Low Level Programming and Computer Architecture - Lecture 5 · Low Level Programming and Computer Architecture Lecture 5 ... difference between knowing the ... Low Level Programming

Low Level Programming and Computer ArchitectureLecture 5

Carl Henrik Ek{chek}@csc.kth.se

Royal Institute of Technology

March 10, 2013

Ek KTH

Low Level Programming and Computer Architecture

Last Lecture• Abstraction• File formats• Structured Data

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Abstraction of Data

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Abstraction of Data

Representing Images• Indexed Images• Truecolour• HAM - Hold And Modify

• Image sizeI 640× 480× 3 =

921600bytes = 900KB

• PBM, PGM, PPM, PNM, BMP• executable

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http://paulbourke.net/dataformats/ppm/

http://paulbourke.net/dataformats/bmp/

https://developer.apple.com/library/mac/#documentation/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html

Compression

Defintion

f : X → Yg : Y → X

• RAW - uncompressed data• Lossless

I x = g (f (x))• Lossy

I d(x,g (f (x))) 6= 0I What is d(·, ·)

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Compression: Lossless

Lossless• Run-length encoding• Frequency dependency

I Huffman encoding

• LHA, LZX, ZIP, TAR,GZIP, . . .

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Huffman encoding• David A. Huffman, 1952

MIT• Entropy encoding• Claude Shannon

I Father of Information theory

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http://en.wikipedia.org/wiki/David_A._Huffman

http://en.wikipedia.org/wiki/Claude_Shannon


Dictionary Coding• Dictionary• LZW• Original Unix compress

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Compression: Lossy

Images• Lots of different formats• Lossless

I TIFF, GIF, BMP

• LossyI JPEG

• Loss function

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Compression: Lossy

JPEGa

aWikipedia

• Change-of-Basis

f (t) =∫ ∞−∞

f (x)e−2πixtdx

• perception• what is the loss function?

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http://upload.wikimedia.org/wikipedia/commons/7/72/Fourier_transform_time_and_frequency_domains_%28small%29.gif

This Lecture• Abstraction

I Left-overs from last time

• Programming• Structured Data

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Communication

Parity• Check Bit• Even/Odd

I number of set bits needs to beEven/Odd

I Parity bit compensates

• Checksum: CRC• ASCII, TCP/IP traffic

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Communication





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Communication





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Communication

Error Correcting Codes• Detect error• Correct• Distance between codes

Copyright © 2012 Pearson Education, Inc. 0-0

Figure 1.29 An error-correcting code

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Communication


Figure 1.30 Decoding the pattern 010100using the code in Figure 1.30

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Recapitulation

Program Execution• Code is just data• OS Loads executable

I Lecture 7 May 3rd

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Recapitulation

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Recapitulation

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Recapitulation

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Disassembly• Machine Code and Assembler• Recover Code from

executable• Intel

• Motorla 68k

• AMD Reference Manual

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http://www.intel.com/content/www/us/en/processors/architectures-software-developer-manuals.html

http://www.freescale.com/files/archives/doc/ref_manual/M68000PRM.pdf

http://support.amd.com/us/Processor_TechDocs/24594_APM_v3.pdf

Executable

Executable• Mac

I Mach-OI machine.h

• PE - Windows, ELF - Linux• Extended Hunk Format -

AmigaOS• Library

I Static, Dynamic

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https://developer.apple.com/library/mac/#documentation/DeveloperTools/Conceptual/MachORuntime/Reference/reference.html

http://www.opensource.apple.com/source/cctools/cctools-836/include/mach/machine.h

Abstraction II

Programming Languages• Generate Instructions• Levels of abstraction• “Generations”

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Abstraction II

Second Generation• Assembly• Mnemonics• Injective mapping

(one-to-one)• Assembler

19/3/13 10:16 Parallel byte-wise maximum

Page 1 of 3http://ada.untergrund.net/forum/index.php?action=vthread&forum=4&topic=870

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Amiga Demoscene Archive Forum / Coding / Parallel byte-wise maximum

Author Message

BlueberryForums Member

#1 - Posted: 25 Feb 2013 10:04 - Edited by: BlueberryReply Quote

Hi!

It has been discussed in here a couple of times how to do byte-wise saturated add one longword at a time.

