arithmetic: companion code for the Add Two Numbers Without Overflow post

Silent int/long overflow reproduced with real numbers, the Math *Exact() family (addExact/subtractExact/multiplyExact/incrementExact/decrementExact/ negateExact/toIntExact/absExact) with the abs(MIN_VALUE) trap absExact exists to catch, widening to long vs BigInteger, and the XOR-based overflow bit trick Math.addExact uses internally, cross-checked against BigInteger ground truth over 100k random int pairs per JUnit repeat. Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01FhzLY5p6okFva3qsnsRyvM
2026-09-30 09:16:49 +00:00
parent 202f2f18a5
commit af615cc17c
15 changed files with 514 additions and 0 deletions
@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+# Regenerates every file in ../output/ from a real run against $JDK25_HOME.
+# Usage: JDK25_HOME=/path/to/jdk-25 ./run-all.sh
+set -euo pipefail
+
+if [ -z "${JDK25_HOME:-}" ]; then
+  echo "Set JDK25_HOME to a JDK 25 install first." >&2
+  exit 1
+fi
+
+cd "$(dirname "$0")/.."
+OUT="output"
+mkdir -p "$OUT"
+
+"$JDK25_HOME/bin/mvn" -q -f pom.xml package 2>/dev/null || true
+CP="target/classes"
+if [ ! -d "$CP" ]; then
+  mkdir -p target/classes
+  "$JDK25_HOME/bin/javac" -d target/classes $(find src/main/java -name '*.java')
+fi
+
+run() {
+  local cls="$1" out="$2"
+  echo "\$ java $cls" > "$OUT/$out"
+  echo >> "$OUT/$out"
+  "$JDK25_HOME/bin/java" -cp "$CP" "com.ankurm.arithmetic.$cls" >> "$OUT/$out" 2>&1
+}
+
+run OverflowWrapDemo            01-overflow-wrap.txt
+run ExactArithmeticDemo         02-exact-arithmetic.txt
+run WideningAndBigIntegerDemo   03-widening-and-biginteger.txt
+run OverflowBitTrickDemo        04-overflow-bit-trick.txt
+
+mkdir -p target/test-classes
+"$JDK25_HOME/bin/javac" -cp "target/classes:$(find / -name 'junit-jupiter-*.jar' 2>/dev/null | tr '\n' ':')" \
+  -d target/test-classes $(find src/test/java -name '*.java') 2>/dev/null || true
+
+"$JDK25_HOME/bin/mvn" -q -f pom.xml test > "$OUT/05-correctness-tests.txt" 2>&1 || true
+cp target/surefire-reports/com.ankurm.arithmetic.ArithmeticClaimsTest.txt "$OUT/05-correctness-tests.txt" 2>/dev/null || true
+
+echo "Done. See $OUT/"