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What of having a pure ANSI C implementation of pack and unpack available? I, too, am concerned with future data loss due to codec extinction. A solution seems

What of having a pure ANSI C implementation of pack and unpack available? I, too, am concerned with future data loss due to codec extinction. A solution seems like it’d take the shape of an archive of the codecs in a simple, pure C subset with an actively maintained compiler. Unused code should be refactored out of mainstream tools

lmm 9y ago
There's no test suite for "pure ANSI C". Even experts tend to write code that relies on undefined behaviour. I'd sooner trust e.g. Java bytecode to remain executable in the future.
- microcolonel 9y ago
  The C compatibility test comes when you build your kernel, your toolchain, your browsers, your shells, your desktop applications, and run their test suites after each build. ;- ) "ANSI C" is a bit of a misnomer, since a) there have been updates to the ANSI standard which are not considered "ANSI C", and b) all of the updates are sworn to be backward compatible.
  - lmm 9y ago
    > The C compatibility test comes when you build your kernel, your toolchain, your browsers, your shells, your desktop applications, and run their test suites after each build. ;- ) But if we're talking about obscure applications being preserved for posterity, they're not going to get built. Really I was talking about the other direction though: a way to confirm that a given program is written using only ANSI C. There's no testsuite for that, all you can do is test with the compilers that exist - and then sometimes your program suddenly stops working in the next version of the compiler.
    - microcolonel 9y ago
      > But if we're talking about obscure applications being preserved for posterity, they're not going to get built. Well, they don't really need to be, that's the point. > Really I was talking about the other direction though: a way to confirm that a given program is written using only ANSI C. There's no testsuite for that, all you can do is test with the compilers that exist - and then sometimes your program suddenly stops working in the next version of the compiler. See --std=c89 or -ansi flags on GCC or Clang. One other way to prevent other sources of rot is to avoid UB that is frequently subject to change. Most UB is defined, at worst, by the constraints of real ISAs (i.e. the behaviour of idiv when dividing INT_MIN by -1 is an exception on x86, but the ARMv7 equivalent simply produces a number), and most UB-altering characteristics are standard across popular ISAs, and new (general purpose) ISAs tend to go with the status quo when in doubt. And if all else fails, you can still run your code in an ISA simulator, and compile it with an old compiler, to figure out exactly what it meant in the past.
      - lmm 9y ago
        > See --std=c89 or -ansi flags on GCC or Clang. They won't help you if your code relies on behaviour not defined in the standard, which is almost always what happens in practice. > Most UB is defined, at worst, by the constraints of real ISAs (i.e. the behaviour of idiv when dividing INT_MIN by -1 is an exception on x86, but the ARMv7 equivalent simply produces a number), and most UB-altering characteristics are standard across popular ISAs, and new (general purpose) ISAs tend to go with the status quo when in doubt. ISA extensions aren't always so conservative - x86 family ISAs used to never have alignment requirements, but some of the newer SSE-family instructions do. And modern C compilers will optimise code that invokes UB in surprising ways - codepaths that do signed integer overflow on x86 used to silently wrap around in twos-complement fashion, long shifts used to behave the way the hardware did, but these days compilers will omit to generate code for that codepath since the behaviour is officially undefined. > And if all else fails, you can still run your code in an ISA simulator, and compile it with an old compiler, to figure out exactly what it meant in the past. Sure, but in that case you're not gaining anything from using ANSI C, and might as well stick with whatever the code is written in, or just keep the binaries and run them on an emulator.
    - comex 9y ago
      You might be interested in tis-interpreter: http://trust-in-soft.com/tis-interpreter/ http://trust-in-soft.com/tis-interpreter/ It can’t prove a program is 100% conformant, but it can detect a much broader range of undefined behaviors than regular compilers, and does other things more strictly (like, IIRC, limiting the declarations exposed by standard library includes to what the standards guarantees they expose).
- TheCondor 9y ago
  What if it were pure “archival C” whereby the project maintainers defined the undefined behaviors? And I don’t think it would need SIMD optimizations and such, it’s not designed for performance so much as to keep code runnable. It’d probably require some sort of VM specification too, maybe java is a better choice. keeping the code “alive” by keeping it in a project when it’s never used doesn’t seem like a strong guarantee that it will still work when you need it.

