• Harry Gillanders (12/12) Apr 28 2020 The spec doesn't seem to explicitly mention what happens when the
• H. S. Teoh (6/11) Apr 28 2020 [...]

Harry Gillanders <ayjsy47yyz8 temp.mailbox.org> writes:

The spec doesn't seem to explicitly mention what happens when the 
left operand
of a shift expression is signed and negative. [1]
But I know that D follows C's semantics for this sort of stuff, 
and the C
standard specifies that the result of a negative left operand is 
undefined
for `<<`, and implementation-defined for `>>`. [2][3]

Is D's behaviour the same as C in this regard?

[1]: https://dlang.org/spec/expression.html#shift_expressions
[2]: https://port70.net/~nsz/c/c89/c89-draft.html#3.3.7
[3]: https://port70.net/~nsz/c/c11/n1570.html#6.5.7

"H. S. Teoh" <hsteoh quickfur.ath.cx> writes:

On Tue, Apr 28, 2020 at 08:30:27PM +0000, Harry Gillanders via
Digitalmars-d-learn wrote:
 The spec doesn't seem to explicitly mention what happens when the left
 operand of a shift expression is signed and negative. [1]
 But I know that D follows C's semantics for this sort of stuff, and
 the C standard specifies that the result of a negative left operand is
 undefined for `<<`, and implementation-defined for `>>`. [2][3]

[...]

Yes, it's UB.  Don't do it.


T

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