On Wed, Dec 7, 2022 at 4:22 PM Ian Lance Taylor <iant@golang.org> wrote:
>
> This patch adds zstd support to libbacktrace, to support the new
> linker option --compress-debug-sections=zstd.

This patch rewrites and simplifies the main zstd decompression loop
using some ideas from the reference implementation.  This speeds it up
a bit, although it still runs at about 35% of the speed of the
reference implementaiton.  Bootstrapped and ran libbacktrace tests on
x86_64-pc-linux-gnu.  Committed to mainline.

Ian

* elf.c (ZSTD_TABLE_*): Use elf_zstd_fse_baseline_entry.
(ZSTD_ENCODE_BASELINE_BITS): Define.
(ZSTD_DECODE_BASELINE, ZSTD_DECODE_BASEBITS): Define.
(elf_zstd_literal_length_base): New static const array.
(elf_zstd_match_length_base): Likewise.
(struct elf_zstd_fse_baseline_entry): Define.
(elf_zstd_make_literal_baseline_fse): New static function.
(elf_zstd_make_offset_baseline_fse): Likewise.
(elf_zstd_make_match_baseline_fse): Likewise.
(print_table, main): Use elf_zstd_fse_baseline_entry.
(elf_zstd_lit_table, elf_zstd_match_table): Likewise.
(elf_zstd_offset_table): Likewise.
(struct elf_zstd_seq_decode): Likewise.  Remove use_rle and rle
fields.
(elf_zstd_unpack_seq_decode): Use elf_zstd_fse_baseline_entry,
taking a conversion function.  Convert RLE to FSE.
(elf_zstd_literal_length_baseline): Remove.
(elf_zstd_literal_length_bits): Remove.
(elf_zstd_match_length_baseline): Remove.
(elf_zstd_match_length_bits): Remove.
(elf_zstd_decompress): Use elf_zstd_fse_baseline_entry.  Rewrite
and simplify main loop.