lmm 9y ago

There's no test suite for "pure ANSI C". Even experts tend to write code that relies on undefined behaviour. I'd sooner trust e.g. Java bytecode to remain executable in the future.

microcolonel 9y ago
The C compatibility test comes when you build your kernel, your toolchain, your browsers, your shells, your desktop applications, and run their test suites after each build. ;- ) "ANSI C" is a bit of a misnomer, since a) there have been updates to the ANSI standard which are not considered "ANSI C", and b) all of the updates are sworn to be backward compatible.
- lmm 9y ago
  > The C compatibility test comes when you build your kernel, your toolchain, your browsers, your shells, your desktop applications, and run their test suites after each build. ;- ) But if we're talking about obscure applications being preserved for posterity, they're not going to get built. Really I was talking about the other direction though: a way to confirm that a given program is written using only ANSI C. There's no testsuite for that, all you can do is test with the compilers that exist - and then sometimes your program suddenly stops working in the next version of the compiler.
  - microcolonel 9y ago
    > But if we're talking about obscure applications being preserved for posterity, they're not going to get built. Well, they don't really need to be, that's the point. > Really I was talking about the other direction though: a way to confirm that a given program is written using only ANSI C. There's no testsuite for that, all you can do is test with the compilers that exist - and then sometimes your program suddenly stops working in the next version of the compiler. See --std=c89 or -ansi flags on GCC or Clang. One other way to prevent other sources of rot is to avoid UB that is frequently subject to change. Most UB is defined, at worst, by the constraints of real ISAs (i.e. the behaviour of idiv when dividing INT_MIN by -1 is an exception on x86, but the ARMv7 equivalent simply produces a number), and most UB-altering characteristics are standard across popular ISAs, and new (general purpose) ISAs tend to go with the status quo when in doubt. And if all else fails, you can still run your code in an ISA simulator, and compile it with an old compiler, to figure out exactly what it meant in the past.
    - lmm 9y ago
      > See --std=c89 or -ansi flags on GCC or Clang. They won't help you if your code relies on behaviour not defined in the standard, which is almost always what happens in practice. > Most UB is defined, at worst, by the constraints of real ISAs (i.e. the behaviour of idiv when dividing INT_MIN by -1 is an exception on x86, but the ARMv7 equivalent simply produces a number), and most UB-altering characteristics are standard across popular ISAs, and new (general purpose) ISAs tend to go with the status quo when in doubt. ISA extensions aren't always so conservative - x86 family ISAs used to never have alignment requirements, but some of the newer SSE-family instructions do. And modern C compilers will optimise code that invokes UB in surprising ways - codepaths that do signed integer overflow on x86 used to silently wrap around in twos-complement fashion, long shifts used to behave the way the hardware did, but these days compilers will omit to generate code for that codepath since the behaviour is officially undefined. > And if all else fails, you can still run your code in an ISA simulator, and compile it with an old compiler, to figure out exactly what it meant in the past. Sure, but in that case you're not gaining anything from using ANSI C, and might as well stick with whatever the code is written in, or just keep the binaries and run them on an emulator.
  - comex 9y ago
    You might be interested in tis-interpreter: http://trust-in-soft.com/tis-interpreter/ http://trust-in-soft.com/tis-interpreter/ It can’t prove a program is 100% conformant, but it can detect a much broader range of undefined behaviors than regular compilers, and does other things more strictly (like, IIRC, limiting the declarations exposed by standard library includes to what the standards guarantees they expose).
TheCondor 9y ago
What if it were pure “archival C” whereby the project maintainers defined the undefined behaviors? And I don’t think it would need SIMD optimizations and such, it’s not designed for performance so much as to keep code runnable. It’d probably require some sort of VM specification too, maybe java is a better choice. keeping the code “alive” by keeping it in a project when it’s never used doesn’t seem like a strong guarantee that it will still work when you need it.