text: //========= Copyright Valve Corporation, All rights reserved. ============//
  //
  // Purpose: Color conversion routines.
  //
  //=====================================================================================//
  
  #include <math.h>
  #include <float.h>  // Needed for FLT_EPSILON
  #include "basetypes.h"
  #include <memory.h>
  #include "tier0/dbg.h"
  #include "mathlib/mathlib.h"
  #include "mathlib/vector.h"
  
  // memdbgon must be the last include file in a .cpp file!!!
  #include "tier0/memdbgon.h"
  
  //-----------------------------------------------------------------------------
  // Gamma conversion support
  //-----------------------------------------------------------------------------
  static byte     texgammatable[256]; // palette is sent through this to convert to screen gamma
  
  static float    texturetolinear[256];   // texture (0..255) to linear (0..1)
  static int      lineartotexture[1024];  // linear (0..1) to texture (0..255)
  static int      lineartoscreen[1024];   // linear (0..1) to gamma corrected vertex light (0..255)
  
  // build a lightmap texture to combine with surface texture, adjust for src*dst+dst*src, ramp reprogramming, etc
  float           lineartovertex[4096];   // linear (0..4) to screen corrected vertex space (0..1?)
  unsigned char   lineartolightmap[4096]; // linear (0..4) to screen corrected texture value (0..255)
  
  static float    g_Mathlib_GammaToLinear[256];   // gamma (0..1) to linear (0..1)
  static float    g_Mathlib_LinearToGamma[256];   // linear (0..1) to gamma (0..1)
  
