[babl] Make HCY conversions symmetric.

[Øyvind Kolås <ok src gnome org>]

commit 8a9231391cfdc564ceb3b792f9d4670b485a70b4
Author: SBP <vorstar mac com>
Date:   Thu May 4 15:10:04 2017 +0200

    Make HCY conversions symmetric.

 extensions/HCY.c       |    2 +-
 extensions/Makefile.am |    2 ++
 2 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/extensions/HCY.c b/extensions/HCY.c
index 51382ef..0993842 100644
--- a/extensions/HCY.c
+++ b/extensions/HCY.c
@@ -197,7 +197,7 @@ rgba_to_hcy_step (char *src,
     X = (rgb[ix[1]] - rgb[ix[0]]) / chroma;
 
     Y_peak = weights[ix[2]] + X * weights[ix[1]];
-    if (luma > 0. && luma < 1.)
+    if (luma != 0. && luma != 1.)
       chroma /= luma < Y_peak ? luma/Y_peak : (1. - luma)/(1. - Y_peak);
 
     hue = (H_sec + t * X) / 6.;
diff --git a/extensions/Makefile.am b/extensions/Makefile.am
index 923ddad..f09ec87 100644
--- a/extensions/Makefile.am
+++ b/extensions/Makefile.am
@@ -29,6 +29,7 @@ ext_LTLIBRARIES = \
        float.la        \
        fast-float.la   \
        naive-CMYK.la   \
+       HCY.la          \
        HSL.la          \
        HSV.la          \
        simple.la       \
@@ -52,6 +53,7 @@ gggl_la_SOURCES = gggl.c
 gimp_8bit_la_SOURCES = gimp-8bit.c
 grey_la_SOURCES = grey.c
 naive_CMYK_la_SOURCES = naive-CMYK.c
+HCY_la_SOURCES = HCY.c
 HSL_la_SOURCES = HSL.c
 HSV_la_SOURCES = HSV.c
 sse2_float_la_SOURCES = sse2-float.c