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[base] Clean up trigonometric core.

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* src/base/fttrigon.c: Document the algorithm in a large comment.
(FT_TRIG_COSCALE): Remove macro.
(FT_Tan: Use `FT_TRIG_SCALE' instead.
(FT_Cos, FT_Vector_Unit): Ditto and round the return values.
This commit is contained in:
Alexei Podtelezhnikov 2013-01-08 23:29:44 -05:00
parent 5dd9657fe8
commit 09dbb059e1
2 changed files with 28 additions and 9 deletions
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9
ChangeLog
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@ -1,3 +1,12 @@
2013-01-08 Alexei Podtelezhnikov <apodtele@gmail.com>
[base] Clean up trigonometric core.
* src/base/fttrigon.c: Document the algorithm in a large comment.
(FT_TRIG_COSCALE): Remove macro.
(FT_Tan: Use `FT_TRIG_SCALE' instead.
(FT_Cos, FT_Vector_Unit): Ditto and round the return values.
2013-01-02 Alexei Podtelezhnikov <apodtele@gmail.com>
[base] Use rounding in CORDIC iterations.

28
src/base/fttrigon.c
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@ -15,6 +15,19 @@
/* */
/***************************************************************************/
/*************************************************************************/
/* */
/* This is a fixed-point CORDIC implementation of trigonometric */
/* functions as well as transformations between Cartesian and polar */
/* coordinates. The angles are represented as a 16.16 fixed-point value */
/* in degrees, i.e., the angular resolution is 2^-16 degrees. Note that */
/* only vectors longer than 2^16*180/pi (or at least 22 bits) on a */
/* discrete Cartesian greed can have the same or better angular */
/* resolution. Therefore, to maintain this precision, some functions */
/* require the interim upscaling of the vectors, whereas others operate */
/* with 24-bit long vectors from the start. */
/* */
/*************************************************************************/
#include <ft2build.h>
#include FT_INTERNAL_OBJECTS_H
@ -29,9 +42,6 @@
/* the Cordic shrink factor 0.858785336480436 * 2^32 */
#define FT_TRIG_SCALE 0xDBD95B16UL
/* the following is 0.858785336480436 * 2^30 */
#define FT_TRIG_COSCALE 0x36F656C6UL
/* this table was generated for FT_PI = 180L << 16, i.e. degrees */
#define FT_TRIG_MAX_ITERS 23
@ -326,11 +336,11 @@
FT_Vector v;
v.x = FT_TRIG_COSCALE >> 2;
v.x = FT_TRIG_SCALE >> 8;
v.y = 0;
ft_trig_pseudo_rotate( &v, angle );
return v.x / ( 1 << 12 );
return ( v.x + 0x80L ) >> 8;
}
@ -351,7 +361,7 @@
FT_Vector v;
v.x = FT_TRIG_COSCALE >> 2;
v.x = FT_TRIG_SCALE >> 8;
v.y = 0;
ft_trig_pseudo_rotate( &v, angle );
@ -386,11 +396,11 @@
FT_Vector_Unit( FT_Vector* vec,
FT_Angle angle )
{
vec->x = FT_TRIG_COSCALE >> 2;
vec->x = FT_TRIG_SCALE >> 8;
vec->y = 0;
ft_trig_pseudo_rotate( vec, angle );
vec->x >>= 12;
vec->y >>= 12;
vec->x = ( vec->x + 0x80L ) >> 8;
vec->y = ( vec->y + 0x80L ) >> 8;
}