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D - Bit fields

reply "Rolf Campbell" <rolf.campbell tropicnetworks.com> writes:
Quote from overview:

Features To Drop
-Bit fields of arbitrary size. Bit fields are a complex, inefficient feature
rarely used.

 You mention that you want to have 'D' be able to directly interface with
hardware, "...retains the ability to write high performance code and
interface directly with the operating system APIs and with hardware."

Many types of hardware (and file-formats) make use of bit-fields in their
structures.  While it is always possible to make masks and bit shift stuff
yourself, it is more prone to error than using bit-fields.  I think that
bit-fields are a part of the compiler which many people will implement
themselves if it's not included (kinda like string class in C++).

-Rolf Campbell
Aug 16 2001
next sibling parent weingart cs.ualberta.ca (Tobias Weingartner) writes:
In article <9lgqhk$2clv$1 digitaldaemon.com>, Rolf Campbell wrote:
 Quote from overview:
 
 Features To Drop
 -Bit fields of arbitrary size. Bit fields are a complex, inefficient feature
 rarely used.
 
  You mention that you want to have 'D' be able to directly interface with
 hardware, "...retains the ability to write high performance code and
 interface directly with the operating system APIs and with hardware."

This is one problem. However, if you have bitfields, please define the ordering that they will have bits in. Bitfields are not portable in C/C++ due to this fact. All OS software needs to use masks/etc to write "portable" drivers in C.
 Many types of hardware (and file-formats) make use of bit-fields in their
 structures.  While it is always possible to make masks and bit shift stuff
 yourself, it is more prone to error than using bit-fields.  I think that
 bit-fields are a part of the compiler which many people will implement
 themselves if it's not included (kinda like string class in C++).

This again is very true. I would recommend having some sort of bitfield mechanism, along with some mechanism to access memory and I/O ports. This could well be implemented in modules (using assembly language) on each port of the language. With automatic inlining (and link-optimization passes), this could be as good, or better than language support for the various "machine oriented" constructs. In other words, have a bitfield module, that implements both LE, BE, and other ordering for bitfields. -- Tobias Weingartner | Unix Guru, Admin, Systems-Dude Apt B 7707-110 St. | http://www.tepid.org/~weingart/ Edmonton, AB |------------------------------------------------- Canada, T6G 1G3 | %SYSTEM-F-ANARCHISM, The OS has been overthrown
Aug 16 2001
prev sibling parent reply Matt Gessner <mattg aiinet.com> writes:
Rolf Campbell wrote:

 Quote from overview:
 
 Features To Drop
 -Bit fields of arbitrary size. Bit fields are a complex, inefficient feature
 rarely used.
 
  You mention that you want to have 'D' be able to directly interface with
 hardware, "...retains the ability to write high performance code and
 interface directly with the operating system APIs and with hardware."
 
 Many types of hardware (and file-formats) make use of bit-fields in their
 structures.  While it is always possible to make masks and bit shift stuff
 yourself, it is more prone to error than using bit-fields.  I think that
 bit-fields are a part of the compiler which many people will implement
 themselves if it's not included (kinda like string class in C++).
 
 -Rolf Campbell
 
 
 

Hear, hear! I write embedded systems for a living, and most of the configuration and status registers are implemented with a bit here and a couple of bits there. This is an extremely useful language feature in doing embedded systems. Matt
Aug 16 2001
parent reply "Walter" <walter digitalmars.com> writes:
"Matt Gessner" <mattg aiinet.com> wrote in message
news:3B7C19A7.3040203 aiinet.com...
 Rolf Campbell wrote:
 Quote from overview:
 Features To Drop
 -Bit fields of arbitrary size. Bit fields are a complex, inefficient


 rarely used.

  You mention that you want to have 'D' be able to directly interface


 hardware, "...retains the ability to write high performance code and
 interface directly with the operating system APIs and with hardware."

 Many types of hardware (and file-formats) make use of bit-fields in


 structures.  While it is always possible to make masks and bit shift


 yourself, it is more prone to error than using bit-fields.  I think that
 bit-fields are a part of the compiler which many people will implement
 themselves if it's not included (kinda like string class in C++).

 -Rolf Campbell


 and status registers are implemented with a bit here and a couple of bits

 This is an extremely useful language feature in doing embedded systems.
 Matt

When I've done hardware I/O, I always wound up doing masking and shifting, because it produced better code.
Aug 16 2001
parent "Robert W. Cunningham" <rwc_2001 yahoo.com> writes:
Walter wrote:

 When I've done hardware I/O, I always wound up doing masking and shifting,
 because it produced better code.

Yes, but debugging massive bit twiddling for things like long bit strings to SPI devices quickly becomes a nightmare. It would truly be beneficial to have the D "bit" type enhanced for packing into fundamental integer types (and arrays of same). One big problem is that the same D code must compile and run on platforms with different endian-ness! The same hardware chip (say, an Ethernet controller) with a mix of 8/16/32-bit registers soon becomes a nightmare, depending on if the device is accessed by byte, word or dword. The situation in C often requires special macros to handle endian-ness, or (worse) a mess of conditionally compiled code. Another embedded perspective: It would be good to define ways of writing D code that will GUARANTEE the garbage collector will NOT be invoked! Perhaps a compiler switch to disable both GC and the language features that rely upon it. I'd willing accept a restricted language subset for certain circumstances (say, device drivers and interrupt handlers) if it will allow me to program an entire system in a single language. When using C, I often result to inline assembly ("asm(...)") to handle cases the language can't handle well. But this makes the code inherently non-portable, so I always wind up including the messy C equivalent in a #ifdef'ed code section ("#ifdef NOASM ..."). -BobC
Aug 16 2001