• 2ud5icomjs0t sneakemail.com (10/10) Apr 02 2005 Hi,
• Walter (8/16) Apr 02 2005 bits of
• 2ud5icomjs0t sneakemail.com (5/25) Apr 02 2005 Yes, of course it does, but it is very inconvenient when it comes to set...
• Regan Heath (42/74) Apr 02 2005 Packed bits can be represented by a bit[], BUT, a bit[] is a struct in t...
• brad beveridge (7/14) Apr 02 2005 At first I thought that this was a limitation also, but

2ud5icomjs0t sneakemail.com writes:

Hi,

I'm accessing a hardware port and one of the fields map to the upper 6 bits of
the second byte: 

0123456701234567
aaaaaaaabcdddddd

In C I would use a union between teh 16-bit value and a struct with bitfields,
but http://www.digitalmars.com/d/struct.html explicitly says not bitfields. 

How can I do this in D? 

Can I use array of 'bit' type? If I put these into a struct, will they pack?

Thanks. n

"Walter" <newshound digitalmars.com> writes:

<2ud5icomjs0t sneakemail.com> wrote in message
news:d2njii$1gsc$1 digitaldaemon.com...
 Hi,

 I'm accessing a hardware port and one of the fields map to the upper 6

bits of
 the second byte:

 0123456701234567
 aaaaaaaabcdddddd

 In C I would use a union between teh 16-bit value and a struct with

bitfields,
 but http://www.digitalmars.com/d/struct.html explicitly says not

bitfields.
 How can I do this in D?

Shift & mask ought to do it:

    ushort* p;
    (*p >> 10) & 0x3F

2ud5icomjs0t sneakemail.com writes:

In article <d2nqqn$1mj3$1 digitaldaemon.com>, Walter says...
<2ud5icomjs0t sneakemail.com> wrote in message
news:d2njii$1gsc$1 digitaldaemon.com...
 Hi,

 I'm accessing a hardware port and one of the fields map to the upper 6

bits of
 the second byte:

 0123456701234567
 aaaaaaaabcdddddd

 In C I would use a union between teh 16-bit value and a struct with

bitfields,
 but http://www.digitalmars.com/d/struct.html explicitly says not

bitfields.
 How can I do this in D?

Shift & mask ought to do it:

    ushort* p;
    (*p >> 10) & 0x3F

Yes, of course it does, but it is very inconvenient when it comes to setting
command and data values and toggling handshake bits.

Is there no way to pack bit arrays together?

Thanks. n

"Regan Heath" <regan netwin.co.nz> writes:

On Sun, 3 Apr 2005 05:44:45 +0000 (UTC), <2ud5icomjs0t sneakemail.com>  
wrote:
 In article <d2nqqn$1mj3$1 digitaldaemon.com>, Walter says...
 <2ud5icomjs0t sneakemail.com> wrote in message
 news:d2njii$1gsc$1 digitaldaemon.com...
 Hi,

 I'm accessing a hardware port and one of the fields map to the upper 6

 bits of
 the second byte:

 0123456701234567
 aaaaaaaabcdddddd

 In C I would use a union between teh 16-bit value and a struct with

 bitfields,
 but http://www.digitalmars.com/d/struct.html explicitly says not

 bitfields.
 How can I do this in D?

 Shift & mask ought to do it:

    ushort* p;
    (*p >> 10) & 0x3F

 Yes, of course it does, but it is very inconvenient when it comes to  
 setting
 command and data values and toggling handshake bits.

 Is there no way to pack bit arrays together?

 Thanks. n

Packed bits can be represented by a bit[], BUT, a bit[] is a struct in the  
form:

struct array {
   uint length;
   void *data;
}

and when you say "bit[] bits" you're creating a reference to an array of  
bits. So

union {
   uint mask;
   bit[] bits;
}

places a uint and a "reference" to an array of bits in the same memory  
space. The problem here is that the data referenced by the array is  
elsewhere (actually null/undefined at present).

You can however at any time slice a bit* to obtain a bit[] (same holds for  
other ptr types, int* to int[], etc). You can also cast the address of any  
basic type byte, short, int, long (and the unsigned variants) to a bit*,  
so...

import std.stdio;

struct foo {
	ushort mask;
}

void main()
{
	bit[] bits;
	foo a;
	
	a.mask = 0b1101101101101101;
	bits = (cast(bit*)&a.mask)[0..16];
	foreach(bit b; bits)
		writef("%d",b);
	writefln("");
}

Output:
1011011011011011

(note, it looks reversed but that is because it iterates from bit[0] to  
bit[15], LSB to MSB (most significant bit), meaning it goes from right to  
left.

Regan

brad beveridge <brad nowhere.com> writes:

 
 Yes, of course it does, but it is very inconvenient when it comes to setting
 command and data values and toggling handshake bits.
 
 Is there no way to pack bit arrays together?
 
 Thanks. n

At first I thought that this was a limitation also, but
  1) This kind of bit packing in C introduces behind the scenes 
operations, which - especially for hardware mapped devices - may fool 
the programmer into thinking about the code wrong
  2) The bit field packing can be simulated in D using properties, so 
that the usage code will look just like C code.

Brad