drm: add some additional fixed point helpers (v3)

Required for certain driver calculations.  Code
was written by Christian König and ported to the
drm by me.

v2: fix 64 bit divides
v3: fix 64 bit for real (math64.h)

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

1 files changed, 94 insertions, 0 deletions

diff --git a/include/drm/drm_fixed.h b/include/drm/drm_fixed.h
index 0ead502e17d2..f5e1168c7647 100644
--- a/include/drm/drm_fixed.h
+++ b/include/drm/drm_fixed.h
@@ -20,10 +20,13 @@
  * OTHER DEALINGS IN THE SOFTWARE.
  *
  * Authors: Dave Airlie
+ *          Christian König
  */
 #ifndef DRM_FIXED_H
 #define DRM_FIXED_H
 
+#include <linux/math64.h>
+
 typedef union dfixed {
         u32 full;
 } fixed20_12;
@@ -65,4 +68,95 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B)
         tmp /= 2;
         return lower_32_bits(tmp);
 }
+
+#define DRM_FIXED_POINT         32
+#define DRM_FIXED_ONE           (1ULL << DRM_FIXED_POINT)
+#define DRM_FIXED_DECIMAL_MASK  (DRM_FIXED_ONE - 1)
+#define DRM_FIXED_DIGITS_MASK   (~DRM_FIXED_DECIMAL_MASK)
+
+static inline s64 drm_int2fixp(int a)
+{
+        return ((s64)a) << DRM_FIXED_POINT;
+}
+
+static inline int drm_fixp2int(int64_t a)
+{
+        return ((s64)a) >> DRM_FIXED_POINT;
+}
+
+static inline s64 drm_fixp_msbset(int64_t a)
+{
+        unsigned shift, sign = (a >> 63) & 1;
+
+        for (shift = 62; shift > 0; --shift)
+                if ((a >> shift) != sign)
+                        return shift;
+
+        return 0;
+}
+
+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;
+                b >>= shift >> 1;
+        } else
+                shift = 0;
+
+        result = a * b;
+
+        if (shift > DRM_FIXED_POINT)
+                return result << (shift - DRM_FIXED_POINT);
+
+        if (shift < DRM_FIXED_POINT)
+                return result >> (DRM_FIXED_POINT - shift);
+
+        return result;
+}
+
+static inline s64 drm_fixp_div(s64 a, s64 b)
+{
+        unsigned shift = 63 - drm_fixp_msbset(a);
+        s64 result;
+
+        a <<= shift;
+
+        if (shift < DRM_FIXED_POINT)
+                b >>= (DRM_FIXED_POINT - shift);
+
+        result = div64_s64(a, b);
+
+        if (shift > DRM_FIXED_POINT)
+                return result >> (shift - DRM_FIXED_POINT);
+
+        return result;
+}
+
+static inline s64 drm_fixp_exp(s64 x)
+{
+        s64 tolerance = div64_s64(DRM_FIXED_ONE, 1000000);
+        s64 sum = DRM_FIXED_ONE, term, y = x;
+        u64 count = 1;
+
+        if (x < 0)
+                y = -1 * x;
+
+        term = y;
+
+        while (term >= tolerance) {
+                sum = sum + term;
+                count = count + 1;
+                term = drm_fixp_mul(term, div64_s64(y, count));
+        }
+
+        if (x < 0)
+                sum = drm_fixp_div(1, sum);
+
+        return sum;
+}
+
 #endif