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| From | Ben <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.theory, comp.lang.c++ |
| Subject | Re: Implementing a two-way Turing Machine tape as an improvement to std::deque |
| Date | 2022-05-13 01:06 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <87wneq1ejm.fsf@bsb.me.uk> (permalink) |
| References | <cNWdnXqV1cXzEuD_nZ2dnUU7_8zNnZ2d@giganews.com> |
Cross-posted to 2 groups.
olcott <NoOne@NoWhere.com> writes:
I've removed the philosophy group and comp.lang.c as this is C++.
> C/C++ people please critique this as the basis for an improvement to
> std::deque.
You will get critiques of the code on whatever basis people feel
inclined to comment! You can't limit the comments to some particular
context.
> It seems to have the key functionality of std::deque and
> does it much more simply while saving time and space.
It does not have any of the functionality of std::deque. There is a
commonly used (though not particularly efficient) way to implement a
deque using two arrays, but this is not it.
> #define tape_element unsigned char
Use a typedef or using declaration. Also, I'd put the typedef in the
class as the type belongs to the class (as least that appears to be the
case from the name you've chosen).
> class Tape_Type
> {
> private:
> int Tape_Head = 0; // Can be negative
> std::vector<tape_element> Left; // Stores left expansion
> std::vector<tape_element> Right; // Stores right expansion
> tape_element & operator[](int index);
>
> public:
> void move_left(); // Tape_Head--; Left.push_back(0); as needed
> void move_right(); // Tape_Head++; Left.push_back(0); as needed
The comments are wrong since you push_back('_').
> void Write(tape_element Y){ this->operator[](Tape_Head) = Y; };
> tape_element Read() { return this->operator[](Tape_Head); };
I'd write (*this)[Tape_Head] but I suppose that's just a matter of style.
> Tape_Type(){ Right.push_back('_'); } // constructor
The constructor leaves a Tape_Type object in an unusable state, but
that's due to a bug in operator[]. Did you test?
> void Output();
> };
>
> tape_element& Tape_Type::operator[](int index)
> {
> if (index > 0)
> return Right[index];
Bug. You meant index >= 0 I think.
> int Left_Index = ((index * -1) -1);
Why not -index - 1?
> return Left[Left_Index];
Do you think introducing a new variable really make the code clearer
that simply writing
return Left[-index - 1];
? Personally, I'd write the whole thing as
return index >= 0 ? Right[index] : Left[-index - 1];
> }
>
> void Tape_Type::Output()
> {
> printf("Tape_Type::Output()\n");
>
> if (Left.size())
> {
> int Last_One = Left.size() - 1;
> for (int N = Last_One; N >= 0; N--)
> {
> int TH = (N + 1) * -1; // determine Tape_Head from N
> printf("[%04d]:%c Left[%02d]\n", TH, Left[N], N);
> }
> }
> if (Right.size())
> for (int N = 0; N < Right.size(); N++)
> printf("[%04d]:%c Right[%02d]\n", N, Right[N], N);
> }
>
> void Tape_Type::move_left()
> {
> Tape_Head--;
> int Left_Index = ((Tape_Head * -1) -1);
> if (Left_Index == Left.size())
> Left.push_back('_');
> }
>
> void Tape_Type::move_right()
> {
> Tape_Head++;
> if (Tape_Head == Right.size())
> Right.push_back('_');
> }
I find the capitalisation odd and unhelpful as there does not seem to be
any consistency about it.
--
Ben.
"le génie humain a des limites, quand la bêtise humaine n’en a pas"
Alexandre Dumas (fils)
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Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 17:51 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-12 23:56 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 18:09 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 00:22 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 18:38 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 00:40 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 18:49 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 00:53 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 19:12 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 01:58 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 20:34 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 08:02 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque tth <tth@none.invalid> - 2022-05-13 09:10 +0200
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-13 10:58 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 17:02 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com> - 2022-05-13 12:44 -0700
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Richard Damon <Richard@Damon-Family.org> - 2022-05-12 19:23 -0400
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 18:32 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Ben <ben.usenet@bsb.me.uk> - 2022-05-13 01:06 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 19:55 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 02:01 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 20:36 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 08:04 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-13 11:00 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Mr Flibble <flibble@reddwarf.jmc> - 2022-05-13 17:04 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-13 12:05 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Ben <ben.usenet@bsb.me.uk> - 2022-05-13 02:38 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-12 21:37 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Python <python@example.invalid> - 2022-05-13 04:39 +0200
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Ben <ben.usenet@bsb.me.uk> - 2022-05-13 12:01 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-13 10:41 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Richard Damon <Richard@Damon-Family.org> - 2022-05-13 11:56 -0400
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Ben <ben.usenet@bsb.me.uk> - 2022-05-13 17:35 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-13 12:12 -0500
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque Ben <ben.usenet@bsb.me.uk> - 2022-05-13 20:04 +0100
Re: Implementing a two-way Turing Machine tape as an improvement to std::deque olcott <NoOne@NoWhere.com> - 2022-05-13 14:19 -0500
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