cut: make memory allocation independent of range width
The current implementation of cut, uses a bit array,
an array of `struct range_pair's, and (when --output-delimiter
is specified) a hash_table. The new implementation will use
only an array of `struct range_pair's.
The old implementation is memory inefficient because:
1. When -b with a big num is specified, it allocates a lot of
memory for `printable_field'.
2. When --output-delimiter is specified, it will allocate 31 buckets.
Even if only a few ranges are specified.
Note CPU overhead is increased to determine if an item is to be printed,
as shown by:
$ yes abcdfeg | head -n1MB > big-file
$ for c in with-bitarray without-bitarray; do
src/cut-$c 2>/dev/null
echo -ne "\n== $c =="
time src/cut-$c -b1,3 big-file > /dev/null
done
== with-bitarray ==
real 0m0.084s
user 0m0.078s
sys 0m0.006s
== without-bitarray ==
real 0m0.111s
user 0m0.108s
sys 0m0.002s
Subsequent patches will reduce this overhead.
* src/cut.c (set_fields): Set and initialize RP
instead of printable_field.
* src/cut.c (is_range_start_index): Use CURRENT_RP rather than a hash.
* tests/misc/cut.pl: Check if `eol_range_start' is set correctly.
* tests/misc/cut-huge-range.sh: Rename from cut-huge-to-eol-range.sh,
and add a test to verify large amounts of mem aren't allocated.
Fixes http://bugs.gnu.org/13127