libk  Check-in [9ea8c28897]

Modified libk.md from [abadd8c1b0] to [157104d9ca].

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   212    212   this makes code much more legible and has the added benefit of making the definitions easier to expand at a later date if new functionality is needed without breaking the API or ABI.
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   214    214   ## error handling
   215    215   every module has a `cond` type (e.g. `kscond` for `kstr` or `kconf_cond` for `kconf`). this is an enumeration type that represents every possible error a module can return, and every `cond` type obeys a number of invariants (in addition to the usual namespacing rules:
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   217    217   1. every member of a `cond` type has an integer value that is unique among all modules' `cond` types. for instance, this means that `kscond_ok` has an integer value that is not equal to `kmcond_ok`.
   218         -2. every member of a cond type has a member `kmcond_ok` which represents total success. this member's integer value is always an exact multiple of the "module offset", the number of condition values allocated to each module (currently `0x7F`).
          218  +2. every member of a cond type has a member `*cond_ok` which represents total success. this member's integer value is always an exact multiple of the "module offset", the number of condition values allocated to each module (currently `0x7F`).
   219    219   3. the `kokay()` function, defined in `kcore`, when called on a member of a `cond` type will return true if that member represents total success and false otherwise.
   220    220   4. every cond type has a value `*cond_fail`, for instance `kconf_cond_fail`. if a condition is greater than or equal to its module's `fail` value, it represents a total failure. if it is lesser than the fail value, it represents either success, partial success, or some other condition that does not equate to total failure.
   221    221   5. if a `cond` value is greater than its module's `*cond_ok` value but less than the `*cond_fail` value, it represents a condition that is neither total success nor total failure; for instance, a partial write, or an attempt to free memory that does not need to be freed.
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   223    223   the reason each error value is unique is that this allows us to map every single condition code unambiguously to an error message. a forthcoming `kcore` function will do exactly that and produce an error string that can be displayed to a user or for debugging purposes. another useful property is that each integer value has at most only one possible meaning in the context of error codes, allowing for centralized error handling - a `kscond` and a `kmcond` can both be turned into an `int` without loss of information, and e.g. `kscond_fail` != `kmcond_fail` != `kconf_cond_fail`.
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   225    225   this is particularly useful as C does not have exceptions, and thus the only viable error-handling mechanisms are early-exit and early-return; any `cond` value can be propagated up the function stack without losing its unique meaning.