1 files changed, 73 insertions, 0 deletions
diff --git a/toolkit/components/telemetry/build_scripts/gen_histogram_phf.py b/toolkit/components/telemetry/build_scripts/gen_histogram_phf.py
new file mode 100644
index 0000000000..38c7245506
--- /dev/null
+++ b/toolkit/components/telemetry/build_scripts/gen_histogram_phf.py
@@ -0,0 +1,73 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+from mozparsers.shared_telemetry_utils import ParserError
+from perfecthash import PerfectHash
+
+PHFSIZE = 1024
+
+import sys
+
+import buildconfig
+from mozparsers import parse_histograms
+
+banner = """/* This file is auto-generated, see gen_histogram_phf.py.  */
+"""
+
+header = """
+#ifndef mozilla_TelemetryHistogramNameMap_h
+#define mozilla_TelemetryHistogramNameMap_h
+
+#include "mozilla/PerfectHash.h"
+
+namespace mozilla {
+namespace Telemetry {
+"""
+
+footer = """
+} // namespace mozilla
+} // namespace Telemetry
+#endif // mozilla_TelemetryHistogramNameMap_h
+"""
+
+
+def main(output, *filenames):
+    """
+    Generate a Perfect Hash Table for the Histogram name -> Histogram ID lookup.
+    The table is immutable once generated and we can avoid any dynamic memory allocation.
+    """
+
+    output.write(banner)
+    output.write(header)
+
+    try:
+        histograms = list(parse_histograms.from_files(filenames))
+        histograms = [
+            h for h in histograms if h.record_on_os(buildconfig.substs["OS_TARGET"])
+        ]
+    except ParserError as ex:
+        print("\nError processing histograms:\n" + str(ex) + "\n")
+        sys.exit(1)
+
+    histograms = [
+        (bytearray(hist.name(), "ascii"), idx) for (idx, hist) in enumerate(histograms)
+    ]
+    name_phf = PerfectHash(histograms, PHFSIZE)
+
+    output.write(
+        name_phf.cxx_codegen(
+            name="HistogramIDByNameLookup",
+            entry_type="uint32_t",
+            lower_entry=lambda x: str(x[1]),
+            key_type="const nsACString&",
+            key_bytes="aKey.BeginReading()",
+            key_length="aKey.Length()",
+        )
+    )
+
+    output.write(footer)
+
+
+if __name__ == "__main__":
+    main(sys.stdout, *sys.argv[1:])