One does not simply calculate the absolute value

Re:One does not simply calculate the absolute value by Sharlin on Sunday August 22, 2021 @06:01PM (#28270082)

Computing the absolute value of a signed (fixed-size, two's complement) integer is not trivial either, because there is no positive i such that `abs(INT_MIN) == i`. Some languages like Java just give you `abs(INT_MIN) == INT_MIN` because:

    -100…000 = ~100…000 + 1 = 011…111 + 1 = 100…000

where ~ is the bitwise complement. Even worse, in C and C++ specifically, because overflow of signed integers is undefined behavior, so is `abs(INT_MIN)`! To be able to represent the absolute value, you need to either return the corresponding unsigned type (if your language has them), promote to a wider type, or return a tuple `(carry_bit, result)`.

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Re:One does not simply calculate the absolute value by nightcracker on Monday August 23, 2021 @01:41AM (#28272645)

This is why Rust has `abs`, `checked_abs`, `wrapping_abs`, `overflowing_abs`, `saturating_abs` and `unsigned_abs`.

Checked returns a Result enum that is an error on overflow, wrapping silently wraps (as in your answer), overflowing wraps but has a boolean indicator whether a wrap has occurred, saturating bounds at the types limits rather than wrapping and unsigned abs always gives the correct result albeit as a different type.

The unqualified abs panics on overflow on debug but silently wraps on release mode, like all Rust arithmetic code does by default.

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