* rand() use XOR to break up unwanted pair correlation
This form of rand() cannot return the same value twice in a row.
Two additonal EOR instructions produce a more even distribution of successive pairs.
see comments on #951
* rand.s document purpose of XOR
* suggested srand() optimization: zero fill unnecessary
* test to validate implementation of rand()
* srand() improving behaviour and adding startup test
* srand() with a tail call to rand() for better initial shuffle
* srand() can fall through to rand() instead of tail call
For some reason or another both the author of the PR in question and its reviewers didn't notice that the two functions in question were totally overlooked.
3d8c3a4948 caused an unintended "shadowing" of files in /libsrc/runtime by files in /libsrc/common. Therefore the files in question are renamed (again) in /libsrc/common to make the files in /libsrc/runtime "visible" again.
We want to add the capability to not only get the time but also set the time, but there's no "setter" for the "getter" time().
The first ones that come into mind are gettimeofday() and settimeofday(). However, they take a struct timezone argument that doesn't make sense - even the man pages says "The use of the timezone structure is obsolete; the tz argument should normally be specified as NULL." And POSIX says "Applications should use the clock_gettime() function instead of the obsolescent gettimeofday() function."
The ...timeofday() functions work with microseconds while the clock_...time() functions work with nanoseconds. Given that we expect our targets to support only 1/10 of seconds the microseconds look preferable at first sight. However, already microseconds require the cc65 data type 'long' so it's not such a relevant difference to nanoseconds. Additionally clock_getres() seems useful.
In order to avoid code duplication clock_gettime() takes over the role of the actual time getter from _systime(). So time() now calls clock_gettime() instead of _systime().
For some reason beyond my understanding _systime() was mentioned in time.h. _systime() worked exactly like e.g. _sysremove() and those _sys...() functions are all considered internal. The only reason I could see would be a performance gain of bypassing the time() wrapper. However, all known _systime() implementations internally called mktime(). And mktime() is implemented in C using an iterative algorithm so I really can't see what would be left to gain here. From that perspective I decided to just remove _systime().
So far time_t values were interpreted as local time values. However, usually time_t values are to be interpreted as "seconds since 1 Jan 1970 in UTC". Therefore all logic handling time_t values has to be changed.
- So far gmtime() called localtime() with an adjusted time_t, now localtime() calls gmtime() with an adjusted time_t.
- mktime() has to do "the opposite" of localtime(), to keep it that way mktime() does now the inverse adjustment made by localtime().
- All currently present time() implementations internally call mktime() so they don't require individual adjustments.
