ps_image.cxx: better byte-swapping algorithm.

git-svn-id: file:///fltk/svn/fltk/branches/branch-1.3@7506 ea41ed52-d2ee-0310-a9c1-e6b18d33e121

1 files changed, 6 insertions, 15 deletions

diff --git a/src/ps_image.cxx b/src/ps_image.cxx
index 67d46b070..61534238c 100644
--- a/src/ps_image.cxx
+++ b/src/ps_image.cxx
@@ -182,22 +182,13 @@ int Fl_PSfile_Device::alpha_mask(const uchar * data, int w, int h, int D, int LD
   return 0;
 }
 
+// bitwise inversion of all 4-bit quantities
+static const unsigned char swapped[16] = {0,8,4,12,2,10,6,14,1,9,5,13,3,11,7,15};
 
-
-// TODO: anybody has more efficient algoritm?
-static inline uchar swap_byte(const uchar i){
-  uchar b =0;
-  if(i & 1) b |= 128;
-  if(i & 2) b |= 64;
-  if(i & 4) b |= 32;
-  if(i & 8) b |= 16;
-  if(i & 16) b |= 8;
-  if(i & 32) b |= 4;
-  if(i & 64) b |= 2;
-  if(i & 128) b |= 1;
-  return b;
-}
-
+// bitwise inversion of a byte
+static inline uchar swap_byte(const uchar b){
+ return (swapped[b & 0xF] << 4) | swapped[b >> 4];
+ }
 
 extern uchar **fl_mask_bitmap;