Matcher: convert distance matrix to integer

In order to reduce the requirements on the cpu environment running
the matcher, the floating-point operations are converted to integer.
Care is taken as to not overflow the distance matrix.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>

1 files changed, 17 insertions, 4 deletions

diff --git a/src/state.c b/src/state.c
index 5387828..895d096 100644
--- a/src/state.c
+++ b/src/state.c
@@ -36,10 +36,23 @@ static int fincmp(const void *a, const void *b)
         return ((struct FingerState *)a)->id - ((struct FingerState *)b)->id;
 }
 
-inline float dist2(const struct FingerData *a, const struct FingerData *b)
+/* seander@cs.stanford.edu */
+inline unsigned abs32(int x)
 {
-        float dx = a->position_x - b->position_x;
-        float dy = a->position_y - b->position_y;
+        int const m = x >> 31;
+        return (x + m) ^ m;
+}
+
+inline int abs15(int x)
+{
+        return 32767 & abs32(x);
+}
+
+/* abslute scale is assumed to fit in 15 bits */
+inline int dist2(const struct FingerData *a, const struct FingerData *b)
+{
+        int dx = abs15(a->position_x - b->position_x);
+        int dy = abs15(a->position_y - b->position_y);
 
         return dx * dx + dy * dy;
 }
@@ -71,7 +84,7 @@ void modify_state(struct State *s,
                   const struct HWData *hw,
                   const struct Capabilities *caps)
 {
-        float A[DIM2_FINGER], *row;
+        int A[DIM2_FINGER], *row;
         int sid[DIM_FINGER], hw2s[DIM_FINGER];
         int id, sk, hwk;