• akcom <CppCoder gmail.com> Apr 19 2006
• Ryan Steen <Ryan_member pathlink.com> Apr 19 2006
• akcom <CppCoder gmail.com> Apr 20 2006
• Don Clugston <dac nospam.com.au> Apr 20 2006
• akcom <CppCoder gmail.com> Apr 20 2006

akcom <CppCoder gmail.com> writes:

I apologize if this is an easily resolved problem, this is my first
attempt at writing a template function.  the objective of this function
is to mimic the behavior of the AP hash function, but as a template
function obviously.  Here is what I have so far:

uint aphash( ubyte []buf )
{
	uint hash;
	
	for ( uint i = 0; i < buf.length; i++ )
	{
		hash ^= ((i & 1) == 0) ?	(  (hash <<  7) ^ (buf[i]) ^ (hash >> 3)) :
									(~((hash << 11) ^ (buf[i]) ^ (hash >> 5)));
	}
	return hash;
}

template aphasht( T : ubyte [] )
{
	uint aphasht( T t )
	{
		uint result;
		static if ( t.length == 0 )
		{
			return 0;
		}
		static if ( t.length & 1 )
		{
			result = aphasht( t[1..$] );
			return (result << 7) ^ t[0] ^ (result >> 3);
		}
		else
		{
			result = aphasht( t[1..$] );
			return (result << 11) ^ t[0] ^ (result >> 5);
		}
	}
}

void test()
{
	static ubyte []str = [ 0x01, 0x02, 0x03, 0x03 ];
	writefln( "aphash(str) = %X", aphash( str ) );
	writefln( "aphasht(str) = %X", aphasht!(ubyte [])( str ) );
}


When I attempt to compile it, I get the following errors:

dmd -w -c main.d
main.d(49): expression ((t).length) == 0u does not evaluate to a boolean
main.d(53): expression ((t).length) & 1u does not evaluate to a boolean
main.d(70): template instance main.aphasht!(ubyte[]) error instantiating

Could someone please point out my mistake, and if there is a more
elegant way of completing this task, I'd appreciate some input on that
as well.

Regards,
Alex

Ryan Steen <Ryan_member pathlink.com> writes:

In article <e26v01$2m8$1 digitaldaemon.com>, akcom says...

		static if ( t.length == 0 )
		static if ( t.length & 1 )
main.d(49): expression ((t).length) == 0u does not evaluate to a boolean
main.d(53): expression ((t).length) & 1u does not evaluate to a boolean


"It is an error if AssignExpression ... cannot be evaluated at compile time."

akcom <CppCoder gmail.com> writes:

Ryan Steen wrote:
 In article <e26v01$2m8$1 digitaldaemon.com>, akcom says...
 
 
		static if ( t.length == 0 )
		static if ( t.length & 1 )
main.d(49): expression ((t).length) == 0u does not evaluate to a boolean
main.d(53): expression ((t).length) & 1u does not evaluate to a boolean


 
 "It is an error if AssignExpression ... cannot be evaluated at compile time."
 
 

Don Clugston <dac nospam.com.au> writes:

akcom wrote:
 Ryan Steen wrote:
 In article <e26v01$2m8$1 digitaldaemon.com>, akcom says...


 		static if ( t.length == 0 )
 		static if ( t.length & 1 )
 main.d(49): expression ((t).length) == 0u does not evaluate to a boolean
 main.d(53): expression ((t).length) & 1u does not evaluate to a boolean


 "It is an error if AssignExpression ... cannot be evaluated at compile time."




It's just because array literals are only supported at this time for 
strings. (Your code might work in DMD 2.0).

If you change the definitions to
const char [] str = x"01 02 03";

template aphasht( char [] T)
{
	const uint aphasht = ...
}
(changing returns to const aphasht).

it would work with

writefln( "aphasht(str) = %X", aphasht!(str ) );

akcom <CppCoder gmail.com> writes:

Don Clugston wrote:
 akcom wrote:
 
 Ryan Steen wrote:

 In article <e26v01$2m8$1 digitaldaemon.com>, akcom says...


         static if ( t.length == 0 )
         static if ( t.length & 1 )
 main.d(49): expression ((t).length) == 0u does not evaluate to a
 boolean
 main.d(53): expression ((t).length) & 1u does not evaluate to a boolean



 "It is an error if AssignExpression ... cannot be evaluated at
 compile time."




 
 It's just because array literals are only supported at this time for
 strings. (Your code might work in DMD 2.0).
 
 If you change the definitions to
 const char [] str = x"01 02 03";
 
 template aphasht( char [] T)
 {
     const uint aphasht = ...
 }
 (changing returns to const aphasht).
 
 it would work with
 
 writefln( "aphasht(str) = %X", aphasht!(str ) );


I finally got it working, but for some odd reason the templates gives
different results than the original function when the string being
processed has a length that is odd, any ideas?

uint aphash( char []buf )
{
	uint hash;
	
	hash = 0;
	for ( uint i = 0; i < buf.length; i++ )
	{
		hash ^= ((i & 1) == 0) ?	(  (hash <<  7) ^ (cast(ubyte)buf[i]) ^ (hash
 3)) :




	}
	return hash;
}

template aphashT( char []s, uint lastHash = 0 )
{
	static if ( s.length == 0 )
	{
		const aphashT = lastHash;
	}
	else static if ( s.length & 1 )
	{
		const aphashT = aphashT!( s[1..$], lastHash ^ ~( (lastHash << 11) ^
cast(ubyte)(s[0]) ^ (lastHash >> 5) ) );
	}
	else
	{
		const aphashT = aphashT!( s[1..$], lastHash ^ ( (lastHash << 7) ^
cast(ubyte)(s[0]) ^ (lastHash >>3) ) );
	}
}

unittest
{
	assert( aphashT!( "aaa" ) == aphash( "aaa" ) ); //fails
	assert( aphashT!( "abcdefg12345" ) == aphash( "abcdefg12345" ) );
	assert( aphashT!( "rofl haxor" ) == aphash( "rofl haxor" ) );
	assert( aphashT!( "abc" ) == aphash( "abc" ) );
	assert( aphashT!( "hello world" ) == aphash( "hello world" ) ); //fails
}