improved last

[Denys Vlasenko]

On Wednesday 21 May 2008 19:44, Denys Vlasenko wrote:
> > > Can you work on it a bit more?
> > >
> > > static int boot_down = 0;
> > >
> > > Completely wasted four bytes. grep for it.
> > 
> > Alright, I did that and managed to save 2 bytes.  I also tested to
> > remove most of the other static variables.  That led to increased
> > size.  If you think the 2 bytes lighter version of the applet is
> > interesting, just let me know.
> 
> This is a 10-minute worth of shrinking:
> 
> function                                             old     new   delta
> show_entry                                           355     359      +4
> boot_down                                              4       1      -3
> show_wide                                              4       -      -4
> filename                                               4       -      -4
> last_main                                           1084    1030     -54
> ------------------------------------------------------------------------------
> (add/remove: 0/2 grow/shrink: 1/2 up/down: 4/-65)             Total: -61 bytes
> 
> # size last-org.o last.o
>    text    data     bss     dec     hex filename
>    1730      12      24    1766     6e6 last-org.o
>    1680       8      17    1705     6a9 last.o

And this one is even smaller:

# ./.cmklog bloatcheck
function                                             old     new   delta
show_entry                                           355     359      +4
start_time                                             4       -      -4
show_wide                                              4       -      -4
list                                                 388     384      -4
filename                                               4       -      -4
boot_down                                              4       -      -4
static.ret                                             8       -      -8
static.pos                                             8       -      -8
last_main                                           1084    1058     -26
add_entry                                             45       -     -45
------------------------------------------------------------------------------
(add/remove: 0/7 grow/shrink: 1/2 up/down: 4/-107)           Total: -103 bytes

In particular, it doesn't have any data/bss:

# size last-org.o last.o
   text    data     bss     dec     hex filename
   1730      12      24    1766     6e6 last-org.o
   1663       0       0    1663     67f last.o

One bug fixed. Old code was:

        lseek(file, -(off_t)sizeof(struct utmp), SEEK_END);

        for (;;) {
                if (read_entry(file, &ut) != sizeof(struct utmp)) {
                        break;
                }

static int read_entry(int file, struct utmp *ut)
{
...
        n = full_read(file, ut, sizeof(struct utmp));

Imagine what will happen if the file is empty...

I changed the logic so that it handles that case.
However, if the file's size is not a multiple of sizeof(struct utmp),
both old and current code will be totally confused.

Unknown number of bugs added...
--
vda
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