> That's going to be a pointer, where a value that causes the CPU to trap is quite handy.
You're confusing an invalid pointer with an invalid index. There is absolutely no reason for any index to ever be invalid.
> And there's already plenty of invalid index values. -1 for example.
-1 is not representable with unsigned integers. There are no invalid index values in a 0-based indexing system (using unsigned integers, as I initially stated).
> There's no way to make an allocation the size of your entire ram, so 0xff...f is going to be invalid.
This is so completely off the mark I'm surprised you even came up with it. There are several things wrong with this (off the top of my head):
1. I don't need an allocation the size of my address space in order to want to address both the first and last bytes in the address space.
2. You don't know what machine I'm running on. This could be an embedded 16-bit machine without multiprocessing with 64KB of RAM. Every single addressable byte is valid and corresponds to RAM storage.
3. It doesn't even matter whether or not a given address can be loaded. Indexing a pointer does not necessarily require loading it. As a trivial example, I could take the address of the resulting indexed value.
>You're confusing an invalid pointer with an invalid index. There is absolutely no reason for any index to ever be invalid.
I'm not confusing them. You are very clearly describing a pointer.
>-1 is not representable with unsigned integers.
When I wrote -1 I meant "the value you get when you type -1 in your source code".
>This is so completely off the mark I'm surprised you even came up with it. There are several things wrong with this (off the top of my head):
>1. I don't need an allocation the size of my address space in order to want to address both the first and last bytes in the address space.
That's a pointer issue. If I allocate 20 bytes near the end of ram, my last index is only going to be 19 or 20, so it doesn't matter if I can't go to UINT_MAX.
> 2. You don't know what machine I'm running on. This could be an embedded 16-bit machine without multiprocessing with 64KB of RAM. Every single addressable byte is valid and corresponds to RAM storage.
Again, that's a pointer.
> 3. It doesn't even matter whether or not a given address can be loaded. Indexing a pointer does not necessarily require loading it. As a trivial example, I could take the address of the resulting indexed value.
You're confusing an invalid pointer with an invalid index. There is absolutely no reason for any index to ever be invalid.
> And there's already plenty of invalid index values. -1 for example.
-1 is not representable with unsigned integers. There are no invalid index values in a 0-based indexing system (using unsigned integers, as I initially stated).
> There's no way to make an allocation the size of your entire ram, so 0xff...f is going to be invalid.
This is so completely off the mark I'm surprised you even came up with it. There are several things wrong with this (off the top of my head):
1. I don't need an allocation the size of my address space in order to want to address both the first and last bytes in the address space.
2. You don't know what machine I'm running on. This could be an embedded 16-bit machine without multiprocessing with 64KB of RAM. Every single addressable byte is valid and corresponds to RAM storage.
3. It doesn't even matter whether or not a given address can be loaded. Indexing a pointer does not necessarily require loading it. As a trivial example, I could take the address of the resulting indexed value.