[babl] babl: use hashtable approach in double reference

[Øyvind Kolås <ok src gnome org>]

commit e3dda81e47376665c0034fe0bcd45e35601470df
Author: Øyvind Kolås <pippin gimp org>
Date:   Fri May 18 11:02:04 2018 +0200

    babl: use hashtable approach in double reference
    
    Strictly speaking we should be doing the reference using
    conversions to R'G'B'A double and using the distance metric
    there; possibly getting a slight difference in result at
    comparison ties.
    
    In use GEGL ends up using both the really fast 8bit code paths
    and the quite fast floating point code paths that use 8bit
    hashtables for the lookup of conversion.
    
    Progress on bug #787237 missing fast-paths.

 babl/babl-palette.c |  154 ++++++++++++++++++++------------------------------
 1 files changed, 62 insertions(+), 92 deletions(-)
---
diff --git a/babl/babl-palette.c b/babl/babl-palette.c
index a22ea58..ca375c9 100644
--- a/babl/babl-palette.c
+++ b/babl/babl-palette.c
@@ -28,13 +28,11 @@
 
 #define HASH_TABLE_SIZE 1111
 
-//#define SHOW_PATH
-
 /* A default palette, containing standard ANSI / EGA colors
  *
  */
-static unsigned char defpal_data[4*16] = 
-{  
+static unsigned char defpal_data[4*16] =
+{
 0  ,0  ,0  ,255,
 127,0  ,0  ,255,
 0  ,127,0  ,255,
@@ -77,6 +75,8 @@ babl_palette_reset_hash (BablPalette *pal)
     }
 }
 
+#define BABL_IDX_FACTOR 255.5
+
 static int
 babl_palette_lookup (BablPalette *pal, int r, int g, int b, int a)
 {
@@ -180,108 +180,92 @@ static BablPalette *default_palette (void)
 
 static void
 rgba_to_pal (Babl *conversion,
-             char *src,
+             char *src_b,
              char *dst,
              long  n,
              void *dst_model_data)
 {
+  const Babl *space = babl_conversion_get_source_space (conversion);
   BablPalette **palptr = dst_model_data;
-  BablPalette *pal = *palptr;
-#ifdef SHOW_PATH
-  fprintf (stderr, "d");
-#endif
+  BablPalette *pal;
+  assert (palptr);
+  pal = *palptr;
+  assert(pal);
+
   while (n--)
     {
-      int idx;
-
-      int best_idx = 0;
-      double best_diff = 100000;
-      double srcf[4];
+      double *src_d = (void*) src_b;
+      unsigned char src[4];
       int c;
-      for (c = 0; c < 4; c++)
+      for (c = 0; c < 3; c++)
       {
-        srcf[c] = ((double *) src)[c];
-        if (srcf[c] < 0.0)
-         srcf[c] = 0.0;
-        if (srcf[c] > 1.0)
-         srcf[c] = 1.0;
+        if (src_d[c] >= 1.0f)
+          src[c] = 255;
+        else if (src_d[c] <= 0.0f)
+          src[c] = 0;
+        else
+          src[c] = babl_trc_from_linear (space->space.trc[0],
+                                         src_d[c]) * 255 + 0.5f;
       }
+      if (src_d[3] >= 1.0f)
+        src[3] = 255;
+      else if (src_d[3] <= 0.0f)
+        src[3] = 0;
+      else
+        src[3] = src_d[3] * 255 + 0.5f;
 
-      for (idx = 0; idx<pal->count; idx++)
-        {
-          double diff;
-          double *palpx = ((double *)pal->data_double) + idx * 4;
-
-          diff = (palpx[0] - srcf[0]) * (palpx[0] - srcf[0]) +
-                 (palpx[1] - srcf[1]) * (palpx[1] - srcf[1]) +
-                 (palpx[2] - srcf[2]) * (palpx[2] - srcf[2]);
-          if (diff <= best_diff)
-            {
-              best_diff = diff;
-              best_idx = idx;
-            }
-        }
-
-      ((double *) dst)[0] = best_idx / 255.5;
+      ((double *) dst)[0] =
+        babl_palette_lookup (pal, src[0], src[1], src[2], src[3]) /
+           BABL_IDX_FACTOR;
 
