[PATCH 1/3] fixp-arith: replace sin/cos table by a better precision one

[Hans Verkuil <hverkuil@xs4all.nl>]

From: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

The cos table used at fixp-arith.h has only 8 bits of precision.
That causes problems if it is reused on other drivers.

As some media drivers require a higher precision sin/cos
implementation, replace the current implementation by one that
will provide 32 bits precision.

The values generated by the new implementation matches the
32 bit precision of glibc's sin for an angle measured in
integer degrees.

It also provides support for fractional angles via linear
interpolation. On experimental calculus, when used a table
with a 0.001 degree angle, the maximum error for sin is
0.000038, which is likely good enough for practical purposes.

There are some logic there that seems to be specific to the
usage inside ff-memless.c. Move those logic to there, as they're
not needed elsewhere.

Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org <linux-input@vger.kernel.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
Signed-off-by: Prashant Laddha <prladdha@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
---
 drivers/input/ff-memless.c      |  18 ++++-
 drivers/media/usb/gspca/ov534.c |  11 +--
 include/linux/fixp-arith.h      | 145 +++++++++++++++++++++++++++++-----------
 3 files changed, 125 insertions(+), 49 deletions(-)

diff --git a/drivers/input/ff-memless.c b/drivers/input/ff-memless.c
index 74c0d8c..fcc6c33 100644
--- a/drivers/input/ff-memless.c
+++ b/drivers/input/ff-memless.c
@@ -237,6 +237,18 @@ static u16 ml_calculate_direction(u16 direction, u16 force,
 		(force + new_force)) << 1;
 }
 
+#define FRAC_N 8
+static inline s16 fixp_new16(s16 a)
+{
+	return ((s32)a) >> (16 - FRAC_N);
+}
+
+static inline s16 fixp_mult(s16 a, s16 b)
+{
+	a = ((s32)a * 0x100) / 0x7fff;
+	return ((s32)(a * b)) >> FRAC_N;
+}
+
 /*
  * Combine two effects and apply gain.
  */
@@ -247,7 +259,7 @@ static void ml_combine_effects(struct ff_effect *effect,
 	struct ff_effect *new = state->effect;
 	unsigned int strong, weak, i;
 	int x, y;
-	fixp_t level;
+	s16 level;
 
 	switch (new->type) {
 	case FF_CONSTANT:
@@ -255,8 +267,8 @@ static void ml_combine_effects(struct ff_effect *effect,
 		level = fixp_new16(apply_envelope(state,
 					new->u.constant.level,
 					&new->u.constant.envelope));
-		x = fixp_mult(fixp_sin(i), level) * gain / 0xffff;
-		y = fixp_mult(-fixp_cos(i), level) * gain / 0xffff;
+		x = fixp_mult(fixp_sin16(i), level) * gain / 0xffff;
+		y = fixp_mult(-fixp_cos16(i), level) * gain / 0xffff;
 		/*
 		 * here we abuse ff_ramp to hold x and y of constant force
 		 * If in future any driver wants something else than x and y
diff --git a/drivers/media/usb/gspca/ov534.c b/drivers/media/usb/gspca/ov534.c
index a9c866d..146071b 100644
--- a/drivers/media/usb/gspca/ov534.c
+++ b/drivers/media/usb/gspca/ov534.c
@@ -816,21 +816,16 @@ static void sethue(struct gspca_dev *gspca_dev, s32 val)
 		s16 huesin;
 		s16 huecos;
 
-		/* fixp_sin and fixp_cos accept only positive values, while
-		 * our val is between -90 and 90
-		 */
-		val += 360;
-
 		/* According to the datasheet the registers expect HUESIN and
 		 * HUECOS to be the result of the trigonometric functions,
 		 * scaled by 0x80.
 		 *
-		 * The 0x100 here represents the maximun absolute value
+		 * The 0x7fff here represents the maximum absolute value
 		 * returned byt fixp_sin and fixp_cos, so the scaling will
 		 * consider the result like in the interval [-1.0, 1.0].
 		 */
-		huesin = fixp_sin(val) * 0x80 / 0x100;
-		huecos = fixp_cos(val) * 0x80 / 0x100;
+		huesin = fixp_sin16(val) * 0x80 / 0x7fff;
+		huecos = fixp_cos16(val) * 0x80 / 0x7fff;
 
 		if (huesin < 0) {
 			sccb_reg_write(gspca_dev, 0xab,
diff --git a/include/linux/fixp-arith.h b/include/linux/fixp-arith.h
index 3089d73..d4686fe 100644
--- a/include/linux/fixp-arith.h
+++ b/include/linux/fixp-arith.h
@@ -1,6 +1,8 @@
 #ifndef _FIXP_ARITH_H
 #define _FIXP_ARITH_H
 
