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

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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
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asmhatre
2026-09-30 09:16:49 +00:00
co-authored by Claude Sonnet 5
parent 202f2f18a5
commit af615cc17c
15 changed files with 514 additions and 0 deletions
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arithmetic/output/04-overflow-bit-trick.txt
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$ java OverflowBitTrickDemo
=== Hand-rolled overflow detector vs. known cases ===
2000000000 + 2000000000 -> raw int result -294967296, overflow detected: true
2000000000 + -1000000000 -> raw int result 1000000000, overflow detected: false
2147483647 + 1 -> raw int result -2147483648, overflow detected: true
-2147483648 + -1 -> raw int result 2147483647, overflow detected: true
100 + 200 -> raw int result 300, overflow detected: false
=== Cross-checked against Math.addExact() on the same inputs ===
2000000000 + 2000000000: bit-trick says overflow=true, Math.addExact() agrees=true
2000000000 + -1000000000: bit-trick says overflow=false, Math.addExact() agrees=true
2147483647 + 1: bit-trick says overflow=true, Math.addExact() agrees=true
-2147483648 + -1: bit-trick says overflow=true, Math.addExact() agrees=true
100 + 200: bit-trick says overflow=false, Math.addExact() agrees=true