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July 23, 2015
drink 'n draw gouache-on-foam-on-pier

(retroactively posted Nov 2015)

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July 21, 2015
Music
broken beds
jerkiness


July 6, 2015
Music
check for weevils


July 3, 2015
Music
opening windows


July 2, 2015
drink 'n draw pencil

(retroactively posted Nov 2015)

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June 17, 2015
drink 'n monotype print

(retroactively posted Nov 2015)

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June 17, 2015
drink 'n monotype print

(retroactively posted Nov 2015)

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June 17, 2015
drink 'n monotype print

(retroactively posted Nov 2015)

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June 17, 2015
drink 'n monotype print

(retroactively posted Nov 2015)

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June 17, 2015
Music
long losta cola


June 2, 2015
Music
there went the block


May 25, 2015
Music
the new angle


May 12, 2015
Music
and so returns the heat


May 7, 2015
Music
they think you are special


May 4, 2015
Music
go away
more taint


May 1, 2015
Music
not seventy eight again


April 30, 2015
drink 'n stencil

(retroactively posted Nov 2015)

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April 30, 2015
Music
last chance for the apes


April 23, 2015
Music
an incoherent tooth


April 21, 2015
Music
in need of something


April 15, 2015
Music
smac reprise


April 13, 2015
Music
strong men also cry


April 10, 2015
Music
alternate form


April 3, 2015
Art dump - Feb 2015, pencil

(retroactively posted Nov 2015)

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April 2, 2015
Art dump - Feb 2015, pencil

(retroactively posted Nov 2015)

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April 1, 2015
Art dump - Jan 2015, pencil

(retroactively posted Nov 2015)



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April 1, 2015
Music
no fools flat


March 22, 2015
My new mp3 player!

This week's distraction is my new minimal HTML5 audio player, which is about 8kb of HTML/CSS/JS (or 3kb gzipped), and available here. The HTML5 audio tag does all of the work, this just does a basic AJAX-fetched media library, searching, and playlisting. I made it for all (1500 or so) of my recordings, but it should be pretty reusable...

Yes, no visualization, but that'd be so 1990s...

2 Comments


March 22, 2015
Music
not the odds


March 16, 2015
Music
all according to plan
imperial odds


March 12, 2015
Music
gotta have standards


March 10, 2015
Music
crumbling plaster


March 9, 2015
Music
meltage


March 7, 2015
Music
another day another toilet
fixing to leave


March 4, 2015
Music
lonely disappointed


February 23, 2015
Music
short fuse


February 19, 2015
Music
dark rooms
white tighty


February 16, 2015
Music
not having visions


February 12, 2015
Music
angles and snowflakes


February 4, 2015
Music
raccoon hunger


January 21, 2015
Music
slog


January 14, 2015
Music
alex_jason - 1 -- [9:04]
alex_jason - 2 -- [9:47]


December 14, 2014
Music
always more


December 6, 2014
Music
freeform jam with very and googleable and v


November 22, 2014
Music
a cold pillar


November 18, 2014
Music
bitter
kiss


November 6, 2014
Music
spheresofwet


November 4, 2014
EEL overkill



Comment...


October 29, 2014
Music
scheduling


October 28, 2014
my own private can of worms

First, from a recent 'git log' command:

    commit f94d5a07541a672b4446248409568c20bca9487d
    Author: Justin <justin@localhost>
    Date:   Sun Sep 11 21:52:27 2005 +0000
    
        Vss2Git
    
    diff --git a/jmde/mediaitem.h b/jmde/mediaitem.h*
    new file mode 100644
    index 0000000..52b8a8f
    --- /dev/null
    ++ b/jmde/mediaitem.h
    @@ -0,0 +1,37 @@
    #ifndef _MEDIAITEM_H_
    #define _MEDIAITEM_H_
    
    #include "pcmsrc.h"
    #include "../WDL/string.h"
    
    class MediaItem 
    {
    public:
      double m_position;
      double m_length;
    
      double m_startoffs;
      double m_fade_in_len, m_fade_out_len;
      int m_fade_in_shape, m_fade_out_shape;
    
      double m_volume, m_pan;
    
      WDL_String m_name;
    
      PCM_source *m_src;
    };
    
    class AudioChannel
    {
      WDL_PtrList<MediaItem> m_items;
      double m_volume, m_pan;
      bool m_mute, m_solo;
      WDL_String m_name;
      // recording source stuff, too
      // effect processor list
    
      // getsamples type interface
    };
    
    
    #endif
    
    * Trivia: guess what jmde (JMDE) stands for?
..and to think, back when we used VSS we didn't even have commit messages! Soon after, "AudioChannel" became instantiable and went on to be known as "MediaTrack", and as one would hope many other things ended up changing.

