ref: e9c50fa77de58b749b4b95706f7b55bfff0dd27f
dir: /src/base/fttrigon.c/
/****************************************************************************
*
* fttrigon.c
*
* FreeType trigonometric functions (body).
*
* Copyright (C) 2001-2021 by
* David Turner, Robert Wilhelm, and Werner Lemberg.
*
* This file is part of the FreeType project, and may only be used,
* modified, and distributed under the terms of the FreeType project
* license, LICENSE.TXT. By continuing to use, modify, or distribute
* this file you indicate that you have read the license and
* understand and accept it fully.
*
*/
/**************************************************************************
*
* This is a fixed-point CORDIC implementation of trigonometric
* functions as well as transformations between Cartesian and polar
* coordinates. The angles are represented as 16.16 fixed-point values
* 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 grid can have the same or better angular
* resolution. Therefore, to maintain this precision, some functions
* require an interim upscaling of the vectors, whereas others operate
* with 24-bit long vectors directly.
*
*/
#include <freetype/internal/ftobjs.h>
#include <freetype/internal/ftcalc.h>
#include <freetype/fttrigon.h>
/* the Cordic shrink factor 0.858785336480436 * 2^32 */
#define FT_TRIG_SCALE 0xDBD95B16UL
/* the highest bit in overflow-safe vector components, */
/* MSB of 0.858785336480436 * sqrt(0.5) * 2^30 */
#define FT_TRIG_SAFE_MSB 29
/* this table was generated for FT_PI = 180L << 16, i.e. degrees */
#define FT_TRIG_MAX_ITERS 23
static const FT_Angle
ft_trig_arctan_table[] =
{
1740967L, 919879L, 466945L, 234379L, 117304L, 58666L, 29335L,
14668L, 7334L, 3667L, 1833L, 917L, 458L, 229L, 115L,
57L, 29L, 14L, 7L, 4L, 2L, 1L
};
#ifdef FT_LONG64
/* multiply a given value by the CORDIC shrink factor */
static FT_Fixed
ft_trig_downscale( FT_Fixed val )
{
FT_Int s = 1;
if ( val < 0 )
{
val = -val;
s = -1;
}
/* 0x40000000 comes from regression analysis between true */
/* and CORDIC hypotenuse, so it minimizes the error */
val = (FT_Fixed)(
( (FT_UInt64)val * FT_TRIG_SCALE + 0x40000000UL ) >> 32 );
return s < 0 ? -val : val;
}
#else /* !FT_LONG64 */
/* multiply a given value by the CORDIC shrink factor */
static FT_Fixed
ft_trig_downscale( FT_Fixed val )
{
FT_Int s = 1;
FT_UInt32 lo1, hi1, lo2, hi2, lo, hi, i1, i2;
if ( val < 0 )
{
val = -val;
s = -1;
}
lo1 = (FT_UInt32)val & 0x0000FFFFU;
hi1 = (FT_UInt32)val >> 16;
lo2 = FT_TRIG_SCALE & 0x0000FFFFU;
hi2 = FT_TRIG_SCALE >> 16;
lo = lo1 * lo2;
i1 = lo1 * hi2;
i2 = lo2 * hi1;
hi = hi1 * hi2;
/* Check carry overflow of i1 + i2 */
i1 += i2;
hi += (FT_UInt32)( i1 < i2 ) << 16;
hi += i1 >> 16;
i1 = i1 << 16;
/* Check carry overflow of i1 + lo */
lo += i1;
hi += ( lo < i1 );
/* 0x40000000 comes from regression analysis between true */
/* and CORDIC hypotenuse, so it minimizes the error */
/* Check carry overflow of lo + 0x40000000 */
lo += 0x40000000UL;
hi += ( lo < 0x40000000UL );
val = (FT_Fixed)hi;
return s < 0 ? -val : val;
}
#endif /* !FT_LONG64 */
/* undefined and never called for zero vector */
static FT_Int
ft_trig_prenorm( FT_Vector* vec )
{
FT_Pos x, y;
FT_Int shift;
x = vec->x;
y = vec->y;
shift = FT_MSB( (FT_UInt32)( FT_ABS( x ) | FT_ABS( y ) ) );
if ( shift <= FT_TRIG_SAFE_MSB )
{
shift = FT_TRIG_SAFE_MSB - shift;
vec->x = (FT_Pos)( (FT_ULong)x << shift );
vec->y = (FT_Pos)( (FT_ULong)y << shift );
}
else
{
shift -= FT_TRIG_SAFE_MSB;
vec->x = x >> shift;
vec->y = y >> shift;
shift = -shift;
}
return shift;
