1_histogram

Round 1: Byte-pair histogram

Problem

Given a binary payload of up to a few hundred megabytes, count the frequency of every 2-byte bigram. The output is a mapping from each observed bigram to its occurrence count.

A bigram is a sliding window of two adjacent bytes. For the payload b"ABCD" the bigrams are b"AB", b"BC", and b"CD". An N-byte payload therefore contains N - 1 bigrams. With 256 possible byte values each, the full universe is 256 * 256 = 65,536 distinct tokens.

• Input: data/payload.bin (default 10 MB, biased byte distribution).
• Output: a dict (or equivalent) keyed by 2-byte token, mapped to an int count.
• Universe: up to 65,536 distinct bigrams.

Files

File	Purpose
baseline.py	Intentionally slow starting point. Don't edit: it is the reference for the comparison.
solution.py	Edit this. Starts out delegating to baseline.py; replace with your faster implementation.
gen_data.py	Generates data/payload.bin and data/fixture/payload.bin.
test_histogram.py	Correctness tests and the pytest-codspeed benchmark. Every test is parametrized over both the baseline and your solution.

Generate the data

uv run rounds/1_histogram/gen_data.py            # default 10 MB.
uv run rounds/1_histogram/gen_data.py --size-mb 50

Or run uv run scripts/setup.py to generate every round's data in one go.

Verify correctness

uv run pytest rounds/1_histogram/

Benchmark

Walltime, locally:

uv run pytest --codspeed rounds/1_histogram/

Same benchmarks, run through the CodSpeed CLI for low-noise instrumented measurements:

codspeed run --mode walltime -- uv run pytest --codspeed rounds/1_histogram/