Wow, 9 years have gone by.

I've been having a blast this week working on something that let me make this:

The interesting bit of this is not the contents of the video itself -- 3 hasty first-takes with drums, bass, and guitar, each with 2 cameras (a Canon 6D and a Contour Roam 2) -- but how it was put together.

I've spent much of the last week experimenting with improving the video features of REAPER, specifically adding support for fades and video processing. This is a ridiculously large can of worms to open, so I'm keeping it mostly contained in my office and studio.

Working on video features is reminding me of when I was first starting work on what would become REAPER: I was focused on doing things that I could use then and there for things I wanted to make. It is incredibly satisfying to work this way. So now, I'm doing it in a branch (thank you git), as it is useful for me, but so incredibly far from the usability standard that REAPER represents now (even if you argue that REAPER is poorly designed, it's still 100x better than what I've done this week). You can't go put half-baked, poor performing, completely-programmer-oriented video features into a 9 year old program.

Here is a .gif showing how the video filters work -- the syntax has since been simplified a bit, but basically you have meta-video items which can combine other video items on the fly. So you can write new transitions or customize existing transitions while you work (which is something I love about JSFX).

I'm going to keep working on this, it might get there someday. Former Vegas fans, fear not, REAPER isn't going to become a video editor. I'm just going for a taste...

6 Comments


October 27, 2014
Music
transitioning time


October 21, 2014
Music
light and heat


October 18, 2014
Music
oh no itsa g


October 10, 2014
Music
a quick woodland waltz
open windows falling apart
post waltz
yossy says


October 6, 2014
Music
possum pocket


October 2, 2014
Music
back are we and


August 29, 2014
Music
something newer
something over


August 26, 2014
Music
boots
damp with envy


August 20, 2014
Music
nude brick


August 19, 2014
Music
sundays are far away


August 13, 2014
Music
hookworms


July 24, 2014
licecap 1.25beta 3

I just posted (to our prerelease site) LICEcap 1.25 beta 3, which includes support for using transparency for smaller images. I had some fun debugging this (including some very stupid mistakes on my part that took about an entire day to debug, oops).

I also had some fun writing logic to decide what to do when a pixel could be encoded as transparent, but also could be well-represented by an indexed color. Iniitially I had it only use the indexed value if the previous pixel was indexed, but it ended up being quite a bit better to do track the occurence of transparent pixels and pixels of that index, and use the one that is more common. There is probably a better algorithm to use here, but that saw some good gains. For comparison, I ran 1.24 and 1.25 beta 3 at the same time for a stupid demo video. The 1.24 version was 2.5MB, the 1.25 beta 3 version was 1.5MB. WIN. It ultimately is highly dependent on the content, though, so I might look at trying some other things out...



1 Comment


July 15, 2014
checking assumptions

Very often in computer code integers are divided by powers of two, such as 2, 4, 8, 16, 32, 64, and so on). These divisions are much faster than dividing by other numbers (since computers represent the underlying number in binary). In C/C++, there are two ways this type of division is typically expressed: normal division (x/256), or a shift (x<<8). These two methods produce the same results for non-negative values, and depending on the meaning of the code in question, (x/256) is often more readable, and thus I use it regularly.

If x is signed and is negative, division rounds towards 0, whereas the shift rounds towards negative infinity, but in situations where rounding of negative values is not important, I had generally assumed that modern compilers would generate similarly efficient code (reducing x/256 into a single x86 sar instruction).

It turns out, testing with a two modern compilers (and one slightly out of date compiler), this is not the case.

Here is the C code:

  void b(int r);
  void f(int v)
  {
    int i;
    for (i=0;i<v/256;i++) b(v > 0 ? v/65536 : 0);
  }

  void f2(int v)
  {
    int i;
    for (i=0;i<(v>>8);i++) b(v > 0 ? v >> 16 : 0);
  }

Ideally, a compiler should generate identical code for each of these functions. In the case of the loop counter, if v is less than 0, how it is rounded makes no difference. In the case of the parameter to b(), the code v >> 16 is only evaluated if v is known to be above 0.