+#include <linux/math64.h>
+
 /*
  * Simplistic fixed-point arithmetics.
  * Hmm, I'm probably duplicating some code :(
@@ -29,59 +31,126 @@
 
 #include <linux/types.h>
 
-/* The type representing fixed-point values */
-typedef s16 fixp_t;
+static const s32 sin_table[] = {
+	0x00000000, 0x023be165, 0x04779632, 0x06b2f1d2, 0x08edc7b6, 0x0b27eb5c,
+	0x0d61304d, 0x0f996a26, 0x11d06c96, 0x14060b67, 0x163a1a7d, 0x186c6ddd,
+	0x1a9cd9ac, 0x1ccb3236, 0x1ef74bf2, 0x2120fb82, 0x234815ba, 0x256c6f9e,
+	0x278dde6e, 0x29ac379f, 0x2bc750e8, 0x2ddf003f, 0x2ff31bdd, 0x32037a44,
+	0x340ff241, 0x36185aee, 0x381c8bb5, 0x3a1c5c56, 0x3c17a4e7, 0x3e0e3ddb,
+	0x3fffffff, 0x41ecc483, 0x43d464fa, 0x45b6bb5d, 0x4793a20f, 0x496af3e1,
+	0x4b3c8c11, 0x4d084650, 0x4ecdfec6, 0x508d9210, 0x5246dd48, 0x53f9be04,
+	0x55a6125a, 0x574bb8e5, 0x58ea90c2, 0x5a827999, 0x5c135399, 0x5d9cff82,
+	0x5f1f5ea0, 0x609a52d1, 0x620dbe8a, 0x637984d3, 0x64dd894f, 0x6639b039,
+	0x678dde6d, 0x68d9f963, 0x6a1de735, 0x6b598ea1, 0x6c8cd70a, 0x6db7a879,
+	0x6ed9eba0, 0x6ff389de, 0x71046d3c, 0x720c8074, 0x730baeec, 0x7401e4bf,
+	0x74ef0ebb, 0x75d31a5f, 0x76adf5e5, 0x777f903b, 0x7847d908, 0x7906c0af,
+	0x79bc384c, 0x7a6831b8, 0x7b0a9f8c, 0x7ba3751c, 0x7c32a67c, 0x7cb82884,
+	0x7d33f0c8, 0x7da5f5a3, 0x7e0e2e31, 0x7e6c924f, 0x7ec11aa3, 0x7f0bc095,
+	0x7f4c7e52, 0x7f834ecf, 0x7fb02dc4, 0x7fd317b3, 0x7fec09e1, 0x7ffb025e,
+	0x7fffffff
+};
 
-#define FRAC_N 8
-#define FRAC_MASK ((1<<FRAC_N)-1)
+/**
+ * __fixp_sin32() returns the sin of an angle in degrees
+ *
+ * @degrees: angle, in degrees, from 0 to 360.
+ *
+ * The returned value ranges from -0x7fffffff to +0x7fffffff.
+ */
+static inline s32 __fixp_sin32(int degrees)
+{
+	s32 ret;
+	bool negative = false;
 
-/* Not to be used directly. Use fixp_{cos,sin} */
-static const fixp_t cos_table[46] = {
-	0x0100,	0x00FF,	0x00FF,	0x00FE,	0x00FD,	0x00FC,	0x00FA,	0x00F8,
-	0x00F6,	0x00F3,	0x00F0,	0x00ED,	0x00E9,	0x00E6,	0x00E2,	0x00DD,
-	0x00D9,	0x00D4,	0x00CF,	0x00C9,	0x00C4,	0x00BE,	0x00B8,	0x00B1,
-	0x00AB,	0x00A4,	0x009D,	0x0096,	0x008F,	0x0087,	0x0080,	0x0078,
-	0x0070,	0x0068,	0x005F,	0x0057,	0x004F,	0x0046,	0x003D,	0x0035,
-	0x002C,	0x0023,	0x001A,	0x0011,	0x0008, 0x0000
-};
+	if (degrees > 180) {
+		negative = true;
+		degrees -= 180;
+	}
+	if (degrees > 90)
+		degrees = 180 - degrees;
 
