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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/01-overflow-wrap.txt
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$ java OverflowWrapDemo
=== int addition wraps silently past Integer.MAX_VALUE ===
Integer.MAX_VALUE = 2147483647
Integer.MAX_VALUE + 1 = -2147483648 (wrapped to Integer.MIN_VALUE, no exception)
Integer.MIN_VALUE = -2147483648
=== A realistic case: summing item prices in cents overflows int ===
priceCents * quantity = 1800000000 * 2 = -694967296 (should be 3,600,000,000 - this is wrong, and no exception was thrown)
=== Multiplication overflows just as silently as addition ===
100000 * 100000 = 1410065408 (true value is 10,000,000,000)
=== long has the same problem, just a much higher ceiling ===
Long.MAX_VALUE = 9223372036854775807
Long.MAX_VALUE + 1 = -9223372036854775808 (wrapped to Long.MIN_VALUE)