Add direct snprintf vs ctprintf benchmark comparison page

.github/workflows/benchmark.yml

@@ -41,3 +41,19 @@ jobs:
                   gh-pages-branch: gh-pages
                   benchmark-data-dir-path: .
                   auto-push: true
+
+            - name: Render snprintf vs ctprintf comparison
+              run: |
+                  python3 scripts/benchmark-comparison.py \
+                      ctprintf/build/benchmark/benchmarks/benchmark_results.json \
+                      /tmp/comparison.html "$GITHUB_STEP_SUMMARY"
+
+            - name: Publish comparison page
+              run: |
+                  git fetch origin gh-pages
+                  git checkout -f gh-pages
+                  cp /tmp/comparison.html comparison.html
+                  git add comparison.html
+                  git -c user.name=github-actions -c user.email=github-actions@github.com \
+                      commit -m "Update snprintf vs ctprintf comparison" || exit 0
+                  git push origin gh-pages

README.md

@@ -166,6 +166,9 @@ over time. Results are updated on pushes to `main` and weekly. To publish the
 dashboard, enable GitHub Pages for the repository with the `gh-pages` branch as
 the source.
 
+A direct side-by-side [snprintf vs ctprintf comparison](https://embtom.github.io/ctprintf/comparison.html)
+is generated from the same run by `scripts/benchmark-comparison.py`.
+
 ## Creating a package
 
 CPack creates a gzip-compressed tarball containing the installable headers,

scripts/benchmark-comparison.py

@@ -0,0 +1,58 @@
+#!/usr/bin/env python3
+"""Render a direct snprintf vs ctprintf comparison from Google Benchmark JSON.
+
+Usage: benchmark-comparison.py results.json output.html [summary.md]
+"""
+import html
+import json
+import sys
+from collections import defaultdict
+
+
+def load(path):
+    with open(path) as f:
+        data = json.load(f)
+    times = defaultdict(dict)
+    for b in data["benchmarks"]:
+        if b.get("run_type") == "aggregate" and b.get("aggregate_name") != "mean":
+            continue
+        name = b.get("run_name", b["name"])
+        _, impl, case = name.split("_", 2)
+        times[case][impl] = (b["cpu_time"], b.get("time_unit", "ns"))
+    return {c: v for c, v in times.items() if "snprintf" in v and "ctprintf" in v}
+
+
+def main():
+    cases = load(sys.argv[1])
+    rows = []
+    for case, v in sorted(cases.items()):
+        s, unit = v["snprintf"]
+        c, _ = v["ctprintf"]
+        rows.append((case, s, c, unit, s / c))
+
+    md = ["| Case | snprintf | ctprintf | speedup |", "|---|---|---|---|"]
+    for case, s, c, unit, r in rows:
+        md.append(f"| {case} | {s:.1f} {unit} | {c:.1f} {unit} | {r:.2f}x |")
+    if len(sys.argv) > 3:
+        with open(sys.argv[3], "a") as f:
+            f.write("## snprintf vs ctprintf\n\n" + "\n".join(md) + "\n")
+
+    body = []
+    for case, s, c, unit, r in rows:
+        m = max(s, c)
+        body.append(
+            f"<h2>{html.escape(case)} <small>({r:.2f}x {'faster' if r >= 1 else 'slower'})</small></h2>"
+            f"<div class=bar><div class=sn style='width:{s / m * 100:.1f}%'>snprintf {s:.1f} {unit}</div></div>"
+            f"<div class=bar><div class=ct style='width:{c / m * 100:.1f}%'>ctprintf {c:.1f} {unit}</div></div>"
+        )
+    page = f"""<!doctype html><meta charset=utf-8><title>snprintf vs ctprintf</title>
+<style>body{{font-family:sans-serif;max-width:800px;margin:2em auto}}
+.bar{{background:#eee;margin:4px 0}}.bar div{{padding:4px;color:#fff;white-space:nowrap}}
+.sn{{background:#888}}.ct{{background:#2a7}}small{{font-weight:normal;color:#555}}</style>
+<h1>snprintf vs ctprintf</h1><p>Lower is better (CPU time per call).
+<a href="./">History dashboard</a></p>{''.join(body)}"""
+    with open(sys.argv[2], "w") as f:
+        f.write(page)
+
+
+main()