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Commit 64566b5e authored by Harry Wentland's avatar Harry Wentland Committed by Dave Airlie
Browse files

drm: Add drm_fixp_from_fraction and drm_fixp2int_ceil 



drm_fixp_from_fraction allows us to create a fixed point directly
from a fraction, rather than creating fixed point values and dividing
later. This avoids overflow of our 64 bit value for large numbers.

drm_fixp2int_ceil allows us to return the ceiling of our fixed point
value.

[airlied: squash Jordan's fix]
32-bit-build-fix: Jordan Lazare <Jordan.Lazare@amd.com>
Signed-off-by: default avatarHarry Wentland <harry.wentland@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Signed-off-by: default avatarDave Airlie <airlied@redhat.com>
parent 4d6a10da

include/drm/drm_fixed.h

+51 −2
Original line number Diff line number Diff line
@@ -73,18 +73,28 @@ static inline u32 dfixed_div(fixed20_12 A, fixed20_12 B) 
#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)

#define DRM_FIXED_EPSILON	1LL

#define DRM_FIXED_ALMOST_ONE	(DRM_FIXED_ONE - DRM_FIXED_EPSILON)



static inline s64 drm_int2fixp(int a)

{

	return ((s64)a) << DRM_FIXED_POINT;

}



static inline int drm_fixp2int(int64_t a)

static inline int drm_fixp2int(s64 a)

{

	return ((s64)a) >> DRM_FIXED_POINT;

}



static inline unsigned drm_fixp_msbset(int64_t a)

static inline int drm_fixp2int_ceil(s64 a)

{

	if (a > 0)

		return drm_fixp2int(a + DRM_FIXED_ALMOST_ONE);

	else

		return drm_fixp2int(a - DRM_FIXED_ALMOST_ONE);

}



static inline unsigned drm_fixp_msbset(s64 a)

{

	unsigned shift, sign = (a >> 63) & 1;
@@ -136,6 +146,45 @@ static inline s64 drm_fixp_div(s64 a, s64 b) 
	return result;

}



static inline s64 drm_fixp_from_fraction(s64 a, s64 b)

{

	s64 res;

	bool a_neg = a < 0;

	bool b_neg = b < 0;

	u64 a_abs = a_neg ? -a : a;

	u64 b_abs = b_neg ? -b : b;

	u64 rem;



	/* determine integer part */

	u64 res_abs  = div64_u64_rem(a_abs, b_abs, &rem);



	/* determine fractional part */

	{

		u32 i = DRM_FIXED_POINT;



		do {

			rem <<= 1;

			res_abs <<= 1;

			if (rem >= b_abs) {

				res_abs |= 1;

				rem -= b_abs;

			}

		} while (--i != 0);

	}



	/* round up LSB */

	{

		u64 summand = (rem << 1) >= b_abs;



		res_abs += summand;

	}



	res = (s64) res_abs;

	if (a_neg ^ b_neg)

		res = -res;

	return res;

}



static inline s64 drm_fixp_exp(s64 x)

{

	s64 tolerance = div64_s64(DRM_FIXED_ONE, 1000000);