On 04/04/2024 16:39, J. Gareth Moreton via fpc-devel wrote:
Essentially, an arithmetic overflow is happening. Since the largest
Int64 possible is 9,223,372,036,853,775,807, going one above that (the
result to abs(low(int64))) wraps back around to
-9,223,372,036,853,775,808.
Internally, you can think about negating (positing?) a negative number
as inverting the bits and then adding one (aka. two's complement), so
low(int64) is 1000...000, which inverted becomes 0111...111, and then
adding one results in 1000...000 again.
I got that bit...
Initially I was surprised to find "abs" to return a signed number. After
all, it will never be negative.
But, in the meantime I recalled that unsigned numbers will cause other
issues when used in expressions.
"abs(-1)-2" would behave different.
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