not having my hand held by frameworks that try to stop me from shooting myself in a foot is refreshing and brings back that feeling of "I can build whatever the hell I want in whatever f'd up way I want" that C always held for me.

Too, in the years since I've last done something like this, I've learned a lot - so he process is made better by applying ideas I've internalized to old problems, measuring effects on performance, etc.

Core dumps are a thing that I can cause without triggering some kind of obscure runtime bug and it's oddly exciting.

Re: C puzzles

#5

Post by zerocrates »

CapacitorSet wrote: post #3

I really dislike his choice of coding style. Compare: int CountBits (unsigned int x ) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x00FF00FF, 0x0000FFFF } ; int i ; int shift ; /* Number of positions to shift to right*/ for ( i =0, shift =1; i > shift) & mask[i]); return x; } as opposed to: int countBits (unsigned int x) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x0…

I was about to say I didn't think it made a big difference but I have no idea what's going on with that intraline whitespace.

Re: C puzzles

#6

Post by Cyph0n »

zerocrates wrote: post #5
CapacitorSet wrote: post #3

I really dislike his choice of coding style. Compare: int CountBits (unsigned int x ) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x00FF00FF, 0x0000FFFF } ; int i ; int shift ; /* Number of positions to shift to right*/ for ( i =0, shift =1; i > shift) & mask[i]); return x; } as opposed to: int countBits (unsigned int x) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x0…

I was about to say I didn't think it made a big difference but I have no idea what's going on with that intraline whitespace.

If I saw this in a codebase, I'd assume the programmer's fingers slipped a lot.

Re: C puzzles

#8

Post by 0xmohit »

I'd have called it "gotchas" or "puzzlers" instead of "puzzles".

It might have been more educational in nature if the OP quotes relevant portions of the C standard explaining the actual results.

Re: C puzzles

#9

Post by CapacitorSet »

zerocrates wrote: post #5
CapacitorSet wrote: post #3

I really dislike his choice of coding style. Compare: int CountBits (unsigned int x ) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x00FF00FF, 0x0000FFFF } ; int i ; int shift ; /* Number of positions to shift to right*/ for ( i =0, shift =1; i > shift) & mask[i]); return x; } as opposed to: int countBits (unsigned int x) { static unsigned int mask[] = { 0x55555555, 0x33333333, 0x0F0F0F0F, 0x0…

I was about to say I didn't think it made a big difference but I have no idea what's going on with that intraline whitespace.

To me, having consistent indentation does make a substantial difference - it is fundamental to understand at a glance what structures are present in the code, rather than "parsing" it in detail every time I'm looking for something.
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