-      src += sizeof (double) * 4;
+      src_b += sizeof (double) * 4;
       dst += sizeof (double) * 1;
     }
+
 }
 
 static void
 rgba_to_pala (Babl *conversion,
-              char *src,
+              char *src_i,
               char *dst,
               long  n,
               void *dst_model_data)
 {
+  const Babl *space = babl_conversion_get_destination_space (conversion);
   BablPalette **palptr = dst_model_data;
-  BablPalette *pal = *palptr;
-
-#ifdef SHOW_PATH
-  fprintf (stderr, "D");
-#endif
+  BablPalette *pal;
+  assert (palptr);
+  pal = *palptr;
   assert(pal);
+
   while (n--)
     {
-      int idx;
-
-      int best_idx = 0;
-      double best_diff = 100000;
-      double srcf[4];
-      double alpha;
+      double *src_d = (void*) src_i;
+      unsigned char src[4];
       int c;
-      for (c = 0; c < 4; c++)
+      for (c = 0; c < 3; c++)
       {
-        srcf[c] = ((double *) src)[c];
-        if (srcf[c] < 0.0)
-         srcf[c] = 0.0;
-        if (srcf[c] > 1.0)
-         srcf[c] = 1.0;
+        if (src_d[c] >= 1.0f)
+          src[c] = 255;
+        else if (src_d[c] <= 0.0f)
+          src[c] = 0;
+        else
+          src[c] = babl_trc_from_linear (space->space.trc[0],
+                                         src_d[c]) * 255 + 0.5f;
       }
+      if (src_d[3] >= 1.0f)
+        src[3] = 255;
+      else if (src_d[3] <= 0.0f)
+        src[3] = 0;
+      else
+        src[3] = src_d[3] * 255 + 0.5f;
 
-      alpha = srcf[3];
-
-      for (idx = 0; idx<pal->count; idx++)
-        {
-          double diff;
-          double *palpx = ((double *)pal->data_double) + idx * 4;
-
-          diff = (palpx[0] - srcf[0]) * (palpx[0] - srcf[0]) +
-                 (palpx[1] - srcf[1]) * (palpx[1] - srcf[1]) +
-                 (palpx[2] - srcf[2]) * (palpx[2] - srcf[2]);
-          if (diff <= best_diff)
-            {
-              best_diff = diff;
-              best_idx = idx;
-            }
-        }
 
-      ((double *) dst)[0] = best_idx / 255.5;
-      ((double *) dst)[1] = alpha;
+      ((double *) dst)[0] = babl_palette_lookup (pal, src[0], src[1], src[2],
+                                                 src[3]) / BABL_IDX_FACTOR;
+      ((double *) dst)[1] = src_d[3];
 
-      src += sizeof (double) * 4;
+      src_i += sizeof (double) * 4;
       dst += sizeof (double) * 2;
     }
 }
@@ -298,7 +282,7 @@ pal_to_rgba (Babl *conversion,
   assert(pal);
   while (n--)
     {
-      int idx = (((double *) src)[0]) * 255.5;
+      int idx = (((double *) src)[0]) * BABL_IDX_FACTOR;
       double *palpx;
 
       if (idx < 0) idx = 0;
@@ -325,7 +309,7 @@ pala_to_rgba (Babl *conversion,
   assert(pal);
   while (n--)
     {
-      int idx      = (((double *) src)[0]) * 255.5;
+      int idx      = (((double *) src)[0]) * BABL_IDX_FACTOR;
       double alpha = (((double *) src)[1]);
       double *palpx;
 
@@ -354,9 +338,7 @@ rgba_u8_to_pal (Babl          *conversion,
   assert (palptr);
   pal = *palptr;
   assert(pal);
-#ifdef SHOW_PATH
-  fprintf (stderr, "8");
-#endif
+
   while (n--)
     {
       dst[0] = babl_palette_lookup (pal, src[0], src[1], src[2], src[3]);
@@ -380,9 +362,6 @@ rgba_float_to_pal_a (Babl          *conversion,
   pal = *palptr;
   assert(pal);
 
-#ifdef SHOW_PATH
-  fprintf (stderr, "f");
-#endif
   while (n--)
     {
       float *src_f = (void*) src_b;
@@ -428,9 +407,7 @@ rgba_float_to_pal (Babl          *conversion,
   assert (palptr);
   pal = *palptr;
   assert(pal);
-#ifdef SHOW_PATH
-  fprintf (stderr, "F");
-#endif
+
   while (n--)
     {
       float *src_f = (void*) src_b;
@@ -630,7 +607,6 @@ const Babl *babl_new_palette (const char  *name,
     "chroma",
     NULL);
   alpha = babl_component ("A");
-  
   model = babl_model_new ("name", name, component, alpha, NULL);
   palptr = malloc (sizeof (void*));
   *palptr = default_palette ();;
@@ -678,30 +654,24 @@ const Babl *babl_new_palette (const char  *name,
      "data", palptr,
      NULL
   );
-
   babl_conversion_new (
      f_pal_u8,
      f_pal_a_u8,
      "linear", conv_pal8_pala8,
      NULL
   );
-
   babl_conversion_new (
      f_pal_a_u8,
      f_pal_u8,
      "linear", conv_pala8_pal8,
      NULL
   );
-
-
   babl_conversion_new (
      f_pal_u8,
      babl_format ("R'G'B'A u8"),
      "linear", pal_u8_to_rgba_u8,
      "data", palptr,
      NULL);
-
-
   babl_conversion_new (
      f_pal_a_u8,
      babl_format ("R'G'B'A u8"),