Komap's Blog

convert 16 bit “half float” to 32 bit float

komap — Thu, 01 Dec 2011 17:22:04 +0000

float convert16to32float(unsigned int Xi_Value)
{ 
 //TODO:test, imporve, optimize..
  int exp = (Xi_Value>>10) & 0x01f;
  float g=0;
  unsigned int *i=(unsigned int *) & g;
  Xi_Value &= 0xffff;
  *i=0;
  *i |= Xi_Value << 16 & 0x80000000; //sign
  *i |= (exp-15+127) << 23; //exponent 
  *i |= (Xi_Value & 0x3FF) << 13; //value
  return g;
}

copy DB from MS SQL to MYSQL

komap — Thu, 21 Jul 2011 15:33:02 +0000

I’ve burned too much on this simple task, so I want to keep some gotchas it here.
The task: copy DB from MS SQL to MYSQL.

Tools

MySQL migrate — I couldn’t make it work.
http://www.convert-in.com/ — seem to be OK, but demo version is limited, so I’m not sure. Full version – $50.
bcp – command line tool; it was extremely difficult (yet possible) to export to a file that MySQL can eat.

Code


dbcDataAdapter l_SourceDA = new OdbcDataAdapter(l_QuerySource, m_strSource);
        OdbcDataAdapter l_TargetDA = new OdbcDataAdapter(l_QueryTarget, m_strTarget);
        OdbcCommandBuilder cmb = new OdbcCommandBuilder(l_TargetDA); //mandatory! Even if I don't use cmb, this line is crucial as in creates INSERT command
        string l_TableName = cmb.QuoteIdentifier(Xi_TableName, m_cTarget);

        DataSet l_SourceDS = new DataSet();
        DataSet l_TargetDS = new DataSet();
        int l_Rows = l_SourceDA.Fill(l_SourceDS, Xi_TableName);
        if (l_Rows <= 0)
        {
          Log("Empty table");
          return;
        }
        l_TargetDA.Fill(l_TargetDS, l_TableName);

        DataTable l_tblSource = l_SourceDS.Tables[Xi_TableName];
        DataTable l_tblTarget = l_TargetDS.Tables[l_TableName];

        int l_Errors = 0;
        // Loop through the top five rows, and write the first column to the screen.
        foreach (DataRow l_r in l_tblSource.Rows)
        {
          try
          {
            l_tblTarget.ImportRow(l_r);
            l_tblTarget.Rows[l_tblTarget.Rows.Count - 1].SetAdded();
          }
          catch (OdbcException ex)
          {
            Log(ex.Message);
            l_Errors++;
          }
        }
        Log(string.Format("table {0}: {1} errors out of {2} records",
          Xi_TableName, l_Errors, l_Rows));
        DataSet l_Changed = l_TargetDS.GetChanges();
        tblTarget.Update(l_Changed);

This is OK; but I needed support for tables with dash (“-”).
This was much harder; this thread was useful.
So two changes that fix it:

   //create command
    OdbcCommand cmdInsert = cmb.GetInsertCommand();
        cmdInsert.CommandText = cmdInsert.CommandText.ToLower().Replace(Xi_TableName.ToLower(), "`" + Xi_TableName + "`"); 
//MSSQL use "[" and "]"; there are prefix/postfix fields somehere in the data adapter
     ...

//instead of just updating target data set:
 OdbcDataAdapter l_NewTargetDA = new OdbcDataAdapter(l_TargetDA.SelectCommand);
        l_NewTargetDA.TableMappings.Add("Table", l_TableName);
        l_NewTargetDA.InsertCommand = cmdInsert;
        l_NewTargetDA.Update(l_Changed);

Hopefully this will be useful for someone.

One more HLSL trick

komap — Thu, 07 Jul 2011 17:34:08 +0000

When implementing a quite complex pixel shader on pixel shader for multi-cascade shadows maps on shader model 2.0, I’d got a usual error message saying that “Arithmetic instruction limit of 64 exceeded“, so once again I have to find an instruction slot.

