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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
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arithmetic/output/03-widening-and-biginteger.txt
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$ java WideningAndBigIntegerDemo
=== Widening to long fixes the int-range overflow from OverflowWrapDemo ===
int: Integer.MAX_VALUE + 1 = -2147483648 (wrong)
long: (long) Integer.MAX_VALUE + 1 = 2147483648 (correct)
=== Widening only raises the ceiling - long still overflows eventually ===
Long.MAX_VALUE + 1 = -9223372036854775808 (wrapped to Long.MIN_VALUE - same bug, bigger numbers)
=== BigInteger never overflows - it grows to fit the true value ===
BigInteger.valueOf(Long.MAX_VALUE).add(ONE) = 9223372036854775808
BigInteger.valueOf(2).pow(100) = 1267650600228229401496703205376
(that value has no exact long or int representation at all)