Wishlist Item

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choibakk
Posts: 19
Joined: 5 Sep 2019 19:30

Wishlist Item

Unread post by choibakk » 22 May 2020 2:58

Hi Thomas, tried to email you but could not directly. Since you helped me with external functions [in an eallier support post for those that are looking] (to overcome a multiplication overflow when the overflow is desired) I have added a few more functions to my external "C" DLL, which makes me love VP even more--seriously. So a wish list predicate if you get the chance sometime in the future:

In "pfc\memory\bit.cl" you have:

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predicates     trailingZeroBits : (unsigned Value) -> unsigned Count.     % @short Calculating the number of consecutive low-order zeros     % @end
which is exactly what I needed, but it only supports unsigned, so I was using trailingZeroBits on the LOW/HI 32 bits and using mkUnsigned64 to put it back together to handle 64-bit unsigned integers. It would be great to have a 64 bit version of trailingZeroBits. In the interim, I added the following to my external "C" DLL for performance:
unsigned char APIENTRY Ls1b(UINT64 bits, UINT64* bitsOut, unsigned char* index)
{
unsigned long uint64 = 0;
unsigned char result = _BitScanForward64(&uint64, bits);
*index = (unsigned char)uint64;
if(bitsOut!=nullptr)
*bitsOut = bits ^ (1ULL << *index);
return result;
}
PS: The _BitScanForward64 is the relevant function and is a compiler intrinsic function in Visual Studio C++.

Thanks for all your hard work!

Martin Meyer
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Posts: 280
Joined: 14 Nov 2002 0:01

Re: Wishlist Item

Unread post by Martin Meyer » 22 May 2020 15:15

Hi choibakk,

Wikipedia gives instructions how you can code a trailingZeroBits/1-> function for 64 bits:

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constants     m1 : unsigned64 = 0x5555555555555555.     m2 : unsigned64 = 0x3333333333333333.     m4 : unsigned64 = 0x0F0F0F0F0F0F0F0F.   class predicates     bitCount64 : (unsigned64 Value) -> unsigned64 Count. clauses     bitCount64(Value) = Counter5 ** 0x7F :-         Counter0 = Value - (Value >> 1 ** m1),         Counter1 = (Counter0 ** m2) + (Counter0 >> 2 ** m2),         Counter2 = Counter1 + (Counter1 >> 4) ** m4,         Counter3 = Counter2 + (Counter2 >> 8),         Counter4 = Counter3 + (Counter3 >> 16),         Counter5 = Counter4 + (Counter4 >> 32).   class predicates     trailingZeroBits64 : (unsigned64 Value) -> unsigned64 Count. clauses     trailingZeroBits64(Value) = if 0 = Value then sizeBitsOf(unsigned64) else bitCount64(Value - 1 ** ~~Value) end if.
Regards Martin

Martin Meyer
VIP Member
Posts: 280
Joined: 14 Nov 2002 0:01

Re: Wishlist Item

Unread post by Martin Meyer » 22 May 2020 17:26

I recommend however that you keep using the old style syntax for bitwise and boolean operators in build 905. The new syntax has an issue in 64bit mode which affects bitCount64/1->. For example try this in 32bit and 64bit modes:

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constants     m1 : unsigned64 = 0x5555555555555555.     m2 : unsigned64 = 0x3333333333333333.     m4 : unsigned64 = 0x0F0F0F0F0F0F0F0F.   %--- class predicates     bitCount64 : (unsigned64 Value) -> unsigned64 Count. clauses     bitCount64(Value) = Counter5 ** 0x7F :-         Counter0 = Value - (Value >> 1 ** m1),         Counter1 = (Counter0 ** m2) + (Counter0 >> 2 ** m2),         Counter2 = Counter1 + (Counter1 >> 4) ** m4,         Counter3 = Counter2 + (Counter2 >> 8),         Counter4 = Counter3 + (Counter3 >> 16),         Counter5 = Counter4 + (Counter4 >> 32).   class predicates     trailingZeroBits64 : (unsigned64 Value) -> unsigned64 Count. clauses     trailingZeroBits64(Value) = if Value = 0 then sizeBitsOf(unsigned64) else bitCount64(Value - 1 ** ~~Value) end if.   %--- class predicates     bitCount64_old : (unsigned64 Value) -> unsigned64 NumberOfOneBits. clauses     bitCount64_old(Value) = bit::bitAnd(Counter5, 0x7F) :-         Counter0 = Value - bit::bitAnd(bit::bitRight(Value, 1), m1),         Counter1 = bit::bitAnd(Counter0, m2) + bit::bitAnd(bit::bitRight(Counter0, 2), m2),         Counter2 = bit::bitAnd(Counter1 + bit::bitRight(Counter1, 4), m4),         Counter3 = Counter2 + bit::bitRight(Counter2, 8),         Counter4 = Counter3 + bit::bitRight(Counter3, 16),         Counter5 = Counter4 + bit::bitRight(Counter4, 32).   class predicates     trailingZeroBits64_old : (unsigned64 Value) -> unsigned64 NumberOfTrailingZeroBits. clauses     trailingZeroBits64_old(Value) =         if Value = 0 then sizeBitsOf(unsigned64) else bitCount64_old(bit::bitAnd(Value - 1, bit::bitNot(Value))) end if.   %--- clauses     run() :-         One = hasDomain(unsigned64, 1),         ShiftLeft = hasDomain(unsigned64, 3),         Value = bit::bitLeft(One, ShiftLeft),         stdIO::writeF('new: 0x%X -> %d\n', Value, trailingZeroBits64(Value)),         stdIO::writeF('old: 0x%X -> %d\n', Value, trailingZeroBits64_old(Value)).
Regards Martin

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Thomas Linder Puls
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Re: Wishlist Item

Unread post by Thomas Linder Puls » 26 May 2020 15:53

It is not a problem to add such a predicate. But I wonder whether the result should be an unsigned64 or an unsigned (clearly the number is at most 64, so it will easily fit into an unsigned)?
Regards Thomas Linder Puls
PDC

Martin Meyer
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Posts: 280
Joined: 14 Nov 2002 0:01

Re: Wishlist Item

Unread post by Martin Meyer » 26 May 2020 21:39

In my class bitAddOn I give all bit counts type positive or in some cases positiveOptional. For example I have

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predicates     getLowBitPos64 : (unsigned64 X) -> positiveOptional BitPosition.     % @short Returns the position of the lowest 1-bit     % @end
where a result of -1 means that there is no 1-bit in X, i.e. X is zero.
Regards Martin

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Thomas Linder Puls
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Re: Wishlist Item

Unread post by Thomas Linder Puls » 2 Jun 2020 8:28

Visual Prolog 9 build 906: trailingZeroBits64 has been added to bit, and bit counts has been changes to positive

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predicates     bitCount : (unsigned Value) -> positive Count.     bitCount64 : (unsigned64 Value) -> positive Count.     % @short Returns the number of non-zero bits     % @end   predicates     isPow2 : (unsigned Value) determ.     % @short Successful if only one bit is set to 1     % @end   predicates     trailingZeroBits : (unsigned Value) -> positive Count.     trailingZeroBits64 : (unsigned64 Value) -> positive Count.     % @short Calculating the number of consecutive low-order zeros     % @end
Regards Thomas Linder Puls
PDC

choibakk
Posts: 19
Joined: 5 Sep 2019 19:30

Re: Wishlist Item

Unread post by choibakk » 19 Jun 2020 23:14

Wow, thank you!

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