• bearophile (5/5) Jul 31 2014 Is it a good idea to add int/uint/long/ulong functions for the
• H. S. Teoh via Digitalmars-d-learn (7/11) Jul 31 2014 [...]
• bearophile (7/9) Jul 31 2014 If you have a uint where the 3 most significant bits are 1, and
• H. S. Teoh via Digitalmars-d-learn (9/18) Jul 31 2014 [...]
• bearophile (5/11) Jul 31 2014 Of course.

"bearophile" <bearophileHUGS lycos.com> writes:

Is it a good idea to add int/uint/long/ulong functions for the 
"<<" left shift operation here?

https://github.com/D-Programming-Language/druntime/blob/master/src/core/checkedint.d

Bye,
bearophile

"H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:

On Thu, Jul 31, 2014 at 05:00:22PM +0000, bearophile via Digitalmars-d-learn
wrote:
 Is it a good idea to add int/uint/long/ulong functions for the "<<"
 left shift operation here?
 
 https://github.com/D-Programming-Language/druntime/blob/master/src/core/checkedint.d

[...]

What would you check for? Shifting something that already has its high
bit set?


T

-- 
Don't drink and derive. Alcohol and algebra don't mix.

"bearophile" <bearophileHUGS lycos.com> writes:

H. S. Teoh:

 What would you check for? Shifting something that already has 
 its high bit set?

If you have a uint where the 3 most significant bits are 1, and 
you shift it 3 bits on the left, you lose those three bits, you 
have an overflow. The point of checkedint functions/intrinsics is 
to reveal overflows.

Bye,
bearophile

"H. S. Teoh via Digitalmars-d-learn" <digitalmars-d-learn puremagic.com> writes:

On Thu, Jul 31, 2014 at 06:08:56PM +0000, bearophile via Digitalmars-d-learn
wrote:
 H. S. Teoh:
 
What would you check for? Shifting something that already has its
high bit set?

 
 If you have a uint where the 3 most significant bits are 1, and you
 shift it 3 bits on the left, you lose those three bits, you have an
 overflow. The point of checkedint functions/intrinsics is to reveal
 overflows.

[...]

OK, makes sense. But what about if only the most significant bit is 1?
Wouldn't that also be an overflow? So you're essentially checking if the
topmost n bits are zero, where n is the number of bits you wish to shift
by.


T

-- 
BREAKFAST.COM halted...Cereal Port Not Responding. -- YHL

"bearophile" <bearophileHUGS lycos.com> writes:

H. S. Teoh:

 OK, makes sense. But what about if only the most significant 
 bit is 1?
 Wouldn't that also be an overflow? So you're essentially 
 checking if the
 topmost n bits are zero, where n is the number of bits you wish 
 to shift by.

Of course.

https://issues.dlang.org/show_bug.cgi?id=13231

Bye,
bearophile