  // This is aligned to 16-byte boundaries so that we can load it
  // onto SIMD registers easily if needed (used by SSE version of lightmaps)
  // TODO: move this into the one DLL that actually uses it, instead of statically
  // linking it everywhere via mathlib.
  ALIGN128 float  power2_n[256] =             // 2**(index - 128) / 255
  {
      1.152445441982634800E-041, 2.304890883965269600E-041, 4.609781767930539200E-041, 9.219563535861078400E-041,
      1.843912707172215700E-040, 3.687825414344431300E-040, 7.375650828688862700E-040, 1.475130165737772500E-039,
      2.950260331475545100E-039, 5.900520662951090200E-039, 1.180104132590218000E-038, 2.360208265180436100E-038,
      4.720416530360872100E-038, 9.440833060721744200E-038, 1.888166612144348800E-037, 3.776333224288697700E-037,
      7.552666448577395400E-037, 1.510533289715479100E-036, 3.021066579430958200E-036, 6.042133158861916300E-036,
      1.208426631772383300E-035, 2.416853263544766500E-035, 4.833706527089533100E-035, 9.667413054179066100E-035,
      1.933482610835813200E-034, 3.866965221671626400E-034, 7.733930443343252900E-034, 1.546786088668650600E-033,
      3.093572177337301200E-033, 6.187144354674602300E-033, 1.237428870934920500E-032, 2.474857741869840900E-032,
      4.949715483739681800E-032, 9.899430967479363700E-032, 1.979886193495872700E-031, 3.959772386991745500E-031,
      7.919544773983491000E-031, 1.583908954796698200E-030, 3.167817909593396400E-030, 6.335635819186792800E-030,
      1.267127163837358600E-029, 2.534254327674717100E-029, 5.068508655349434200E-029, 1.013701731069886800E-028,
      2.027403462139773700E-028, 4.054806924279547400E-028, 8.109613848559094700E-028, 1.621922769711818900E-027,
      3.243845539423637900E-027, 6.487691078847275800E-027, 1.297538215769455200E-026, 2.595076431538910300E-026,
      5.190152863077820600E-026, 1.038030572615564100E-025, 2.076061145231128300E-025, 4.152122290462256500E-025,
      8.304244580924513000E-025, 1.660848916184902600E-024, 3.321697832369805200E-024, 6.643395664739610400E-024,
      1.328679132947922100E-023, 2.657358265895844200E-023, 5.314716531791688300E-023, 1.062943306358337700E-022,
      2.125886612716675300E-022, 4.251773225433350700E-022, 8.503546450866701300E-022, 1.700709290173340300E-021,
      3.401418580346680500E-021, 6.802837160693361100E-021, 1.360567432138672200E-020, 2.721134864277344400E-020,
      5.442269728554688800E-020, 1.088453945710937800E-019, 2.176907891421875500E-019, 4.353815782843751100E-019,
      8.707631565687502200E-019, 1.741526313137500400E-018, 3.483052626275000900E-018, 6.966105252550001700E-018,
      1.393221050510000300E-017, 2.786442101020000700E-017, 5.572884202040001400E-017, 1.114576840408000300E-016,
      2.229153680816000600E-016, 4.458307361632001100E-016, 8.916614723264002200E-016, 1.783322944652800400E-015,
      3.566645889305600900E-015, 7.133291778611201800E-015, 1.426658355722240400E-014, 2.853316711444480700E-014,
      5.706633422888961400E-014, 1.141326684577792300E-013, 2.282653369155584600E-013, 4.565306738311169100E-013,
      9.130613476622338300E-013, 1.826122695324467700E-012, 3.652245390648935300E-012, 7.304490781297870600E-012,
      1.460898156259574100E-011, 2.921796312519148200E-011, 5.843592625038296500E-011, 1.168718525007659300E-010,
      2.337437050015318600E-010, 4.674874100030637200E-010, 9.349748200061274400E-010, 1.869949640012254900E-009,
      3.739899280024509800E-009, 7.479798560049019500E-009, 1.495959712009803900E-008, 2.991919424019607800E-008,
      5.983838848039215600E-008, 1.196767769607843100E-007, 2.393535539215686200E-007, 4.787071078431372500E-007,
      9.574142156862745000E-007, 1.914828431372549000E-006, 3.829656862745098000E-006, 7.659313725490196000E-006,
      1.531862745098039200E-005, 3.063725490196078400E-005, 6.127450980392156800E-005, 1.225490196078431400E-004,
