[TUHS] Unix stories

Steffen Nurpmeso steffen at sdaoden.eu
Thu Feb 9 23:46:28 AEST 2017


Hello,

Random832 <random832 at fastmail.com> wrote:
 |On Wed, Jan 4, 2017, at 11:22, Steffen Nurpmeso wrote:
 |> Random832 <random832 at fastmail.com> wrote:
 |>|On Wed, Jan 4, 2017, at 08:04, Steffen Nurpmeso wrote:
 |>|> terrible aliasing and "sequence point" rules, where i think it is
 |>|> clear what i mean when i write "i = j + ++i" (i believe this is
 |>|> undefined behaviour).
 |>|
 |>|I assume you're imagining it as being equivalent to i = j + i + 1, with
 |>|a redundant store operation.
 |>|
 |>|But why couldn't it equally well mean
 |> 
 |> No i don't,
 |
 |Then I guessed wrong. Again. (So much for "clear", I suppose). But
 |you're the one who "think[s] it's clear what [you] mean by it"; so you
 |simply *must* have a meaning in mind. Why not explain what it is?

so now i really got this a few minute ago after adding negative
history number support (to count from history top):

  tty.c: In function 'c_history':
  tty.c:4157:13: warning: operation on 'entry' may be undefined [-Wsequence-point]
         entry = isneg ? --entry : (siz_t)a_tty.tg_hist_size - entry;
         ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

And in my opinion this is just plain terrible?  I think it is
absolutely clear what i intend, there is not even a dereferenced
pointer involved, the lhv is either a register or if all fails
a stack location.  I don't understand why i have to write

      if(isneg)
         --entry;
      else
         entry = (siz_t)a_tty.tg_hist_size - entry;

to get over this, it is exactly the same?  And it is not that easy
as blaming the compiler (except that gcc often comes over with
terrible warnings, but this is a different issue, and of course,
these are huge codebases and i guess you stumble along and fix the
test warnings that occur when a step turned on some red lights
somewhere else; ok, but while i am in rant mode, i recently had to
introduce a useless enum to turn

 #ifdef HAVE_DEVEL /* Avoid gcc warn cascade since n_ignore is defined locally */
 -n_CTAV(-(uintptr_t)n_IGNORE_TYPE - n__IGNORE_ADJUST == 0);

into

  +n_CTAV(-n__IGNORE_TYPE - n__IGNORE_ADJUST == 0);

where n_IGNORE_TYPE was '#define n_IGNORE_TYPE ((struct
n_ignore*)-3)', and if that is not an integer then, what).  
No, in my opinion this is because of overly construed standard
text of an increasingly unclean standard.  Digging in the dirt is
my whole life anyway, even i don't read newspapers, and i really
would like to see C not becoming just an equal soup of muddy
waters.  Just my one cent.

--steffen


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