D - byte swapping ...
- Matthew Wilson (2/2) Sep 13 2003 Are there any built-in facilities for swapping the order of 16/32/64-bit
- Walter (4/6) Sep 13 2003 No. But you could write a function that uses inline asm and the BSWAP
- Matthew Wilson (12/18) Sep 13 2003 Well I just cobbled together
- Walter (8/18) Sep 14 2003 Yes. It does it in one instruction!
- Matthew Wilson (3/24) Sep 14 2003 Beautiful!
- Sean L. Palmer (39/49) Sep 14 2003 You have a bug there anyway. The last bit should be " | (i & 0xff000000...
- Matthew Wilson (10/47) Sep 14 2003 instruction,
- Philippe Mori (10/16) Sep 15 2003 But we would like to have intrinsic function for that since it would be
- Walter (10/18) Sep 15 2003 This might be a good idea.
- Serge K (3/5) Sep 15 2003 Then you can relax - VAX is dead, and AlphaAXP has support for VAX doubl...
- John Boucher (5/10) Sep 15 2003 Uh, I was just looking at the HP site and it seems that a new version of...
- Serge K (4/6) Sep 15 2003 all?
Are there any built-in facilities for swapping the order of 16/32/64-bit quantities?
Sep 13 2003
"Matthew Wilson" <matthew stlsoft.org> wrote in message news:bk0vkl$cgh$1 digitaldaemon.com...Are there any built-in facilities for swapping the order of 16/32/64-bit quantities?No. But you could write a function that uses inline asm and the BSWAP instruction.
Sep 13 2003
Well I just cobbled together
private uint swap(in uint i)
{
uint v_swap = (i & 0xff) << 24
| (i & 0xff00) << 8
| (i & 0xff0000) >> 8
| (i & 0xff000000) << 24;
return v_swap;
}
Will the inline asm version be substantially faster than this?
"Walter" <walter digitalmars.com> wrote in message
news:bk10dd$dj3$4 digitaldaemon.com...
"Matthew Wilson" <matthew stlsoft.org> wrote in message
news:bk0vkl$cgh$1 digitaldaemon.com...
Are there any built-in facilities for swapping the order of 16/32/64-bit
quantities?
No. But you could write a function that uses inline asm and the BSWAP
instruction.
Sep 13 2003
"Matthew Wilson" <matthew stlsoft.org> wrote in message
news:bk1214$fkj$1 digitaldaemon.com...
Well I just cobbled together
private uint swap(in uint i)
{
uint v_swap = (i & 0xff) << 24
| (i & 0xff00) << 8
| (i & 0xff0000) >> 8
| (i & 0xff000000) << 24;
return v_swap;
}
Will the inline asm version be substantially faster than this?
Yes. It does it in one instruction!
asm
{ naked;
bswap EAX ;
ret ;
}
Sep 14 2003
"Matthew Wilson" <matthew stlsoft.org> Beautiful! "Walter" <walter digitalmars.com> wrote in message news:bk16f2$mpo$2 digitaldaemon.com..."Matthew Wilson" <matthew stlsoft.org> wrote in message news:bk1214$fkj$1 digitaldaemon.com...Well I just cobbled together private uint swap(in uint i) { uint v_swap = (i & 0xff) << 24 | (i & 0xff00) << 8 | (i & 0xff0000) >> 8 | (i & 0xff000000) << 24; return v_swap; } Will the inline asm version be substantially faster than this?Yes. It does it in one instruction! asm { naked; bswap EAX ; ret ; }
Sep 14 2003
You have a bug there anyway. The last bit should be " | (i & 0xff000000) >>
24;"
This is the kind of thing you can easily make a template for... this should
go into the standard library.
template (class T)
{
void bswap(inout T i)
{
byte* p = cast(byte*)&i;
for (int b = 0; b < T.size/2; ++b)
instance swap(byte).swap(p[b], p[T.size-1-b]);
}
}
You can always specialize it for common types to use the bswap instruction,
and on platforms where byte access is slow you can probably find a way to
make it work only with words and shifts and masks.
Speaking of shifts and masks, I find that on many platforms it's better (and
it's never worse) to write the below like this instead, because it has to
load fewer mask constants:
uint v_swap = (i & 0xff) << 24
| (i & 0xff00) << 8
| (i >> 8) & 0xff00
| (i >> 24) & 0xff;
if your platform has ROL and ROR rotate shift instructions, since for ABCD,
you want DCBA:
ABCD ror 8 = DABC, has D and B in the right place
ABCD rol 8 = BCDA, has A and C in the right place
So
uint v_swap = rol(i & 0x00ff00ff, 8) | ror(i, 8) & 0x00ff00ff;
Since on any platform with word size of x bits, rol(uintx a, int bits) can
be done equivalently by (a << bits | a >> (x-bits))
and ror(uintx a, int bits) can be done equivalently by (a >> bits | a <<
(x-bits))
And many platforms have an instruction for this, I am not sure why low-level
languages like C do not have a rotate operator or at least a standard
intrinsic. __lrotl and __lrotr are not standard.