      2.450980392156862700E-004, 4.901960784313725400E-004, 9.803921568627450800E-004, 1.960784313725490200E-003,
      3.921568627450980300E-003, 7.843137254901960700E-003, 1.568627450980392100E-002, 3.137254901960784300E-002,
      6.274509803921568500E-002, 1.254901960784313700E-001, 2.509803921568627400E-001, 5.019607843137254800E-001,
      1.003921568627451000E+000, 2.007843137254901900E+000, 4.015686274509803900E+000, 8.031372549019607700E+000,
      1.606274509803921500E+001, 3.212549019607843100E+001, 6.425098039215686200E+001, 1.285019607843137200E+002,
      2.570039215686274500E+002, 5.140078431372548900E+002, 1.028015686274509800E+003, 2.056031372549019600E+003,
      4.112062745098039200E+003, 8.224125490196078300E+003, 1.644825098039215700E+004, 3.289650196078431300E+004,
      6.579300392156862700E+004, 1.315860078431372500E+005, 2.631720156862745100E+005, 5.263440313725490100E+005,
      1.052688062745098000E+006, 2.105376125490196000E+006, 4.210752250980392100E+006, 8.421504501960784200E+006,
      1.684300900392156800E+007, 3.368601800784313700E+007, 6.737203601568627400E+007, 1.347440720313725500E+008,
      2.694881440627450900E+008, 5.389762881254901900E+008, 1.077952576250980400E+009, 2.155905152501960800E+009,
      4.311810305003921500E+009, 8.623620610007843000E+009, 1.724724122001568600E+010, 3.449448244003137200E+010,
      6.898896488006274400E+010, 1.379779297601254900E+011, 2.759558595202509800E+011, 5.519117190405019500E+011,
      1.103823438081003900E+012, 2.207646876162007800E+012, 4.415293752324015600E+012, 8.830587504648031200E+012,
      1.766117500929606200E+013, 3.532235001859212500E+013, 7.064470003718425000E+013, 1.412894000743685000E+014,
      2.825788001487370000E+014, 5.651576002974740000E+014, 1.130315200594948000E+015, 2.260630401189896000E+015,
      4.521260802379792000E+015, 9.042521604759584000E+015, 1.808504320951916800E+016, 3.617008641903833600E+016,
      7.234017283807667200E+016, 1.446803456761533400E+017, 2.893606913523066900E+017, 5.787213827046133800E+017,
      1.157442765409226800E+018, 2.314885530818453500E+018, 4.629771061636907000E+018, 9.259542123273814000E+018,
      1.851908424654762800E+019, 3.703816849309525600E+019, 7.407633698619051200E+019, 1.481526739723810200E+020,
      2.963053479447620500E+020, 5.926106958895241000E+020, 1.185221391779048200E+021, 2.370442783558096400E+021,
      4.740885567116192800E+021, 9.481771134232385600E+021, 1.896354226846477100E+022, 3.792708453692954200E+022,
      7.585416907385908400E+022, 1.517083381477181700E+023, 3.034166762954363400E+023, 6.068333525908726800E+023,
      1.213666705181745400E+024, 2.427333410363490700E+024, 4.854666820726981400E+024, 9.709333641453962800E+024,
      1.941866728290792600E+025, 3.883733456581585100E+025, 7.767466913163170200E+025, 1.553493382632634000E+026,
      3.106986765265268100E+026, 6.213973530530536200E+026, 1.242794706106107200E+027, 2.485589412212214500E+027,
      4.971178824424429000E+027, 9.942357648848857900E+027, 1.988471529769771600E+028, 3.976943059539543200E+028,
      7.953886119079086300E+028, 1.590777223815817300E+029, 3.181554447631634500E+029, 6.363108895263269100E+029,
      1.272621779052653800E+030, 2.545243558105307600E+030, 5.090487116210615300E+030, 1.018097423242123100E+031,
      2.036194846484246100E+031, 4.072389692968492200E+031, 8.144779385936984400E+031, 1.628955877187396900E+032,
      3.257911754374793800E+032, 6.515823508749587500E+032, 1.303164701749917500E+033, 2.606329403499835000E+033,
      5.212658806999670000E+033, 1.042531761399934000E+034, 2.085063522799868000E+034, 4.170127045599736000E+034,
      8.340254091199472000E+034, 1.668050818239894400E+035, 3.336101636479788800E+035, 6.672203272959577600E+035
  };
  
