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avfilter/vf_rotate: increase fixed point precision

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This ensures int_sins output doesnt have "random" lsbs

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer
2014-04-19 00:29:57 +02:00
parent 3a1feb01da
commit a47cc877a0
2 changed files with 29 additions and 28 deletions
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17
libavfilter/vf_rotate.c
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@@ -252,11 +252,12 @@ static int config_props(AVFilterLink *outlink)
}
#define FIXP (1<<16)
#define INT_PI 205887 //(M_PI * FIXP)
#define FIXP2 (1<<20)
#define INT_PI 3294199 //(M_PI * FIXP2)
/**
* Compute the sin of a using integer values.
* Input and output values are scaled by FIXP.
* Input is scaled by FIXP2 and output values are scaled by FIXP.
*/
static int64_t int_sin(int64_t a)
{
@@ -268,13 +269,13 @@ static int64_t int_sin(int64_t a)
if (a >= INT_PI*3/2) a -= 2*INT_PI; // -PI/2 .. 3PI/2
if (a >= INT_PI/2 ) a = INT_PI - a; // -PI/2 .. PI/2
/* compute sin using Taylor series approximated to the third term */
a2 = (a*a)/FIXP;
for (i = 2; i < 7; i += 2) {
/* compute sin using Taylor series approximated to the fifth term */
a2 = (a*a)/(FIXP2);
for (i = 2; i < 11; i += 2) {
res += a;
a = -a*a2 / (FIXP*i*(i+1));
a = -a*a2 / (FIXP2*i*(i+1));
}
return res;
return (res + 8)>>4;
}
/**
@@ -402,7 +403,7 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *in)
av_log(ctx, AV_LOG_DEBUG, "n:%f time:%f angle:%f/PI\n",
rot->var_values[VAR_N], rot->var_values[VAR_T], rot->angle/M_PI);
angle_int = res * FIXP;
angle_int = res * FIXP * 16;
s = int_sin(angle_int);
c = int_sin(angle_int + INT_PI/2);