mirror of
https://github.com/libretro/RetroArch.git
synced 2026-11-07 08:36:02 -10:00
LibretroAdmin
cdf84534e2
A memory search visited every item of the core's memory in turn: a
region lookup, a branch on item size, a loop over sub-items that at
byte size and wider runs once, and a branch on the search type, even
for items an earlier search had already ruled out - after a search or
two, nearly all of them. Each failing item also cost a memset call,
and the match count was reloaded and stored every item, since stores
through the uint8_t match bytes may alias it.
Now:
- Regions are walked in order, items at multiples of their size lying
whole inside one, as before, without a lookup per item.
- Runs of clear match bytes are stepped over 16 bytes at a time with
SSE2, 32 with AVX2 or 64 with AVX-512BW (chosen at run time from
cpu_features_get(); built per function, and under PlayStation clang
or clang-cl only where the baseline enables them), or a word at a
time elsewhere. An item is still judged by its first match byte: a
set byte part-way through one, which a change of item size between
searches can leave, rounds back to the item's start.
- At byte, 16- and 32-bit sizes the search type is chosen once and
each type gets its own loop, with direct stores for a failing item
and the count held in a local. The 1-, 2- and 4-bit sizes keep the
general path.
32-bit values were assembled as byte * 256 * 256 * 256 in int, which
overflows (undefined) for a top byte of 0x80 or more; they use
unsigned shifts now, the same value.
33 MB of memory on an AVX-512 Xeon, before -> after:
8-bit items: first search 270-344 -> 45-48 ms,
after one search 146-188 -> 91-126 ms,
after two 128-162 -> 9-12 ms
32-bit items: first search 75-125 -> 18-80 ms,
later searches 49-66 -> 5-11 ms
samples/cheats/cheat_search keeps the previous algorithm as its
reference and checks the match bytes, the match count and the saved
memory after each of 14400 chained searches: random region layouts,
every item size, both byte orders, every search type, memory changed
between searches in runs or scattered, the item size changed without
starting over, and the scan capped at each SIMD tier in turn.
samples/cheats/cheat_regions reports no SIMD, so it runs the baseline
scan.