drm: fix 64 bit drm fixed point helpers

Sign bit wasn't handled properly and a small typo.

Thanks to Christian for helping me sort this out.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
index f5e1168c76473d3c1180cbcac654eac67ee2373f..d639049a613dfdb264650f8ee938836e6ed28e10 100644 (file)
--- a/include/drm/drm_fixed.h
+++ b/include/drm/drm_fixed.h
@@ -84,12 +84,12 @@ static inline int drm_fixp2int(int64_t a)
        return ((s64)a) >> DRM_FIXED_POINT;
 }
 
-static inline s64 drm_fixp_msbset(int64_t a)
+static inline unsigned drm_fixp_msbset(int64_t a)
 {
        unsigned shift, sign = (a >> 63) & 1;
 
        for (shift = 62; shift > 0; --shift)
-               if ((a >> shift) != sign)
+               if (((a >> shift) & 1) != sign)
                        return shift;
 
        return 0;
@@ -100,9 +100,9 @@ static inline s64 drm_fixp_mul(s64 a, s64 b)
        unsigned shift = drm_fixp_msbset(a) + drm_fixp_msbset(b);
        s64 result;
 
-       if (shift > 63) {
-               shift = shift - 63;
-               a >>= shift >> 1;
+       if (shift > 61) {
+               shift = shift - 61;
+               a >>= (shift >> 1) + (shift & 1);
                b >>= shift >> 1;
        } else
                shift = 0;
@@ -120,7 +120,7 @@ static inline s64 drm_fixp_mul(s64 a, s64 b)
 
 static inline s64 drm_fixp_div(s64 a, s64 b)
 {
-       unsigned shift = 63 - drm_fixp_msbset(a);
+       unsigned shift = 62 - drm_fixp_msbset(a);
        s64 result;
 
        a <<= shift;
@@ -154,7 +154,7 @@ static inline s64 drm_fixp_exp(s64 x)
        }
 
        if (x < 0)
-               sum = drm_fixp_div(1, sum);
+               sum = drm_fixp_div(DRM_FIXED_ONE, sum);
 
        return sum;
 }