FA-5479 / Integer arithmetic / Member archive

Sum integer range inclusive · case 04

The terminal value is excluded by a half-open iteration.

Member previewVariant 4 · 3 implementations · 4 checks per implementation

Case contract

Integer arguments; denominators, steps, moduli, and bit widths are positive. Unsigned word inputs fit the specified width except where masking is explicitly the operation. Sequence sizes are nonnegative. a<=b; sum every integer in the closed interval. Exact operational definition: (b-a+1)*(a+b)//2

Why this case matters

Small exact fixtures expose this error without platform timing, external services, or probabilistic observations. Integer mathematics results depend on the stated convention.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
fixture 1: (1, 4)	`6`	`10`	Failed

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