I had a code that tries to find the best shadow map for current pixel, something like:

//float2 map[] is a u/v pair; if it is "inside" the texture, I can use it
if (map[0].x < 0 || map[0].x > 1 || 
    map[0].y < 0 || map[0].y > 1)
{
  //...
}

This code was converted to:

//float2 map[] is a u/v pair; if it is "inside" the texture, I can use it
if( any (map[0]-saturate(map[0] ) ) )
{
  //...
}

This takes much less instructions, so now I have some free slots!

-1.#IND000000000000

komap — Wed, 11 May 2011 09:35:18 +0000

Q: In Visual Studio, how to set conditional breakpoint on -1.#IND000000000000 ?

 vairable == -1.#IND000000000000//this cannot work, of course

vairable != vairable

More productive programming

komap — Wed, 20 Apr 2011 09:00:17 +0000

(inspired by 10 best tricks of fooling myself to work and Create more productive environment at your desk)

Drink a good tea constantly.
it helps to concentrate. I recommend Pu-erh or Oolong)
Drink a your tea with no sugar.
not only it tastes much better (this is the only reasonable way to drink a tea), but also when it is accidentally spilled on a keyboard, the keyboard is recoverable, and the keys do not stick. Thus you will be significantly more productive than somebody who drinks tea/coffee with sugar (or Pepsi or whatever)
Keep your browser closed; get updates using RSS readers.
I personally had been spending a lot of time checking news sites/ /. / HN /Merriam-Webster’s Word of the Day/German word of the day/ Wik ipe dia watch list etc. each time “the code is compiling”, and then continue to surf. Now RSS saves me a lot of time.
Ask a co-worker for help, if you are stuck on a problem more than 30 minutes.
usually, you will find the solution even before you finish explaining him the issue. If not, you give him a chance to solve your problem and fill genius.
Use Ginkgo biloba, if you still feel dumb.
I don’t know whether it’ effect is fully Psychosomatic or not, but it helps.

HLSL trick #2

komap — Thu, 14 Apr 2011 14:55:39 +0000

Saving some expensive instruction in shader model 2…
(Trick #1 is described here)

Instead of, e. g.,

float getTotalDiffuse()
{
 float l1 = getDiffuse(g_light1);
 float l2 = getDiffuse(g_light2);
 float l3 = getDiffuse(g_light3);
 float l4 = getDiffuse(g_light4);
 return l1+l2+l3+l4;
}

try

float getTotalDiffuse()
{
 float4 l = {getDiffuse(g_light1),
              getDiffuse(g_light2),
              getDiffuse(g_light3),
              getDiffuse(g_light4)};
 return dot (l, float4(1,1,1,1));
}

The trick is that sometimes if you want to sum some floats (or vectors), it may be cheaper to use dot product with vector (1, … , 1)

HLSL trick

komap — Wed, 02 Mar 2011 16:44:54 +0000

If you write a HLSL Shader Model 2 you know you are limited to 32 const registers. Here is a trick that helped me to save one.

Suppose you want to write in pixel shader:

 float4x4 l_Color=
   {
      tex2D(samTex0, In.Tex0),
      tex2D(samTex1, In.Tex1),
      tex2D(samTex2, In.Tex2),
      tex2D(samTex3, In.Tex3)
   };
 ...
   l_Color[g_BlendLayer] = foo(l_Color[g_BlendLayer]); 
   //OOPS! illegal syntax
   out.Color = combine (Color);

But you cannot write in ShaderModel 2 “array[index] = blah“.

Second try:

   ...
  float4 blended = foo(l_Color[g_BlendLayer]);
   switch (BlendLayer)
   {
      case 0: l_Color[0] = blended; break;
      case 1: l_Color[1] = blended; break;
      case 2: l_Color[2] = blended; break;
      case 3: l_Color[3] = blended; break;
   }
   //OOPS! illegal syntax
   ...

