Improves bsdiff performance by preventing excessive iterations when processing similar data blocks

[wfairclough]

We detected a performance issue in our CI where the BinaryDelta process was taking over 4 hours to generate deltas between our macOS binaries. After timing individual bsdiff operations, I identified that a single diff was causing most of the slowdown. The issue occurred in the main macOS binary (Contents/MacOS/<AppName>) diffing process after product changes that removed approximately 22MB of binary code. By implementing patches from the ChromiumOS project's version of bsdiff, we reduced the entire BinaryDelta process from hours to just 5 minutes.

The changes introduce a mechanism to detect when bsdiff gets stuck processing large blocks of data that differ by less than 8 bytes. After 100 iterations in such a state, the algorithm breaks out of the loop to prevent performance degradation. Additionally, the search comparison operator was updated to include equality cases.

Original ChromiumOS Changes:

426e4aa AU: bsdiff: Expand pathological case where files differ by <8 bytes by Thieu Le · 13 years ago
58146f7 AU: Fix bsdiff hang by Thieu Le · 13 years ago
a055996 bsdiff: Speed up pathological case. by Thieu Le · 14 years ago

a055996
bsdiff: Speed up pathological case.

bsdiff does not properly handle the case where there is a large block of
data in the new file that only differs from the old file by less than 8
bytes.  This causes bsdiff to continue searching through the files one
byte at a time and at each byte, re-compare the same large block of data
which leads to excessively long run times.  This fix checks for this
edge condition and breaks out of the search loop early.  This retains
the size efficiency of the patch file for most binaries while preserving
the runtime efficiency for files that fall into this category.

https://chromium.googlesource.com/chromiumos/third_party/bsdiff/+/a055996c743add7a9558839276fd1e4994d16bd3%5E%21/#F0

58146f7
AU: Fix bsdiff hang

https://chromium.googlesource.com/chromiumos/third_party/bsdiff/+/58146f74abd6b1b69693943195f37f4ac6a6acef%5E%21/#F0

426e4aa
AU: bsdiff: Expand pathological case where files differ by <8 bytes

Modify bsdiff to better handle the case where files differ by <8 bytes
in some regions, not limitting this case to linear traversal.

BUG=chromium-os:28552
TEST=Manual bsdiff of problematic files, update engine unit tests

https://chromium.googlesource.com/chromiumos/third_party/bsdiff/+/426e4aa1cbeb3c8a73002047d7a796ca8e5e17d4%5E%21/#F0

Misc Checklist

• My change requires a documentation update on Sparkle's website repository
• My change requires changes to generate_appcast, generate_keys, or sign_update

Testing

I tested and verified my change by using one or multiple of these methods:

• Sparkle Test App
• Unit Tests
• My own app
• Other (please specify)

macOS version tested: 15.3

[wfairclough]

• Improves bsdiff performance by preventing excessive iterations when processing similar data blocks #1 👈 (View in Graphite)
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[tristanlabelle]

Would upstream accept this PR so we don't have to fork?