[gthumb: 35/129] added CAIRO_SET_RGBA_FAST macro that uses shift and add to divide by 255

[Paolo Bacchilega <paobac src gnome org>]

commit b84eae853e5a71fed0bf6fbf20e550555daea6b2
Author: Paolo Bacchilega <paobac src gnome org>
Date:   Sun Apr 17 13:26:39 2011 +0200

    added CAIRO_SET_RGBA_FAST macro that uses shift and add to divide by 255

 gthumb/cairo-utils.c |    3 +-
 gthumb/cairo-utils.h |   66 ++++++++++++++++++++++++++++++++-----------------
 2 files changed, 45 insertions(+), 24 deletions(-)
---
diff --git a/gthumb/cairo-utils.c b/gthumb/cairo-utils.c
index 98c8e91..2947164 100644
--- a/gthumb/cairo-utils.c
+++ b/gthumb/cairo-utils.c
@@ -192,6 +192,7 @@ _cairo_image_surface_create_from_pixbuf (GdkPixbuf *pixbuf)
 	int                      s_stride;
 	unsigned char           *s_pixels;
 	int                      h, w;
+	unsigned int             t;
 
 	if (pixbuf == NULL)
 		return NULL;
@@ -220,7 +221,7 @@ _cairo_image_surface_create_from_pixbuf (GdkPixbuf *pixbuf)
 			p_iter = p_pixels;
 
 			for (w = 0; w < width; w++) {
-				CAIRO_SET_RGBA (s_iter, p_iter[0], p_iter[1], p_iter[2], p_iter[3]);
+				CAIRO_SET_RGBA_FAST (s_iter, p_iter[0], p_iter[1], p_iter[2], p_iter[3], t);
 
 				s_iter += 4;
 				p_iter += p_n_channels;
diff --git a/gthumb/cairo-utils.h b/gthumb/cairo-utils.h
index a1f3d5c..3408c09 100644
--- a/gthumb/cairo-utils.h
+++ b/gthumb/cairo-utils.h
@@ -53,39 +53,59 @@
 #endif
 
 #define CAIRO_SET_RGB(pixel, red, green, blue)					\
-	do {									\
-		pixel[CAIRO_RED]   = (red);					\
+	G_STMT_START {								\
+		pixel[CAIRO_RED] = (red);					\
 		pixel[CAIRO_GREEN] = (green);					\
-		pixel[CAIRO_BLUE]  = (blue);					\
+		pixel[CAIRO_BLUE] = (blue);					\
 		pixel[CAIRO_ALPHA] = 0xff;					\
-	} while (0)
+	} G_STMT_END
 
 #define CAIRO_SET_RGBA(pixel, red, green, blue, alpha)				\
-	do {									\
-		gdouble alpha_factor = (gdouble) alpha / 0xff;			\
-		pixel[CAIRO_RED]   = (guchar) (alpha_factor * (red) + .5);	\
-		pixel[CAIRO_GREEN] = (guchar) (alpha_factor * (green) + .5);	\
-		pixel[CAIRO_BLUE]  = (guchar) (alpha_factor * (blue) + .5);	\
-		pixel[CAIRO_ALPHA] = (alpha);					\
-	} while (0)
+	G_STMT_START {								\
+		gdouble factor = (gdouble) (alpha) / 0xff;			\
+		pixel[CAIRO_RED] = (guchar) (factor * (red) + .5);		\
+		pixel[CAIRO_GREEN] = (guchar) (factor * (green) + .5);		\
+		pixel[CAIRO_BLUE] = (guchar) (factor * (blue) + .5);		\
+		pixel[CAIRO_ALPHA] = alpha;					\
+	} G_STMT_END
+
+#define CAIRO_MULT(dest, src, alpha, temp)					\
+	G_STMT_START {								\
+		temp = src * alpha; 						\
+		/* approximation of division by 255 */				\
+		dest = ((temp >> 8) + temp) >> 8; 				\
+	} G_STMT_END
+
+#define CAIRO_SET_RGBA_FAST(pixel, red, green, blue, alpha, temp)		\
+	G_STMT_START {								\
+		CAIRO_MULT (pixel[CAIRO_RED], red, alpha, temp);		\
+		CAIRO_MULT (pixel[CAIRO_GREEN], green, alpha, temp);		\
+		CAIRO_MULT (pixel[CAIRO_BLUE], blue, alpha, temp);		\
+		pixel[CAIRO_ALPHA] = alpha;					\
+	} G_STMT_END
 
 #define CAIRO_GET_RGB(pixel, red, green, blue)					\
-	do {									\
-		red   = pixel[CAIRO_RED];					\
+	G_STMT_START {								\
+		red = pixel[CAIRO_RED];						\
 		green = pixel[CAIRO_GREEN];					\
-		blue   = pixel[CAIRO_BLUE];					\
-	} while (0)
+		blue = pixel[CAIRO_BLUE];					\
+	} G_STMT_END
 
 #define CAIRO_GET_RGBA(pixel, red, green, blue, alpha)				\
-	do {									\
-		gdouble alpha_factor;						\
-										\
+	G_STMT_START {								\
 		alpha = pixel[CAIRO_ALPHA];					\
-		alpha_factor = (gdouble) 0xff / alpha;		 		\
-		red   = (guchar) (pixel[CAIRO_RED] * alpha_factor + .5);	\
-		green = (guchar) (pixel[CAIRO_GREEN] * alpha_factor + .5);	\
-		blue  = (guchar) (pixel[CAIRO_BLUE] * alpha_factor + .5);	\
-	} while (0)
+		if (alpha == 0xff) {						\
+			red = pixel[CAIRO_RED];					\
+			green = pixel[CAIRO_GREEN];				\
+			blue = pixel[CAIRO_BLUE];				\
+		}								\
+		else {								\
+			gdouble factor = (gdouble) 0xff / alpha;		\
+			red = (guchar) (factor * pixel[CAIRO_RED] + .5);	\
+			green = (guchar) (factor * pixel[CAIRO_GREEN] + .5);	\
+			blue = (guchar) (factor * pixel[CAIRO_BLUE] + .5);	\
+		}								\
+	} G_STMT_END
 
 /* types */