Of course, there is no switch/case in ShaderModel 2…

   ...
  float4 blended = foo(l_Color[g_BlendLayer]);
   switch (BlendLayer)
   {
      case 0: l_Color[0] = blended; break;
      case 1: l_Color[1] = blended; break;
      case 2: l_Color[2] = blended; break;
      case 3: l_Color[3] = blended; break;
   }
   //OOPS! illegal syntax
   ...

Same problem: “array[index] = blah“.

   ...
  float4 blended = foo(l_Color[g_BlendLayer]);
  if (0 == BlendLayer) l_Color[0] = blended; else
  if (1 == BlendLayer) l_Color[1] = blended; else
  if (2 == BlendLayer) l_Color[2] = blended; else
  if (3 == BlendLayer) l_Color[3] = blended; 
   //OOPS! Too bad
   ...

Although this code is syntactically correct, it is wrong: condition are bad, and nested ifs are even worse (just look on disassembly). Too much instructions.

   ...
  float4 blended = foo(l_Color[g_BlendLayer]);
  if (0 == BlendLayer) l_Color[0] = blended; 
  if (1 == BlendLayer) l_Color[1] = blended; 
  if (2 == BlendLayer) l_Color[2] = blended; 
  if (3 == BlendLayer) l_Color[3] = blended; 
   //Much better!
   ...

This code (same as previous, but without “else”s, is much better. But still, I get “error X5589: Invalid const register num: 32. Max allowed is 31.”

   ...
  float4 blended = foo(l_Color[g_BlendLayer]);
  if (0 == BlendLayer--) l_Color[0] = blended; 
  if (0 == BlendLayer--) l_Color[1] = blended; 
  if (0 == BlendLayer--) l_Color[2] = blended; 
  if (0 == BlendLayer--) l_Color[3] = blended; 
   //It works!
   ...

Learning the assembly code really helps.
Here is how you get .asm files from your HLSL shaders,
using Microsoft’s fxc tool:

fxc /Gfp /Zi /T ps_2_0 /Fc out.asm l:\efx\mini.fx /E PS_Test

or, to get nice HTML:

fxc /Gfp /Zi /T ps_2_0 /Cc /Fc out.asm.html l:\efx\mini.fx /E PS_Test

words….

komap — Mon, 21 Feb 2011 13:06:20 +0000

unordered facts.

Etymology of etymology: Greek ἐτυμολογία (etumologíā); from ἔτυμον (étumon), meaning “true sense”, and -λογία (-logía), meaning “study”; from λόγος (lógos), meaning “speech, account, reason.” (wikipedia)

Pronunciation of pronunciation is IPA: /pɹəˌnʌnsiˈeɪʃən/, SAMPA: /pr@%nVnsi”eIS@n/ (wiktionary)

Doublet for doublet is twin.

The term antonym is synonymous with opposite.

Antonym to antonym is synonym.

There is no synonym to synonym, AFAIK.

TLA is TLA. (Three-letter acronym)

FLAB is FLAB (Four-letter abbreviation)

Onomatopoeic is not onomatopeic.

Awkward is an awkward word.

RAS syndrome is an example of RAS syndrome.

Portmanteau is Portmanteau.

hm.

heterological is not heterological nor autological.

Puzzle

komap — Tue, 24 Aug 2010 18:47:46 +0000

playing with JavaScript:
10-matchsticks puzzle

999…

komap — Mon, 08 Feb 2010 20:43:07 +0000

Question

Let N = any number not divisible by 2 and 5.
Does there exist a k (for each such N), such that 10^k – 1 is divisible by N?
Or: Is there 99..9 for any N, such as 99..9 is divisible by N, if N is coprime with 10?

Answer

Yes. It is multiplicative order of 10 modulo N. The sequence is can be found at The On-Line Encyclopedia of Integer Sequences.

Proof

Trivial.

Code


-- all numbers than cannot be devided by 2 or 5

seq1 :: [Integer]

seq1 = filter (\a->(a `mod` 10) `elem` [1,3,7,9]) [1..]
-- find 99..9 that can be devided by n

findNum::Integer->Integer

findNum n = head $ [x | x<-[1..], (10^x-1) `mod` n == 0]
 --prints the sequene

take 100 $ map findNum3 seq2