Re: [ros-dev] [ros-diffs] [greatlrd] 23826: Wrote RtlUshotByteSwap RtlUlongByteSwap and RtlUlonglongByteSwap to asm code. but we need a C api for header to linking it right. Put the asm version to i386

[Timo Kreuzer]

If it should be optimized, inlined asm should be used as following:

Reuel ben Yisrael schrieb:
> >   +.globl
> > _UlongByteSwap
> >  + 
> >  +.intel_syntax noprefix
> >  +
> >  +/* FUNCTIONS ***************************************************************/
> >  +
> >  +_UlongByteSwap:
> >  +                       push  ebp          // save base 
> >  +                       mov   ebp,esp      // move stack to base
> >  +                       mov   eax,[ebp+8]  // load the ULONG                       
> >  +                       bswap eax          // swap the ULONG
> >  +                       pop   ebp          // restore the base   
> >  +                       ret
> >   
> >
> >       
>  this should work:
>
>  _UlongByteSwap:
>                         mov   eax,[esp+8]  // load the ULONG                       
>                         bswap eax          // swap the ULONG
>                         ret
>     
static force_inline ULONG UlongByteSwap(ULONG x)
{
    asm volatile(
        "bswap %0;"
        : "=r" (x)
        : "0" (x)
    );
    return x;
}


> >   +.globl
> > _UlonglongByteSwap
> >  + 
> >  +.intel_syntax noprefix
> >  +
> >  +/* FUNCTIONS ***************************************************************/
> >  +
> >  +_UlonglongByteSwap:
> >  +                       push  ebp          // save base 
> >  +                       mov   ebp,esp      // move stack to base
> >  +                       mov   edx,[ebp+8]  // load the higher part of ULONGLONG
> >  +                       mov   eax,[ebp+12] // load the lower part of ULONGLONG    
> >  +                       bswap edx          // swap the higher part
> >  +                       bswap eax          // swap the lower part 
> >  +                       pop   ebp          // restore the base   
> >  +                       ret
> >   
> >
> >       
>  _UlonglongByteSwap:
>                         mov   edx,[esp+8]  // load the higher part of ULONGLONG
>                         mov   eax,[esp+12] // load the lower part of ULONGLONG    
>                         bswap edx          // swap the higher part
>                         bswap eax          // swap the lower part 
>                         ret
>     
static force_inline ULONGLONG UlonglongByteSwap(ULONGLONG x)
{
    ULONG h,l;

    asm volatile ("": "=d" (l), "=a" (h): "A"
(x));

    asm volatile (
        "bswap %%eax;"
        "bswap %%edx;"
        : "=A" (x)
        : "d" (l), "a" (h)
    );
    return x;
}
>     
> >   +_UshortByteSwap:
> >  +                       push  ebp          // save base 
> >  +                       mov   ebp,esp      // move stack to base
> >  +                       mov   eax,[ebp+8]  // load the USHORT                       
> >  +                       bswap eax          // swap the USHORT, xchg is slow so we use
> > bswap with rol 
> >  +                       rol   eax,16       // make it USHORT
> >  +                       pop   ebp          // restore the base   
> >  +                       ret
> >   
> >
> >       
>  _UshortByteSwap:
>                         mov   eax,[esp+8]  // load the USHORT                       
>                         bswap eax          // swap the USHORT, xchg is slow so we use
> bswap with rol 
>                         rol   eax,16       // make it USHORT
>                         ret
>
>
>  or to save a byte...
>
>  _UshortByteSwap:
>                         mov   ebx,[esp+8]  // load the USHORT                       
>                         mov   al, bh
>                         mov   ah, bl
>                         ret
>     
static force_inline USHORT UshortByteSwap(USHORT x)
{
    asm volatile(
        "rolw $8, %0;"
        : "=r" (x)
        : "0" (x)
    );
    return x;
}