Let's look at the output of some compilers (removing decoration and unrelated code). I've marked some code as bold to signify instructions that could be eliminated (with slight changes to the surrounding instructions):

  • Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
    Xcode 5.1.1 on OSX 10.9.4
    Target: x86_64-apple-darwin13.3.0
    Command line flags: -O2 -fomit-frame-pointer

    f():                              # using divides
    	cmpl	$256, %edi
    	jl	LBB0_3            # if v is less than 256, skip loop
    
            # v is known to be 256 or greater. 
    
    	movl	%edi, %ebx
    	sarl	$31, %ebx         # ebx=0xffffffff if negative, 0 if non-negative
    	movl	%ebx, %r14d    
    	shrl	$24, %r14d        # r14d=0xff if negative, 0 if non-negative
    	addl	%edi, %r14d       # r14d = (v+255) if v negative, v if v non-negative
    	sarl	$8, %r14d         # r14d = v/256
    
    	shrl	$16, %ebx         # this will make ebx 65535 if v negative, 0 if v non-negative
    	addl	%edi, %ebx        # ebx = (v+65535) if v negative, v if v non-negative
    	sarl	$16, %ebx         # ebx = v/65536
    
            # interestingly, the optimizer used its knowledge of v being greater than 0 to remove the ternary conditional expression completely.
    
    	xorl	%ebp, %ebp
    LBB0_2:
    	movl	%ebx, %edi
    	callq	_b
    	incl	%ebp
    	cmpl	%r14d, %ebp
    	jl	LBB0_2
    LBB0_3:
    
    
    
    f2():                             # using shifts
    	movl	%edi, %ebp
    	sarl	$8, %ebp          # ebp = v>>8
    	testl	%ebp, %ebp
    	jle	LBB1_3            # if less than or equal to 0, skip
    
    	movl	%edi, %eax
    	sarl	$16, %eax         # eax = v>>16
    	xorl	%ebx, %ebx
    	testl	%edi, %edi
    	cmovgl	%eax, %ebx        # if v is greater than 0, set ebx to eax
    
            # the optimizer could also have removed the xorl/testl/cmovgl sequence as well
    
    LBB1_2:
    	movl	%ebx, %edi
    	callq	_b
    	decl	%ebp
    	jne	LBB1_2
    LBB1_3:
    
    
    In the first function (division), the LLVM optimizer appears to have removed the ternary expression (checking to see if v was greater than 0), likely because it knew that if the loop was running, v was greater than 0. Unfortunately, it didn't apply this knowledge to the integer divisions of v, which would have allowed it to not generate (substantial) rounding code.

    In the second function (shifts), LLVM wasn't required to generate rounding code (as C's >> maps to x86 sar directly), but it also didn't use the knowledge that v would be greater than 0.

  • Microsoft (R) C/C++ Optimizing Compiler Version 18.00.30501 for x64
    Visual Studio Express 2013 for Windows Desktop on Windows 7
    Command line flags: /O2 (/Os produced different results, but nothing related to rounding)
    
    f():                              # using divides
    
            mov     eax, ecx
            mov     ebx, ecx
            cdq                       # set edx to 0xffffffff if v negative, 0 otherwise
            movzx   edx, dl           # set edx to 0xff if v negative, 0 otherwise
            add     eax, edx          # eax = v+255 if v negative, v otherwise
            sar     eax, 8            # eax = v/256
            test    eax, eax
            jle     SHORT $LN1@f      # skip loop if v/256 is less than or equal to 0
            mov     QWORD PTR [rsp+48], rdi
    
            mov     edi, eax          # edi is loop counter
    $LL3@f:
            test    ebx, ebx
            jle     SHORT $LN6@f      # if v is less than or equal to 0, jump to set eax to 0
            mov     eax, ebx
            cdq                       # set edx to 0xffffffff if v negative, 0 otherwise
            movzx   edx, dx           # set edx to 0xffff if v negative, 0 otherwise
            add     eax, edx          # eax = v+65535 if v negative, v otherwise
            sar     eax, 16           # eax = v/65536
            jmp     SHORT $LN7@f
    $LN6@f:
            xor     eax, eax
    $LN7@f:
            mov     ecx, eax
            call    b
            dec     rdi
            jne     SHORT $LL3@f
    
            mov     rdi, QWORD PTR [rsp+48]
    $LN1@f:
    
    f2():                             # using shifts
            mov     eax, ecx
            mov     ebx, ecx
            sar     eax, 8            # eax = v>>8
            test    eax, eax
            jle     SHORT $LN1@f2     # skip loop if v>>8 is less than or equal to 0
    
            mov     QWORD PTR [rsp+48], rdi
            mov     edi, eax
    $LL3@f2:
            test    ebx, ebx
            jle     SHORT $LN6@f2     # if v is less than or equal to 0, jump to set ecx to 0
            mov     ecx, ebx
            sar     ecx, 16           # ecx = v>>16
            jmp     SHORT $LN7@f2
    $LN6@f2:
            xor     ecx, ecx
    $LN7@f2:
            call    b
            dec     rdi
            jne     SHORT $LL3@f2
            mov     rdi, QWORD PTR [rsp+48]
    $LN1@f2:
    
    
    VS 2013 generates different rounding code for the division, using cdq/movzx (or cdq/and if shifting by something other than 8 or 16 bits).