  // You can use this to double check the exponent table and assert that
  // the precomputation is correct.
  #ifdef DBGFLAG_ASSERT
  #pragma warning(push)
  #pragma warning( disable : 4189 ) // disable unused local variable warning
  static void CheckExponentTable()
  {
      for( int i = 0; i < 256; i++ )
      {
          float testAgainst = pow( 2.0f, i - 128 ) / 255.0f;
          float diff = testAgainst - power2_n[i] ;
          float relativeDiff = diff / testAgainst;
          Assert( testAgainst == 0 ?
                  power2_n[i] < 1.16E-041 :
                  power2_n[i] == testAgainst );
      }
  }
  #pragma warning(pop)
  #endif
  
  void BuildGammaTable( float gamma, float texGamma, float brightness, int overbright )
  {
      int     i, inf;
      float   g1, g3;
  
      // Con_Printf("BuildGammaTable %.1f %.1f %.1f\n", g, v_lightgamma.GetFloat(), v_texgamma.GetFloat() );
  
      float g = gamma;
      if (g > 3.0)
      {
          g = 3.0;
      }
  
      g = 1.0 / g;
      g1 = texGamma * g;
  
      if (brightness <= 0.0)
      {
          g3 = 0.125;
      }
      else if (brightness > 1.0)
      {
          g3 = 0.05;
      }
      else
      {
          g3 = 0.125 - (brightness * brightness) * 0.075;
      }
  
      for (i=0 ; i<256 ; i++)
      {
          inf = 255 * pow ( i/255.f, g1 );
          if (inf < 0)
              inf = 0;
          if (inf > 255)
              inf = 255;
          texgammatable[i] = inf;
      }
  
      for (i=0 ; i<1024 ; i++)
      {
          float f;
  
          f = i / 1023.0;
  
          // scale up
          if (brightness > 1.0)
              f = f * brightness;
  
          // shift up
          if (f <= g3)
              f = (f / g3) * 0.125;
          else
              f = 0.125 + ((f - g3) / (1.0 - g3)) * 0.875;
  
          // convert linear space to desired gamma space
          inf = 255 * pow ( f, g );
  
          if (inf < 0)
              inf = 0;
          if (inf > 255)
              inf = 255;
          lineartoscreen[i] = inf;
      }
  
      /*
      for (i=0 ; i<1024 ; i++)
      {
          // convert from screen gamma space to linear space
          lineargammatable[i] = 1023 * pow ( i/1023.0, v_gamma.GetFloat() );
          // convert from linear gamma space to screen space
          screengammatable[i] = 1023 * pow ( i/1023.0, 1.0 / v_gamma.GetFloat() );
      }
      */
  
      for (i=0 ; i<256 ; i++)
      {
          // convert from nonlinear texture space (0..255) to linear space (0..1)
          texturetolinear[i] =  pow( i / 255.f, texGamma );
  
          // convert from linear space (0..1) to nonlinear (sRGB) space (0..1)
          g_Mathlib_LinearToGamma[i] =  LinearToGammaFullRange( i / 255.f );
  
          // convert from sRGB gamma space (0..1) to linear space (0..1)
          g_Mathlib_GammaToLinear[i] =  GammaToLinearFullRange( i / 255.f );
      }
  
      for (i=0 ; i<1024 ; i++)
      {
          // convert from linear space (0..1) to nonlinear texture space (0..255)
          lineartotexture[i] =  pow( i / 1023.0, 1.0 / texGamma ) * 255;
      }
  
  #if 0
      for (i=0 ; i<256 ; i++)
      {
          float f;
  
          // convert from nonlinear lightmap space (0..255) to linear space (0..4)
          // f =  (i / 255.0) * sqrt( 4 );
          f =  i * (2.0 / 255.0);
          f = f * f;
  
          texlighttolinear[i] = f;
      }
  #endif
  
      {
          float f;
          float overbrightFactor = 1.0f;
  
          // Can't do overbright without texcombine
          // UNDONE: Add GAMMA ramp to rectify this
          if ( overbright == 2 )
          {
              overbrightFactor = 0.5;
          }
          else if ( overbright == 4 )
          {
              overbrightFactor = 0.25;
          }
  
          for (i=0 ; i<4096 ; i++)
          {
              // convert from linear 0..4 (x1024) to screen corrected vertex space (0..1?)
              f = pow ( i/1024.0, 1.0 / gamma );
  
              lineartovertex[i] = f * overbrightFactor;
              if (lineartovertex[i] > 1)
                  lineartovertex[i] = 1;
  
              int nLightmap = RoundFloatToInt( f * 255 * overbrightFactor );
              nLightmap = clamp( nLightmap, 0, 255 );
              lineartolightmap[i] = (unsigned char)nLightmap;
          }
      }
  }
  
  float GammaToLinearFullRange( float gamma )
  {
      return pow( gamma, 2.2f );
  }
  
  float LinearToGammaFullRange( float linear )
  {
      return pow( linear, 1.0f / 2.2f );
  }
  
  float GammaToLinear( float gamma )
  {
      Assert( s_bMathlibInitialized );
      if ( gamma < 0.0f )
      {
          return 0.0f;
      }
  
