Cast problem

This is a discussion on Cast problem within the C Programming forums, part of the General Programming Boards category; Code: #define C64 unsigned long long C64 hash_rand() { C64 r = 0; unsigned long r1, r2= 0; for (unsigned ...

  1. #1
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    Post Cast problem

    Code:
    #define C64 unsigned long long
    
    C64 hash_rand() {
    	C64 r = 0;
    	unsigned long r1, r2= 0;
    
    	for (unsigned int i = 0; i < 32; ++i) {
    		r1 ^= rand() << i;
    		r2 ^= rand() << i;
    	}
            r = r1 | (C64) r2 << 32;
    	printf("R1=%ul R2=%ul Hash_rand=%ull\n",r1,r2,r);
    	return r;
    }
    A few result:
    Code:
    R1=687865691l R2=988029917l Hash_rand=687865691ll
    R1=591616934l R2=454174817l Hash_rand=591616934ll
    R1=930215157l R2=214394930l Hash_rand=930215157ll
    R1=2936190921l R2=1135713105l Hash_rand=2936190921ll
    R1=1256449038l R2=885147166l Hash_rand=1256449038ll
    R1=1912210059l R2=2292338960l Hash_rand=1912210059ll
    R1=1680048649l R2=2457515678l Hash_rand=1680048649ll
    R1=1436782960l R2=737207696l Hash_rand=1436782960ll
    R1=3008899124l R2=445239638l Hash_rand=3008899124ll
    R1=1501323191l R2=1232787536l Hash_rand=1501323191ll
    R1=1555984070l R2=213463547l Hash_rand=1555984070ll
    R1=278736328l R2=2676575472l Hash_rand=278736328ll
    R1=1041491509l R2=1880486007l Hash_rand=1041491509ll
    R1=2564025414l R2=3808829273l Hash_rand=2564025414ll
    R1=943291562l R2=3734505863l Hash_rand=943291562ll
    R1=1744278179l R2=3876748683l Hash_rand=1744278179ll
    R1=3977573745l R2=1631571305l Hash_rand=3977573745ll
    R1=2742987346l R2=1756414339l Hash_rand=2742987346ll
    Why I am not getting "hash_rand" as the combination of r1 and r2?
    thx
    FS

  2. #2
    Registered User C_ntua's Avatar
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    Well, don't know exactly what an unsigned long long is. I suppose it has 64bits? And your long have 32 bits?

    But in any case try this:

    Code:
    ..
    r =(C64) r1 | (C64) r2 << 32;
    ..
    So r1 is also casted to a C64. What you where doing is probably wrong. You do an | between a C64 (casted r2) and a ulong r1. Cast as I said and tell me

  3. #3
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    same problem. In fact the problem is not with (C64) r1, but with (C64)r2<<32 because this is 0 when assigned to r.
    if I replace that line with r = (C64) r2 << 32;
    I get 0 as result
    I suspect the problem is with my compiler, because I have seen other programs that make this cast without problem.

  4. #4
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    Quote Originally Posted by Kempelen View Post
    same problem. In fact the problem is not with (C64) r1, but with (C64)r2<<32 because this is 0 when assigned to r.
    if I replace that line with r = (C64) r2 << 32;
    I get 0 as result
    I suspect the problem is with my compiler, because I have seen other programs that make this cast without problem.
    You will probably find that it works if you do
    Code:
    r = (C64)r2 << (C64)32;
    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  5. #5
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    no, good try but it doesnt work

  6. #6
    Registered User C_ntua's Avatar
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    Are you sure the C64 type you have is a 64bit variable? I test it and it tells me it is a 32bit variable. That is why r = (C64) r2 << 32; gives zero. If it was 64bit then it should not give zero.

    Try printf("%d", sizeof(C64));

    By the way!
    Does %ull exist for printf() ?? I think it doesn't.
    Look at your results. Everything ends with a l. That is not a "1" but an "l" propably!

  7. #7
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    Right, if you are using windows and gcc mingw, you need to use the %I64u rather than %ull - this can be seen by the fact that your number is showing with an extra l on the end [it would be more noticeable if you used %ULL, as L is more different 1 than a l.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  8. #8
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    I change the program for this one:

    Code:
    #define C64 unsigned long long
    #define putBitTo1(x,y)		((x) |= ((BITBOARD) 1) << (y));
    
    C64 hash_rand() {
    	C64 r = 0;
    
    	for (unsigned int i = 0; i < 64; ++i) {
                  if (rand()%2)
                     putBitTo0(r,i);
    	}
    	return r;
    }
    And this Works!!!!.
    Don't know where the problem is, but has a workaround

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