cmp: stop skipping bytes if EOF is reached

Currently, if a skip value is larger than the file size, cmp will continue
to loop and call getc() until the skip count is satisfied, even though
EOF has been reached.

For large skip values (e.g., 1 billion), this results in significant
CPU waste and execution time (e.g., 11 seconds on a modern CPU).

This patch checks for EOF inside the skip loop and breaks early.

Test case:
$ touch empty.txt
$ time ./busybox cmp empty.txt empty.txt 1000000000 1000000000

Before:
real    0m10.937s

After:
real    0m0.002s

function                                             old     new   delta
cmp_main                                             594     616     +22

Signed-off-by: Giorgi Tchankvetadze <giorgitchankvetadze1997@gmail.com>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

0 files changed, 0 insertions, 0 deletions