It's a 32-bit-access-only heap. On the Ultimate Doom WAD the amount of
data moved is about 17 kiB, which is not a lot, but arrays with 4-byte
elements are not easy to find in Doom.
This was using screens[1] which I had deallocated when fixing the status
bar (I incorrectly assumed it was used only for that).
While the CGDOOM technique to share screens[1] to avoid allocating the
320x20 buffer for the status bar makes clear sense with that new
information, I think I'll keep this 6.4 kB buffer there and rather
search for ways to use more memory zones.
Loading is measured by RTC_GetTicks().
* Initial version: 9.8s
This was a regression due to using 512-byte sectors instead of 4 kiB
clusters as previously.
* Do BFile reads of 4 kiB: 5.2s (-47%)
Feels similar to original code, I'll take this as my baseline.
* Test second half of Flash first: 3.6s (-31%)
By reading from FLASH_FS_HINT to FLASH_END first many OS sectors can
be skipped (without missing on other sectors just in case).
* Load to XRAM instead or RAM with BFile
The DMA is 10% slower to XRAM than to RAM, but this benefits memcmp()
because of faster memory accesses through the operand bus. No effect
at this point, but ends up saving 8% after memcmp is optimized.
* Optimize memcmp for sectors: 3376 ms (-8%)
The optimized memcmp uses word accesses for ROM (which is fastest),
and weaves loop iterations to exploit superscalar parallelism.
* Search sectors most likely to contain data first: 2744 ms (-19%)
File fragments almost always start on 4-kiB boundaries between
FLASH_FS_HINT and FLASH_END, so these are tested first.
* Index most likely sectors, improve FLASH_FS_HINT: 2096 ms (-24%)
Most likely sectors are indexed by first 4 bytes and binary searched,
and a slightly larger region is considered for hints. The cache hits
119/129 fragments in my case.
* Use optimized memcmp for consecutive fragments: 1408 ms (-33%)
I only set it for the search of the first sector in each fragment and
forgot to use it where it is really needed. x)
Game speed is measured roughly by the time it takes to hit a wall by
walking straight after spawning in Hangar.
* Initial value: 4.4s
* Use cached ROM when loading data from the WAD: 2.9s (-35%)
Cached accesses are quite detrimental for sector search, I assume
because everything is aligned like crazy, but it's still a major help
when reading sequential data in real-time.
* Restore screen numbers; BG is 4, at least in the ST module.
* Let ST module allocate BG, which is just 32 pixels high and not a full
VRAM (huge memory gain!)
* Fix V_CopyRect() not working because memcpy is still broken (this will
be changed later with a proper memcpy)
Lephenixnoir
ComputerNerd