DragonFlyBSD

Also, let's pretend I didn't make a silly mistake.

The jz 1 and label 1: should become jz L1 and L1:

Jumping to the address 0x1 is silly.

On 05/25/2010 16:15, Venkatesh Srinivas (via DragonFly issue tracker) wrote:

Also, let's pretend I didn't make a silly mistake.
The jz 1 and label 1: should become jz L1 and L1:

Jumping to the address 0x1 is silly.

You can keep the label as 1: and use jz 1f instead (the f is for
'forward', as opposed to b, 'backward').

Cheers,
--
Thomas E. Spanjaard
tgen@netphreax.net
tgen@deepbone.net

Hi,

This is an improved version of the patch that corrects my silly jz mistake and
adds ffsl and flsl. It also implements both for x86_64. The x86-64 version is
branchless, using cmov.

This alternate snippet may be better and would allow for a branchless f?f(l) on
i386, except bsr and bsf are defined differently on Intel and AMD x86 machines.
It may be better on x86_64 than the cmov-based version:
xorl %eax, %eax
xorl %ecx, %ecx
bsrl 4(%esp), %eax
setnz %cl
addl %ecx, %eax
ret

Thanks,
-- vs

I just tested the i386 fls against its C equivalent on every input, to see that
it produces the same output; it passed. Running the C version, optimized by
gcc, took 49 sec on my hardware, the assembler version 10sec.

The x86_64 version is tested on a few test inputs, but not in the Dfly libc,
only as standalone .S files.

Correct a whilespace issue when patch is used.

x86_64 doesn't have DEFS.h.

:
:Venkatesh Srinivas <me@acm.jhu.edu> added the comment:
:
:x86_64 doesn't have DEFS.h.

Vekatesh, could you roll up all these patches and throw them into
    you git repo?  It's easier to bring them in and test them that way.

-Matt

Okay - its in my git tree on leaf, branch libc-asm.

-- vs

Resolved by commit 6cb1335d825070c7c4f5f0267d2b4c4b7dfd86be.