Re: Re : [linux-audio-dev] Float to int conversions

New Message Reply About this list Date view Thread view Subject view Author view Other groups

Subject: Re: Re : [linux-audio-dev] Float to int conversions
From: Erik de Castro Lopo (erikd_AT_mega-nerd.com)
Date: Fri Nov 02 2001 - 10:30:37 EET

It really blew my mind when "Letz Stephane" <letz_AT_rd.grame.fr> said:

> I made some tests on a G3 with Code Warrior 5 with optimizations on (Mac OS
> 8.6). The lrint/lrintf is slower that the standard cast code.

Hmm, thats very interesting. Maybe we can take this off line and work on
a solution. Interested?

> Here are the result of disassembing 2 tests functions :
>
>
> int test1 (float in){ return lrintf(in); } gives :
>
> ...
> 00000000: 7C0802A6 mflr r0
> 00000004: 90010008 stw r0,8(SP)
> 00000008: 9421FFC0 stwu SP,-64(SP)
> 0000000C: 48000001 bl .rinttol
> 00000010: 60000000 nop
> 00000014: 80010048 lwz r0,72(SP)
> 00000018: 38210040 addi SP,SP,64
> 0000001C: 7C0803A6 mtlr r0
> 00000020: 4E800020 blr
> ...
>
> Is seems that lrint/lrintf are implemented in the MathLib using the rinttol
> call.

On linux, this is an inline function while on Mac its a function call. Maybe we can
do better. I am far from beting a PPC assembler expert (in fact I've never looked
at it) but I understand that PPC has at least two float to int conversion functions;
one for truncation and one for rounding. Is that correct?

If this is the case, then maybe we can use and inline function with assembler in
it.

Erik 

-- 
+-----------------------------------------------------------+
  Erik de Castro Lopo  nospam_AT_mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
"It is grossly irresponsible to connect a Windows machine directly to 
the net.  ;-)"  -- John Wiltshire on the Sydney Linux User Group mailing list

New Message Reply About this list Date view Thread view Subject view Author view Other groups

This archive was generated by hypermail 2b28 : Fri Nov 02 2001 - 10:26:28 EET