The relevant bit of the Haskell report:

18.1 Signed integer types

This module provides signed integer types of unspecified width (Int) and fixed widths (Int8, Int16, Int32 and Int64). All arithmetic is performed modulo 2^n, where n is the number of bits in the type.

Link: https://www.haskell.org/onlinereport/haskell2010/haskellch18.html#x26-223000... The module 2^n bit is ambiguous to me, but it seems it's just doing 2's complement, which is what the underlying machine does: (maxBound :: Int8) + 1 -128 The C standard, by contrast, states that the behavior of signed-arithmetic overflow is *undefined*, which is to say there are absolutely *NO* constraints on what the compiler can do. Modern compilers use this fact to assume this will never happen when optimizing. I actually get different numbers with your C example depending on what optimization flags I pass to the compiler. Worth noting, this is a huge source of security vulnerabilities in C & C++. -Ian Quoting Matt Peddie (2019-02-27 17:41:43)

Hi cafe,

It's been my general impression that when neither Haskell nor C defines behavior in a particular situation, the behavior nonetheless matches. I was surprised to observe

Prelude Data.Int> round (4294967295 :: Double) :: Int16 -1

when

#include #include int main(void) { double d = 4294967295; int16_t r = (int16_t) d; printf("%"PRId16"\n", r); return 0; }

yields 0 when compiled and run.

As far as I can tell, neither language defines what this result should be, so neither is doing anything wrong here. But I was surprised that they differ; does anyone know why Haskell's rounding operation behaves the way it does (maybe there is some historical reason)? Or can someone perhaps point me to a standards document I missed that states how the language must round out-of-bounds inputs?

Regards

Matt Peddie _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.