Sean
"Matthew Wilson" <matthew stlsoft.org> wrote in message
news:bk1214$fkj$1 digitaldaemon.com...
Well I just cobbled together
private uint swap(in uint i)
{
uint v_swap = (i & 0xff) << 24
| (i & 0xff00) << 8
| (i & 0xff0000) >> 8
| (i & 0xff000000) << 24;
return v_swap;
}
Will the inline asm version be substantially faster than this?
Sep 14 2003
You have a bug there anyway. The last bit should be " | (i & 0xff000000)Well spotted. I shall call you Eagle-eye Cherry. :)24;"This is the kind of thing you can easily make a template for... thisshouldgo into the standard library. template (class T) { void bswap(inout T i) { byte* p = cast(byte*)&i; for (int b = 0; b < T.size/2; ++b) instance swap(byte).swap(p[b], p[T.size-1-b]); } } You can always specialize it for common types to use the bswapinstruction,and on platforms where byte access is slow you can probably find a way to make it work only with words and shifts and masks.Would love to, but I can't bring myself to get D-templating until we've persuaded Walter of the merits of implicit instantiation. :(Speaking of shifts and masks, I find that on many platforms it's better(andit's never worse) to write the below like this instead, because it has to load fewer mask constants: uint v_swap = (i & 0xff) << 24 | (i & 0xff00) << 8 | (i >> 8) & 0xff00 | (i >> 24) & 0xff;Makes sense. I've used this form.if your platform has ROL and ROR rotate shift instructions, since forABCD,you want DCBA: ABCD ror 8 = DABC, has D and B in the right place ABCD rol 8 = BCDA, has A and C in the right place So uint v_swap = rol(i & 0x00ff00ff, 8) | ror(i, 8) & 0x00ff00ff; Since on any platform with word size of x bits, rol(uintx a, int bits) can be done equivalently by (a << bits | a >> (x-bits)) and ror(uintx a, int bits) can be done equivalently by (a >> bits | a << (x-bits)) And many platforms have an instruction for this, I am not sure whylow-levellanguages like C do not have a rotate operator or at least a standard intrinsic. __lrotl and __lrotr are not standard.Agreed. Let's see all these nitty-bitty things built into D.
Sep 14 2003
"Walter" <walter digitalmars.com> a écrit dans le message de news:bk10dd$dj3$4 digitaldaemon.com..."Matthew Wilson" <matthew stlsoft.org> wrote in message news:bk0vkl$cgh$1 digitaldaemon.com...But we would like to have intrinsic function for that since it would be portable and it would be more accessible to common programmers that may not have the knowledge on how to do it optimized... And it would also be nice to be able to discover if big or little endian is used on a given platform... Also conversions between different double format that exist on different platform might be interesting... since this would allows us to read binary files that where written on such platform.Are there any built-in facilities for swapping the order of 16/32/64-bit quantities?No. But you could write a function that uses inline asm and the BSWAP instruction.
Sep 15 2003
"Philippe Mori" <philippe_mori hotmail.com> wrote in message news:bk4eq6$218m$1 digitaldaemon.com...But we would like to have intrinsic function for that since it would be portable and it would be more accessible to common programmers that may not have the knowledge on how to do it optimized...This might be a good idea.And it would also be nice to be able to discover if big or little endian is used on a given platform...Already there as a predefined version: version (BigEndian) { ... } version (LittleEndian) { ... }Also conversions between different double format that exist on different platform might be interesting... since this would allows us to read binary files that where written on such platform.I'll worry about that when we've got a port to a cpu with different double formats!
Sep 15 2003
I'll worry about that when we've got a port to a cpu with different double formats!Then you can relax - VAX is dead, and AlphaAXP has support for VAX double format only for backward compatibility. Or should it be "had"? ..since Alpha is almost dead.
Sep 15 2003
In article <bk5slp$1mdi$1 digitaldaemon.com>, Serge K says...Uh, I was just looking at the HP site and it seems that a new version of OpenVMS is due out. (Yay!) Maybe a D compiler for it isn't such a bad idea after all? John Boucher The King had Humpty pushed.I'll worry about that when we've got a port to a cpu with different double formats!Then you can relax - VAX is dead, and AlphaAXP has support for VAX double format only for backward compatibility. Or should it be "had"? ..since Alpha is almost dead.
Sep 15 2003
Uh, I was just looking at the HP site and it seems that a new version ofOpenVMSis due out. (Yay!) Maybe a D compiler for it isn't such a bad idea afterall? Well, AFAIK C/C++ for Alpha does not support VAX double format anyhow. (maybe, Cobol does?;-)
Sep 15 2003