But how about byte-wise maximum? If we have byte values up to 127 in all four bytes of D0 and D1, we can perform abyte-wise maximum like this:

move.l #$80808080,d2 sub.l d1,d0 ; byte-wise differences with overflows add.l d2,d0 ; overflows negated, msb of each byte is 1 iff difference is positive and.l d0,d2 ; 128 for bytes where difference is positive, 0 for the others move.l d2,d3 lsr.l #7,d3 sub.l d3,d2 ; 127 for bytes where difference is positive, 0 for the others and.l d2,d0 ; only positive differences add.l d1,d0 ; original + positive differences = maximum

With appropriate pairing, these 9 instructions result in an overhead (compared to simply using one of the sources) of1.125 cycles per byte. One of the sources (D1) can be in memory for no extra cost.

Can it be done better? Can we get down to 1 cycle? :)

Suppose we need, say, 6 bits of precision on our byte values, but those 6 bits have to be placed in the upper bits of eachbyte (in the memory operand and the destination). We can do this by a move (from memory) and an lsr #1 at thebeginning and an lsl #1 at the end, resulting in 3 more instructions (1.5 cycles per byte total). Is there perhaps somebetter way to do it?

jamie2010Forums Member

#2 - Posted: 25 Feb 2013 14:14Reply Quote

Hey,

Do you need to do this sort of operation several times by pixel?

jamie2010Forums Member


By Pixels i mean for 4 pixels.

daltonForums Member


I can't think of a quicker way to perform this operation. What bothers me is that so many cycles are spent on creating abit mask from the sign bits (x-x>>7). Another way of doing it would be (x>>7)*127. It saves one line of code and oneregister. But I don't think it's any faster =(

move.l #$80808080,d2 sub.l d1,d0 ; byte-wise differences with overflows add.l d2,d0 ; overflows negated, msb of each byte is 1 iff difference is positive and.l d0,d2 ; 128 for bytes where difference is positive, 0 for the others

Ek KTH


Abstraction II

Third Generation• Higher-level

I not injective

• Machine independent• Compiled/Interpreted

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Paradigms

Imperative• Traditional algorithm• Define procedure• State changes• Machine Language, Pascal,C, C++, Python

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Paradigms

Functional• Express as functional evaluation• Recursion• Avoid state changes• Haskell, Lisp

• Beautiful but slowI academic

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Paradigms

Declarative• Defines logic• Does not define flow• SQL, Prolog

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Figure 6.2 The evolution ofprogramming paradigms

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Types

Compiled• Translates whole program• Executes program• Intermediate stages

I ParserI Compile timeI Run time

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Types

Interpreted• Translates and executes• Matlab

• Fast development• Hard to Optimise

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Types

Typing• Metadata• Strongly Typed

I JAVA, Python, C++

• Weakly TypedI C

• UntypedI Assembler

• Static, Dynamic

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Virtual Machine• Abstraction of Hardware• Hard to make efficient• Convinient distribution• API

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Feynman

“You can know the name of abird in all the languages of theworld, but when you’re finished,you’ll know absolutely nothingwhatever about the bird... Solet’s look at the bird and seewhat it’s doing– that’s whatcounts. I learned very early thedifference between knowing thename of something and knowingsomething.”

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Summary• Imperative• Compiled/Interpreted• Virtual Machine

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Misc

Turing Completness• Simluate Turing Machine

I States, memory, aritmetic

• All Imperative languages• SQL, HTML

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Misc

Esoteric Languages• Brainfuck

I Only uses > < + { . , []

I code

• MalbolgeI Eight circle of HellI code

• ShakespeareI code

• Esolang

• IOCCC

Ek KTH


http://esolangs.org/wiki/Hello_world_program_in_esoteric_languages#Brainfuck

http://en.wikipedia.org/wiki/Malbolge#.22Hello_World.21.22_in_Malbolge

http://shakespearelang.sourceforge.net/report/shakespeare/shakespeare.html#sec:hello

http://esolangs.org/wiki/Main_Page

http://www.ioccc.org

Next Lecture• April 23th• C Programming• Practical Session April 17th

Ek KTH


e.o.f.

Ek KTH


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Low Level Programming and Computer Architecture - Lecture 5 · Low Level Programming and Computer Architecture Lecture 5 ... difference between knowing the ... Low Level Programming