Replace int128_t high word with uint64_t

.github/scripts/compare_benchmarks.sh

@@ -0,0 +1,22 @@
+#!/bin/bash
+# Copyright 2026 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+#
+# Reports the data sets in $1 against the numbers committed under
+# doc/modules/ROOT/data and appends the report to the job summary. Run it from
+# the root of the library checkout.
+#
+# This is informational only: shared runners drift by a few percent from run to
+# run, so a slower number is a prompt to look, not a build failure.
+
+set -e
+
+RESULTS=${1:-bench-results}
+
+PYTHON=python3
+if ! command -v python3 > /dev/null 2>&1; then
+    PYTHON=python
+fi
+
+"$PYTHON" doc/render_benchmarks.py --compare "$RESULTS" --summary "${GITHUB_STEP_SUMMARY:-/dev/null}"

.github/scripts/run_benchmarks.sh

@@ -0,0 +1,89 @@
+#!/bin/bash
+# Copyright 2026 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+#
+# Builds both benchmark drivers in release mode and runs them, leaving u128.json
+# and i128.json in the --out directory. Those two files are exactly what
+# doc/render_benchmarks.py consumes.
+#
+# Run it from the root of a Boost tree that has this library in libs/int128; the
+# include path is every libs/*/include in that tree, so no b2 headers step is
+# needed. The drivers always exit non-zero (the Jamfile declares them run-fail),
+# so success is judged on the data set actually being written.
+#
+#   .github/scripts/run_benchmarks.sh --compiler g++-14 --out /tmp/results
+#   .github/scripts/run_benchmarks.sh --msvc --elements 5000000 --out C:/results
+
+set -e
+
+COMPILER=""
+EXTRA_CXXFLAGS=""
+EXTRA_LDFLAGS=""
+ELEMENTS=20000000
+REPETITIONS=5
+OUT=""
+MSVC=0
+
+while [ $# -gt 0 ]; do
+    case "$1" in
+        --compiler)    COMPILER="$2"; shift 2 ;;
+        --cxxflags)    EXTRA_CXXFLAGS="$2"; shift 2 ;;
+        --ldflags)     EXTRA_LDFLAGS="$2"; shift 2 ;;
+        --elements)    ELEMENTS="$2"; shift 2 ;;
+        --repetitions) REPETITIONS="$2"; shift 2 ;;
+        --out)         OUT="$2"; shift 2 ;;
+        --msvc)        MSVC=1; shift ;;
+        *) echo "unknown argument: $1" >&2; exit 2 ;;
+    esac
+done
+
+if [ -z "$OUT" ]; then
+    echo "error: --out is required" >&2
+    exit 2
+fi
+
+if [ ! -d libs/int128/test ]; then
+    echo "error: run this from the root of a Boost tree holding libs/int128" >&2
+    exit 2
+fi
+
+mkdir -p "$OUT"
+
+# Every dependency is header only from the benchmarks' point of view, so the
+# include path is simply all of the libraries checked out in this tree.
+INCLUDES=""
+for dir in libs/*/include libs/*/*/include; do
+    if [ -d "$dir" ]; then
+        INCLUDES="$INCLUDES -I$dir"
+    fi
+done
+
+for sign in u128 i128; do
+    source_file="libs/int128/test/benchmark_$sign.cpp"
+
+    if [ "$MSVC" = 1 ]; then
+        # LARGEADDRESSAWARE lets the 32-bit build address more than 2GB, which
+        # the widest vectors need.
+        executable="./benchmark_$sign.exe"
+        # shellcheck disable=SC2086
+        cl -nologo -std:c++20 -O2 -EHsc -DNDEBUG $INCLUDES "$source_file" \
+            -Fe:"benchmark_$sign.exe" -link -LARGEADDRESSAWARE
+    else
+        executable="./benchmark_$sign"
+        # shellcheck disable=SC2086
+        $COMPILER -std=c++20 -O2 -DNDEBUG $EXTRA_CXXFLAGS $INCLUDES "$source_file" \
+            -o "benchmark_$sign" $EXTRA_LDFLAGS
+    fi
+
+    echo "==================== benchmark_$sign ===================="
+    "$executable" --elements "$ELEMENTS" --repetitions "$REPETITIONS" --json "$OUT/$sign.json" || true
+
+    if [ ! -s "$OUT/$sign.json" ]; then
+        echo "error: benchmark_$sign did not write $OUT/$sign.json" >&2
+        exit 1
+    fi
+done
+
+echo "==================== data sets ===================="
+ls -l "$OUT"

.github/scripts/setup_benchmarks.sh

@@ -0,0 +1,42 @@
+#!/bin/bash
+# Copyright 2026 Matt Borland
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+#
+# Clones a Boost tree next to the checkout, drops this library into it, and
+# installs the dependencies the benchmarks need. Exports BOOST_ROOT for the
+# steps that follow. Only used by .github/workflows/benchmarks.yml.
+
+set -e
+
+LIBRARY=${GITHUB_REPOSITORY#*/}
+REF=${GITHUB_BASE_REF:-$GITHUB_REF}
+REF=${REF#refs/heads/}
+
+BOOST_BRANCH=develop
+if [ "$REF" = "master" ]; then
+    BOOST_BRANCH=master
+fi
+
+PYTHON=python3
+if ! command -v python3 > /dev/null 2>&1; then
+    PYTHON=python
+fi
+
+cd ..
+git clone -b "$BOOST_BRANCH" --depth 1 https://github.com/boostorg/boost.git boost-root
+cd boost-root
+mkdir -p "libs/$LIBRARY"
+
+# Everything except doc/: it carries an Antora examples symlink that git-bash on
+# Windows cannot recreate, plus a node_modules tree that nothing here needs.
+for entry in "$GITHUB_WORKSPACE"/*; do
+    if [ "$(basename "$entry")" != doc ]; then
+        cp -r "$entry" "libs/$LIBRARY/"
+    fi
+done
+
+git submodule update --init tools/boostdep
+"$PYTHON" tools/boostdep/depinst/depinst.py --git_args "--jobs ${GIT_FETCH_JOBS:-4}" "$LIBRARY"
+
+echo "BOOST_ROOT=$(pwd)" >> "$GITHUB_ENV"