+	ret = sin_table[degrees];
 
-/* a: 123 -> 123.0 */
-static inline fixp_t fixp_new(s16 a)
-{
-	return a<<FRAC_N;
+	return negative ? -ret : ret;
 }
 
-/* a: 0xFFFF -> -1.0
-      0x8000 -> 1.0
-      0x0000 -> 0.0
-*/
-static inline fixp_t fixp_new16(s16 a)
+/**
+ * fixp_sin32() returns the sin of an angle in degrees
+ *
+ * @degrees: angle, in degrees. The angle can be positive or negative
+ *
+ * The returned value ranges from -0x7fffffff to +0x7fffffff.
+ */
+static inline s32 fixp_sin32(int degrees)
 {
-	return ((s32)a)>>(16-FRAC_N);
+	degrees = (degrees % 360 + 360) % 360;
+
+	return __fixp_sin32(degrees);
 }
 
-static inline fixp_t fixp_cos(unsigned int degrees)
+/* cos(x) = sin(x + 90 degrees) */
+#define fixp_cos32(v) fixp_sin32((v) + 90)
+
+/*
+ * 16 bits variants
+ *
+ * The returned value ranges from -0x7fff to 0x7fff
+ */
+
+#define fixp_sin16(v) (fixp_sin32(v) >> 16)
+#define fixp_cos16(v) (fixp_cos32(v) >> 16)
+
+/**
+ * fixp_sin32_rad() - calculates the sin of an angle in radians
+ *
+ * @radians: angle, in radians
+ * @twopi: value to be used for 2*pi
+ *
+ * Provides a variant for the cases where just 360
+ * values is not enough. This function uses linear
+ * interpolation to a wider range of values given by
+ * twopi var.
+ *
+ * Experimental tests gave a maximum difference of
+ * 0.000038 between the value calculated by sin() and
+ * the one produced by this function, when twopi is
+ * equal to 360000. That seems to be enough precision
+ * for practical purposes.
+ *
+ * Please notice that two high numbers for twopi could cause
+ * overflows, so the routine will not allow values of twopi
+ * bigger than 1^18.
+ */
+static inline s32 fixp_sin32_rad(u32 radians, u32 twopi)
 {
-	int quadrant = (degrees / 90) & 3;
-	unsigned int i = degrees % 90;
+	int degrees;
+	s32 v1, v2, dx, dy;
+	s64 tmp;
 
-	if (quadrant == 1 || quadrant == 3)
-		i = 90 - i;
+	/*
+	 * Avoid too large values for twopi, as we don't want overflows.
+	 */
+	BUG_ON(twopi > 1 << 18);
 
-	i >>= 1;
+	degrees = (radians * 360) / twopi;
+	tmp = radians - (degrees * twopi) / 360;
 
-	return (quadrant == 1 || quadrant == 2)? -cos_table[i] : cos_table[i];
-}
+	degrees = (degrees % 360 + 360) % 360;
+	v1 = __fixp_sin32(degrees);
 
-static inline fixp_t fixp_sin(unsigned int degrees)
-{
-	return -fixp_cos(degrees + 90);
-}
+	v2 = fixp_sin32(degrees + 1);
 
-static inline fixp_t fixp_mult(fixp_t a, fixp_t b)
-{
-	return ((s32)(a*b))>>FRAC_N;
+	dx = twopi / 360;
+	dy = v2 - v1;
+
+	tmp *= dy;
+
+	return v1 +  div_s64(tmp, dx);
 }
 
+/* cos(x) = sin(x + pi/2 radians) */
+
+#define fixp_cos32_rad(rad, twopi)	\
+	fixp_sin32_rad(rad + twopi / 4, twopi)
+
 #endif
-- 
2.1.4