      if ( gamma >= 0.95f )
      {
          // Use GammaToLinearFullRange maybe if you trip this.
  // X360TEMP
  //      Assert( gamma <= 1.0f );
          return 1.0f;
      }
  
      int index = RoundFloatToInt( gamma * 255.0f );
      Assert( index >= 0 && index < 256 );
      return g_Mathlib_GammaToLinear[index];
  }
  
  float LinearToGamma( float linear )
  {
      Assert( s_bMathlibInitialized );
      if ( linear < 0.0f )
      {
          return 0.0f;
      }
      if ( linear > 1.0f )
      {
          // Use LinearToGammaFullRange maybe if you trip this.
          Assert( 0 );
          return 1.0f;
      }
  
      int index = RoundFloatToInt( linear * 255.0f );
      Assert( index >= 0 && index < 256 );
      return g_Mathlib_LinearToGamma[index];
  }
  
  //-----------------------------------------------------------------------------
  // Helper functions to convert between sRGB and 360 gamma space
  //-----------------------------------------------------------------------------
  float SrgbGammaToLinear( float flSrgbGammaValue )
  {
      float x = clamp( flSrgbGammaValue, 0.0f, 1.0f );
      return ( x <= 0.04045f ) ? ( x / 12.92f ) : ( pow( ( x + 0.055f ) / 1.055f, 2.4f ) );
  }
  
  float SrgbLinearToGamma( float flLinearValue )
  {
      float x = clamp( flLinearValue, 0.0f, 1.0f );
      return ( x <= 0.0031308f ) ? ( x * 12.92f ) : ( 1.055f * pow( x, ( 1.0f / 2.4f ) ) ) - 0.055f;
  }
  
  float X360GammaToLinear( float fl360GammaValue )
  {
      float flLinearValue;
  
      fl360GammaValue = clamp( fl360GammaValue, 0.0f, 1.0f );
      if ( fl360GammaValue < ( 96.0f / 255.0f ) )
      {
          if ( fl360GammaValue < ( 64.0f / 255.0f ) )
          {
              flLinearValue = fl360GammaValue * 255.0f;
          }
          else
          {
              flLinearValue = fl360GammaValue * ( 255.0f * 2.0f ) - 64.0f;
              flLinearValue += floor( flLinearValue * ( 1.0f / 512.0f ) );
          }
      }
      else
      {
          if( fl360GammaValue < ( 192.0f / 255.0f ) )
          {
              flLinearValue = fl360GammaValue * ( 255.0f * 4.0f ) - 256.0f;
              flLinearValue += floor( flLinearValue * ( 1.0f / 256.0f ) );
          }
          else
          {
              flLinearValue = fl360GammaValue * ( 255.0f * 8.0f ) - 1024.0f;
              flLinearValue += floor( flLinearValue * ( 1.0f / 128.0f ) );
          }
      }
  
      flLinearValue *= 1.0f / 1023.0f;
  
      flLinearValue = clamp( flLinearValue, 0.0f, 1.0f );
      return flLinearValue;
  }
  
  float X360LinearToGamma( float flLinearValue )
  {
      float fl360GammaValue;
  
      flLinearValue = clamp( flLinearValue, 0.0f, 1.0f );
      if ( flLinearValue < ( 128.0f / 1023.0f ) )
      {
          if ( flLinearValue < ( 64.0f / 1023.0f ) )
          {
              fl360GammaValue = flLinearValue * ( 1023.0f * ( 1.0f / 255.0f ) );
          }
          else
          {
              fl360GammaValue = flLinearValue * ( ( 1023.0f / 2.0f ) * ( 1.0f / 255.0f ) ) + ( 32.0f / 255.0f );
          }
      }
      else
      {
          if ( flLinearValue < ( 512.0f / 1023.0f ) )
          {
              fl360GammaValue = flLinearValue * ( ( 1023.0f / 4.0f ) * ( 1.0f / 255.0f ) ) + ( 64.0f / 255.0f );
          }
          else
          {
              fl360GammaValue = flLinearValue * ( ( 1023.0f /8.0f ) * ( 1.0f / 255.0f ) ) + ( 128.0f /255.0f ); // 1.0 -> 1.0034313725490196078431372549016
              if ( fl360GammaValue > 1.0f )
              {
                  fl360GammaValue = 1.0f;
              }
          }
      }
  