    Also worth noting is that VS 2013 doesn't even bother moving the invariant ternary operator and (v/65536) or (v>>16) out of the loop. Ideally, it could move that calculation out of the loop, or remove the ternary operator completely. Ouch. I have to say, VS 2013 does seem to produce pretty good code overall, but I guess most of ours is heavily in floating point these days.

  • gcc 4.4.5
    Linux x86_64
    Command line flags: -O2 -fomit-frame-pointer

    f():                              # using divides
            testl   %edi, %edi
            movl    %edi, %ebp        # ebp = edi = v
            leal    255(%rbp), %r12d  # r12d = v+255
    
            cmovns  %edi, %r12d       # set r12d to v, if v is non-negative (otherwise r12d was v+255)
            sarl    $8, %r12d         # r12d = v/256
            testl   %r12d, %r12d
            jle     .L14              # if r12d is less than or equal to 0, skip
            movl    %edi, %r14d
            xorl    %ebx, %ebx        # ebx is loop counter
            xorl    %r13d, %r13d
            sarl    $16, %r14d        # r14d = v>>16
    .L13:
            testl   %ebp, %ebp
            movl    %r13d, %edi
            cmovg   %r14d, %edi       # if v is greater than 0, use v>>16 instead of 0
            addl    $1, %ebx
            call    b
            cmpl    %r12d, %ebx
            jl      .L13
    .L14:
    
    f2():                             # using shifts
            movl    %edi, %r12d
            sarl    $8, %r12d
            testl   %r12d, %r12d
            movl    %edi, %ebp
            jle     .L6               # skip loop if (v>>8) is less than or equal to 0
            movl    %edi, %r14d
            xorl    %ebx, %ebx        # ebx is loop counter
            xorl    %r13d, %r13d
            sarl    $16, %r14d        # r14d = (v>>16)
    .L5:
            testl   %ebp, %ebp
            movl    %r13d, %edi
            cmovg   %r14d, %edi       # if v is greater than 0, use v>>16 instead of 0
            addl    $1, %ebx
            call    b
            cmpl    %r12d, %ebx
            jl      .L5
    .L6:
    
    
    
    gcc 4.4 does an interesting job, using lea to generate v+255, and then cmovns to replace it with v if v is non-negative. It doesn't bother generating rounding code for v/65536, but it does still generate rounding code for v/256, even though any non-positive result for v/256 is treated the same way throughout. Also, gcc doesn't eliminate the non-varying ternary expression, nor put the constant v/65536 or v>>16 outside of the loop.

Conclusions?

I'm not sure what to say here -- modern compilers can generate a lot of really good code, especially looking at floating point and SSE, but this makes me feel as though some of the basics have been neglected. If I were a better programmer I'd go dig into LLVM and GCC and submit patches.

I should have also tested ICC, but I've spent enough time on this, and the only ICC version we use is old enough that I would just regret not using the latest.

For comparison, here is what I would like to see LLVM generate for f():


f():                              # using divides
	cmpl	$256, %edi
	jl	LBB0_3            # if v is less than 256, skip loop

	movl	%edi, %ebx
	movl	%edi, %ebp
	shrl	$8, %ebx          # ebx = v/256, since v is non-negative
	shrl	$16, %ebp         # ebp = v/65536, since v is non-negative

LBB0_2:
	movl	%ebp, %edi
	callq	_b
	decl    %ebx
	jnz	LBB0_2
LBB0_3:

Performance-wise, I'm sure they wouldn't differ in any meaningful way, but the decrease in size would be nice.

Finally: write for the compiler you have, not the compiler you wish you had. When performance is important, use shifts instead of divides, or use unsigned types (which really should generate the same code for (x/256) vs (x>>8)). Move as much logic out of the loop as you can -- yes, the compiler might be able to do it for you, but why depend on that? But most important of all: test your assumptions.

5 Comments


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