Before this change, we would first find all changes so we could obtain
the largest offset we will report and use that to set up the padding.
Now we use the file sizes to estimate the largest possible offset.
Not only does this allow us to print earlier, reduces memory usage, as
we do not store diffs to report later, but it also fixes a case in
which our output was different to GNU cmp's - because it also seems
to estimate based on size.
Memory usage drops by a factor of 1000(!), without losing performance
while comparing 2 binaries of hundreds of MBs:
Before:
Maximum resident set size (kbytes): 2489260
Benchmark 1: ../target/release/diffutils \
cmp -l -b /usr/lib64/chromium-browser/chromium-browser /usr/lib64/firefox/libxul.so
Time (mean ± σ): 14.466 s ± 0.166 s [User: 12.367 s, System: 2.012 s]
Range (min … max): 14.350 s … 14.914 s 10 runs
After:
Maximum resident set size (kbytes): 2636
Benchmark 1: ../target/release/diffutils \
cmp -l -b /usr/lib64/chromium-browser/chromium-browser /usr/lib64/firefox/libxul.so
Time (mean ± σ): 13.724 s ± 0.038 s [User: 12.263 s, System: 1.372 s]
Range (min … max): 13.667 s … 13.793 s 10 runs
Olivier Tilloy
renovate[bot]
Daniel Hofstetter
Sylvestre Ledru
Gustavo Noronha Silva