      fl360GammaValue = clamp( fl360GammaValue, 0.0f, 1.0f );
      return fl360GammaValue;
  }
  
  float SrgbGammaTo360Gamma( float flSrgbGammaValue )
  {
      float flLinearValue = SrgbGammaToLinear( flSrgbGammaValue );
      float fl360GammaValue = X360LinearToGamma( flLinearValue );
      return fl360GammaValue;
  }
  
  // convert texture to linear 0..1 value
  float TextureToLinear( int c )
  {
      Assert( s_bMathlibInitialized );
      if (c < 0)
          return 0;
      if (c > 255)
          return 1.0;
  
      return texturetolinear[c];
  }
  
  // convert texture to linear 0..1 value
  int LinearToTexture( float f )
  {
      Assert( s_bMathlibInitialized );
      int i;
      i = f * 1023;   // assume 0..1 range
      if (i < 0)
          i = 0;
      if (i > 1023)
          i = 1023;
  
      return lineartotexture[i];
  }
  
  
  // converts 0..1 linear value to screen gamma (0..255)
  int LinearToScreenGamma( float f )
  {
      Assert( s_bMathlibInitialized );
      int i;
      i = f * 1023;   // assume 0..1 range
      if (i < 0)
          i = 0;
      if (i > 1023)
          i = 1023;
  
      return lineartoscreen[i];
  }
  
  void ColorRGBExp32ToVector( const ColorRGBExp32& in, Vector& out )
  {
      Assert( s_bMathlibInitialized );
      // FIXME: Why is there a factor of 255 built into this?
      out.x = 255.0f * TexLightToLinear( in.r, in.exponent );
      out.y = 255.0f * TexLightToLinear( in.g, in.exponent );
      out.z = 255.0f * TexLightToLinear( in.b, in.exponent );
  }
  
  #if 0
  // assumes that the desired mantissa range is 128..255
  static int VectorToColorRGBExp32_CalcExponent( float in )
  {
      int power = 0;
  
      if( in != 0.0f )
      {
          while( in > 255.0f )
          {
              power += 1;
              in *= 0.5f;
          }
  
          while( in < 128.0f )
          {
              power -= 1;
              in *= 2.0f;
          }
      }
  
      return power;
  }
  
  void VectorToColorRGBExp32( const Vector& vin, ColorRGBExp32 &c )
  {
      Vector v = vin;
      Assert( s_bMathlibInitialized );
      Assert( v.x >= 0.0f && v.y >= 0.0f && v.z >= 0.0f );
      int i;
      float max = v[0];
      for( i = 1; i < 3; i++ )
      {
          // Get the maximum value.
          if( v[i] > max )
          {
              max = v[i];
          }
      }
  
      // figure out the exponent for this luxel.
      int exponent = VectorToColorRGBExp32_CalcExponent( max );
  
      // make the exponent fits into a signed byte.
      if( exponent < -128 )
      {
          exponent = -128;
      }
      else if( exponent > 127 )
      {
          exponent = 127;
      }
  
      // undone: optimize with a table
      float scalar = pow( 2.0f, -exponent );
      // convert to mantissa x 2^exponent format
      for( i = 0; i < 3; i++ )
      {
          v[i] *= scalar;
          // clamp
          if( v[i] > 255.0f )
          {
              v[i] = 255.0f;
          }
      }
      c.r = ( unsigned char )v[0];
      c.g = ( unsigned char )v[1];
      c.b = ( unsigned char )v[2];
      c.exponent = ( signed char )exponent;
  }
  
