Path: csiph.com!weretis.net!feeder9.news.weretis.net!i2pn.org!i2pn2.org!.POSTED!not-for-mail
From: dxf <dxforth@gmail.com>
Newsgroups: comp.lang.forth
Subject: Re: Parsing timestamps?
Date: Thu, 10 Jul 2025 21:09:21 +1000
Organization: i2pn2 (i2pn.org)
Message-ID: <a5b34bd3fc76ab03acc40d48dc9bfd4bf65ebbdd@i2pn2.org>
References: <1f433fabcb4d053d16cbc098dedc6c370608ac01@i2pn2.org> <300ba9a1581bea9a01ab85d5d361e6eaeedbf23a@i2pn2.org> <nnd$619ca290$2bff25f3@fa4b7a265c28888c> <4d440297d7e17251ebc50774bacfec73e184f9bc@i2pn2.org> <2025Jul5.104922@mips.complang.tuwien.ac.at> <6fd9f665e73ad93270fff88eca894ba69424cac7@i2pn2.org> <87a55dxbft.fsf@nightsong.com> <7f461d46127d3628c600f3df0794899bdaa5ff04@i2pn2.org> <87tt3kwtmf.fsf@nightsong.com> <74805b78ed72545f2e12c9b6985726c3dad5ae2a@i2pn2.org> <2025Jul10.103549@mips.complang.tuwien.ac.at>
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Injection-Date: Thu, 10 Jul 2025 11:09:23 -0000 (UTC)
Injection-Info: i2pn2.org; logging-data="4176544"; mail-complaints-to="usenet@i2pn2.org"; posting-account="XPw7UV90Iy7EOhY4YuUXhpdoEf5Vz7K+BsxA/Cx8bVc";
User-Agent: Mozilla Thunderbird
In-Reply-To: <2025Jul10.103549@mips.complang.tuwien.ac.at>
Content-Language: en-GB
X-Spam-Checker-Version: SpamAssassin 4.0.0
Xref: csiph.com comp.lang.forth:134010

On 10/07/2025 6:35 pm, Anton Ertl wrote:
> dxf <dxforth@gmail.com> writes:
>> The catch with SSE is there's nothing like FCHS or FABS
>> so depending on how one implements them, results vary across implementations.
> 
> You can see in Gforth how to implement FNEGATE and FABS with SSE2:
> 
> see fnegate 
> Code fnegate  
>    0x000055e6a78a8274:   add    $0x8,%rbx
>    0x000055e6a78a8278:   xorpd  0x24d8f(%rip),%xmm15        # 0x55e6a78cd010
>    0x000055e6a78a8281:   mov    %r15,%r9
>    0x000055e6a78a8284:   mov    (%rbx),%rax
>    0x000055e6a78a8287:   jmp    *%rax
> end-code
>  ok
> 0x55e6a78cd010 16 dump 
> 55E6A78CD010: 00 00 00 00  00 00 00 80 - 00 00 00 00  00 00 00 00 
>  ok
> see fabs 
> Code fabs  
>    0x000055e6a78a84fe:   add    $0x8,%rbx
>    0x000055e6a78a8502:   andpd  0x24b15(%rip),%xmm15        # 0x55e6a78cd020
>    0x000055e6a78a850b:   mov    %r15,%r9
>    0x000055e6a78a850e:   mov    (%rbx),%rax
>    0x000055e6a78a8511:   jmp    *%rax
> end-code
>  ok
> 0x55e6a78cd020 16 dump 
> 55E6A78CD020: FF FF FF FF  FF FF FF 7F - 00 00 00 00  00 00 00 00 
> 
> The actual implementation is the xorpd instruction for FNEGATE, and in
> the andpd instruction for FABS.  The memory locations contain masks:
> for FNEGATE only the sign bit is set, for FABS everything but the sign
> bit is set.
> 
> Sure you can implement FNEGATE and FABS in more complicated ways, but
> you can also implement them in more complicated ways if you use the
> 387 instruction set.  Here's an example of more complicated
> implementations:
> 
> see fnegate 
> FNEGATE 
> ( 004C4010    4833C0 )                XOR     RAX, RAX
> ( 004C4013    F34D0F7EC8 )            MOVQ    XMM9, XMM8
> ( 004C4018    664C0F6EC0 )            MOVQ    XMM8, RAX
> ( 004C401D    F2450F5CC1 )            SUBSD   XMM8, XMM9
> ( 004C4022    C3 )                    RET/NEXT
> ( 19 bytes, 5 instructions )
>  ok
> see fabs 
> FABS 
> ( 004C40B0    E8FBEFFFFF )            CALL    004C30B0  FS@
> ( 004C40B5    4885DB )                TEST    RBX, RBX
> ( 004C40B8    488B5D00 )              MOV     RBX, [RBP]
> ( 004C40BC    488D6D08 )              LEA     RBP, [RBP+08]
> ( 004C40C0    0F8D05000000 )          JNL/GE  004C40CB
> ( 004C40C6    E845FFFFFF )            CALL    004C4010  FNEGATE
> ( 004C40CB    C3 )                    RET/NEXT
> ( 28 bytes, 7 instructions )

The latter were basically what was existed in the implementation.  As they
don't handle -ve zero (or NANs) I swapped them out for the former ones you
mention.