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digitalmars.D.announce - core.checkedint added to druntime

reply Walter Bright <newshound2 digitalmars.com> writes:
https://github.com/D-Programming-Language/druntime/pull/839

While being a very modest piece of code in and of itself, I believe this offers 
a significant opportunity that both D compilers and user defined types can
exploit.

Not only can it be used to create an efficient safeint data type, it can be
used 
to implement multi-precision integer arithmetic types.

I'd also like to see it used to replace the various ad-hoc schemes currently in 
use. It should also be used in dmd itself for things like detecting array size 
overflows, which is currently done ad-hoc, and detecting overflows in CTFE.

For background information and rationale, see
http://blog.regehr.org/archives/1139
Jun 17 2014
next sibling parent reply "bearophile" <bearophileHUGS lycos.com> writes:
Walter Bright:


 https://github.com/D-Programming-Language/druntime/pull/839


Why aren't functions with ubyte/byte/short/ushort arguments 
included?

--------------

Here Lionello Lunesu has suggested a __traits(valueRange, 
<expression>) for built-in values:
http://forum.dlang.org/thread/lnrc8l$1254$1 digitalmars.com

Once such trait is working on checkedint values, can this help 
the compiler remove some useless tests and increase the 
performance of checked ints?



 it can be used to implement multi-precision integer arithmetic 
 types.


It looks very useful for the "small value optimization" for 
BigIntegers, to not allocate on the heap when the numbers are 
small, and switch to the heap allocation when they grow.

If you use such improved bigintegers to write code that is not 
supposed to overflow the range of normal integers, you obtain 
code that is only moderately slower than using checkedints, but 
it also gives the correct results if some overflow has occurred 
:-)

Bye,
bearophile
Jun 18 2014
parent reply Walter Bright <newshound2 digitalmars.com> writes:
On 6/18/2014 2:43 AM, bearophile wrote:

 Walter Bright:


 https://github.com/D-Programming-Language/druntime/pull/839


 Why aren't functions with ubyte/byte/short/ushort arguments included?


Because there is no ubyte/byte/short/ushort math in C, C++ or D. There is only 
int/long math.
Jun 18 2014
parent "bearophile" <bearophileHUGS lycos.com> writes:
Walter Bright:


 Because there is no ubyte/byte/short/ushort math in C, C++ or 
 D. There is only int/long math.


A little of ubyte math is present, perhaps for this you add 
"uinc", "sinc", "udec", "sdec" functions to core.checkedint that 
support ubyte/byte/short/ushort types too:

void main() {
     ubyte x = 100;
     x++;
}


But you are right, in D if you sum two ubytes you get an int:

void main() {
     ubyte x = 100;
     ubyte y = 200;
     pragma(msg, typeof(x + y)); // Prints "int"
}


Yet sometimes you want to perform safe math operations on 
ubytes/bytes/shorts/ushorts, and keep the same type for the 
results. So I presume a future Phobos Safe math based on 
core.checkedint will need to check the ranges by itself, to allow 
checked assignments back to the same types:

void main() {
     Safe!ubyte x = 100;
     Safe!ubyte y = 200;
     Safe!ubyte z = x + y;
}

Bye,
bearophile
Jun 18 2014
prev sibling next sibling parent reply "David Bregman" <drb sfu.ca> writes:
On Wednesday, 18 June 2014 at 01:26:16 UTC, Walter Bright wrote:

 https://github.com/D-Programming-Language/druntime/pull/839


I think the mulu implementation is incorrect. There can be an 
overflow even when r = 0. For example consider the int version 
with x = y = 1<<16.
Jun 18 2014
parent "David Nadlinger" <code klickverbot.at> writes:
On Thursday, 19 June 2014 at 03:42:11 UTC, David Bregman wrote:

 I think the mulu implementation is incorrect. There can be an 
 overflow even when r = 0. For example consider the int version 
 with x = y = 1<<16.


I also noticed this; another easy counter-example would be 1<<32 
for ulong multiplication.

Filed as: https://issues.dlang.org/show_bug.cgi?id=12958
Jun 20 2014
prev sibling next sibling parent reply =?UTF-8?B?Ik5vcmRsw7Z3Ig==?= <per.nordlow gmail.com> writes:
 While being a very modest piece of code in and of itself, I 
 believe this offers a significant opportunity that both D 
 compilers and user defined types can exploit.


I did this in C/C++ a while ago, out of which I have forgotten 
most of it :)

https://github.com/nordlow/justcxx/blob/master/sadd.h
https://github.com/nordlow/justcxx/blob/master/ssub.h
https://github.com/nordlow/justcxx/blob/master/smul.h

Tests are here:
https://github.com/nordlow/justcxx/blob/master/t_ranged_and_saturated.cpp

Maybe there's something more here that could give further ideas.

Pick what you want.
Jun 22 2014
parent Walter Bright <newshound2 digitalmars.com> writes:
On 6/22/2014 12:37 AM, "Nordlöw" wrote:

 While being a very modest piece of code in and of itself, I believe this
 offers a significant opportunity that both D compilers and user defined types
 can exploit.


 I did this in C/C++ a while ago, out of which I have forgotten most of it :)

 https://github.com/nordlow/justcxx/blob/master/sadd.h
 https://github.com/nordlow/justcxx/blob/master/ssub.h
 https://github.com/nordlow/justcxx/blob/master/smul.h

 Tests are here:
 https://github.com/nordlow/justcxx/blob/master/t_ranged_and_saturated.cpp

 Maybe there's something more here that could give further ideas.

 Pick what you want.


Thank you, that's very generous.
Jun 22 2014
prev sibling parent reply "Paul D Anderson" <claude.rains msn.com> writes:
Will this be in the 2.066 Beta?

On Wednesday, 18 June 2014 at 01:26:16 UTC, Walter Bright wrote:

 https://github.com/D-Programming-Language/druntime/pull/839

 While being a very modest piece of code in and of itself, I 
 believe this offers a significant opportunity that both D 
 compilers and user defined types can exploit.

 Not only can it be used to create an efficient safeint data 
 type, it can be used to implement multi-precision integer 
 arithmetic types.

 I'd also like to see it used to replace the various ad-hoc 
 schemes currently in use. It should also be used in dmd itself 
 for things like detecting array size overflows, which is 
 currently done ad-hoc, and detecting overflows in CTFE.

 For background information and rationale, see 
 http://blog.regehr.org/archives/1139
Jul 01 2014
parent "David Nadlinger" <code klickverbot.at> writes:
On Tuesday, 1 July 2014 at 22:07:01 UTC, Paul D Anderson wrote:

 Will this be in the 2.066 Beta?


It's currently in Git master, so yes – but we definitely need to 
fix https://issues.dlang.org/show_bug.cgi?id=12958 before the 
release (mul is horribily broken).

David
Jul 01 2014