  #else
  
  // given a floating point number  f, return an exponent e such that
  // for f' = f * 2^e,  f is on [128..255].
  // Uses IEEE 754 representation to directly extract this information
  // from the float.
  inline static int VectorToColorRGBExp32_CalcExponent( const float *pin )
  {
      // The thing we will take advantage of here is that the exponent component
      // is stored in the float itself, and because we want to map to 128..255, we
      // want an "ideal" exponent of 2^7. So, we compute the difference between the
      // input exponent and 7 to work out the normalizing exponent. Thus if you pass in
      // 32 (represented in IEEE 754 as 2^5), this function will return 2
      // (because 32 * 2^2 = 128)
      if (*pin == 0.0f)
          return 0;
  
      unsigned int fbits = *reinterpret_cast<const unsigned int *>(pin);
  
      // the exponent component is bits 23..30, and biased by +127
      const unsigned int biasedSeven = 7 + 127;
  
      signed int expComponent = ( fbits & 0x7F800000 ) >> 23;
      expComponent -= biasedSeven; // now the difference from seven (positive if was less than, etc)
      return expComponent;
  }
  
  
  
  /// Slightly faster version of the function to turn a float-vector color into
  /// a compressed-exponent notation 32bit color. However, still not SIMD optimized.
  /// PS3 developer: note there is a movement of a float onto an int here, which is
  /// bad on the base registers -- consider doing this as Altivec code, or better yet
  /// moving it onto the cell.
  /// \warning: Assumes an IEEE 754 single-precision float representation! Those of you
  /// porting to an 8080 are out of luck.
  void VectorToColorRGBExp32( const Vector& vin, ColorRGBExp32 &c )
  {
      Assert( s_bMathlibInitialized );
      Assert( vin.x >= 0.0f && vin.y >= 0.0f && vin.z >= 0.0f );
  
      // work out which of the channels is the largest ( we will use that to map the exponent )
      // this is a sluggish branch-based decision tree -- most architectures will offer a [max]
      // assembly opcode to do this faster.
      const float *pMax;
      if (vin.x > vin.y)
      {
          if (vin.x > vin.z)
          {
              pMax = &vin.x;
          }
          else
          {
              pMax = &vin.z;
          }
      }
      else
      {
          if (vin.y > vin.z)
          {
              pMax = &vin.y;
          }
          else
          {
              pMax = &vin.z;
          }
      }
  
      // now work out the exponent for this luxel.
      signed int exponent = VectorToColorRGBExp32_CalcExponent( pMax );
  
      // make sure the exponent fits into a signed byte.
      // (in single precision format this is assured because it was a signed byte to begin with)
      Assert(exponent > -128 && exponent <= 127);
  
      // promote the exponent back onto a scalar that we'll use to normalize all the numbers
      float scalar;
      {
          unsigned int fbits = (127 - exponent) << 23;
          scalar = *reinterpret_cast<float *>(&fbits);
      }
  
      // we should never need to clamp:
      Assert(vin.x * scalar <= 255.0f &&
             vin.y * scalar <= 255.0f &&
             vin.z * scalar <= 255.0f);
  
      // This awful construction is necessary to prevent VC2005 from using the
      // fldcw/fnstcw control words around every float-to-unsigned-char operation.
      {
          int red = (vin.x * scalar);
          int green = (vin.y * scalar);
          int blue = (vin.z * scalar);
  
          c.r = red;
          c.g = green;
          c.b = blue;
      }
      /*
      c.r = ( unsigned char )(vin.x * scalar);
      c.g = ( unsigned char )(vin.y * scalar);
      c.b = ( unsigned char )(vin.z * scalar);
      */
  
      c.exponent = ( signed char )exponent;
  }
  
  #endif
  