}
static void
ft_trig_pseudo_rotate( FT_Vector* vec,
FT_Angle theta )
{
FT_Int i;
FT_Fixed x, y, xtemp, b;
const FT_Angle *arctanptr;
x = vec->x;
y = vec->y;
/* Rotate inside [-PI/4,PI/4] sector */
while ( theta < -FT_ANGLE_PI4 )
{
xtemp = y;
y = -x;
x = xtemp;
theta += FT_ANGLE_PI2;
}
while ( theta > FT_ANGLE_PI4 )
{
xtemp = -y;
y = x;
x = xtemp;
theta -= FT_ANGLE_PI2;
}
arctanptr = ft_trig_arctan_table;
/* Pseudorotations, with right shifts */
for ( i = 1, b = 1; i < FT_TRIG_MAX_ITERS; b <<= 1, i++ )
{
if ( theta < 0 )
{
xtemp = x + ( ( y + b ) >> i );
y = y - ( ( x + b ) >> i );
x = xtemp;
theta += *arctanptr++;
}
else
{
xtemp = x - ( ( y + b ) >> i );
y = y + ( ( x + b ) >> i );
x = xtemp;
theta -= *arctanptr++;
}
}
vec->x = x;
vec->y = y;
}
static void
ft_trig_pseudo_polarize( FT_Vector* vec )
{
FT_Angle theta;
FT_Int i;
FT_Fixed x, y, xtemp, b;
const FT_Angle *arctanptr;
x = vec->x;
y = vec->y;
/* Get the vector into [-PI/4,PI/4] sector */
if ( y > x )
{
if ( y > -x )
{
theta = FT_ANGLE_PI2;
xtemp = y;
y = -x;
x = xtemp;
}
else
{
theta = y > 0 ? FT_ANGLE_PI : -FT_ANGLE_PI;
x = -x;
y = -y;
}
}
else
{
if ( y < -x )
{
theta = -FT_ANGLE_PI2;
xtemp = -y;
y = x;
x = xtemp;
}
else
{
theta = 0;
}
}
arctanptr = ft_trig_arctan_table;
/* Pseudorotations, with right shifts */
for ( i = 1, b = 1; i < FT_TRIG_MAX_ITERS; b <<= 1, i++ )
{
if ( y > 0 )
{
xtemp = x + ( ( y + b ) >> i );
y = y - ( ( x + b ) >> i );
x = xtemp;
theta += *arctanptr++;
}
else
{
xtemp = x - ( ( y + b ) >> i );
y = y + ( ( x + b ) >> i );
x = xtemp;
theta -= *arctanptr++;
}
}
/* round theta to acknowledge its error that mostly comes */
/* from accumulated rounding errors in the arctan table */
if ( theta >= 0 )
theta = FT_PAD_ROUND( theta, 16 );
else
theta = -FT_PAD_ROUND( -theta, 16 );
vec->x = x;
vec->y = theta;
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( FT_Fixed )
FT_Cos( FT_Angle angle )
{
FT_Vector v;
FT_Vector_Unit( &v, angle );
return v.x;
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( FT_Fixed )
FT_Sin( FT_Angle angle )
{
FT_Vector v;
FT_Vector_Unit( &v, angle );
return v.y;
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( FT_Fixed )
FT_Tan( FT_Angle angle )
{
FT_Vector v = { 1 << 24, 0 };
ft_trig_pseudo_rotate( &v, angle );
return FT_DivFix( v.y, v.x );
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( FT_Angle )
FT_Atan2( FT_Fixed dx,
FT_Fixed dy )
{
FT_Vector v;
if ( dx == 0 && dy == 0 )
return 0;
v.x = dx;
v.y = dy;
ft_trig_prenorm( &v );
ft_trig_pseudo_polarize( &v );
return v.y;
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( void )
FT_Vector_Unit( FT_Vector* vec,
FT_Angle angle )
{
if ( !vec )
return;
vec->x = FT_TRIG_SCALE >> 8;
vec->y = 0;
ft_trig_pseudo_rotate( vec, angle );
vec->x = ( vec->x + 0x80L ) >> 8;
vec->y = ( vec->y + 0x80L ) >> 8;
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( void )
FT_Vector_Rotate( FT_Vector* vec,
FT_Angle angle )
{
FT_Int shift;
FT_Vector v;
if ( !vec || !angle )
return;
v = *vec;
if ( v.x == 0 && v.y == 0 )
return;
shift = ft_trig_prenorm( &v );
ft_trig_pseudo_rotate( &v, angle );
v.x = ft_trig_downscale( v.x );
v.y = ft_trig_downscale( v.y );
if ( shift > 0 )
{
FT_Int32 half = (FT_Int32)1L << ( shift - 1 );
vec->x = ( v.x + half - ( v.x < 0 ) ) >> shift;
vec->y = ( v.y + half - ( v.y < 0 ) ) >> shift;
}
else
{
shift = -shift;
vec->x = (FT_Pos)( (FT_ULong)v.x << shift );
vec->y = (FT_Pos)( (FT_ULong)v.y << shift );
}
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( FT_Fixed )
FT_Vector_Length( FT_Vector* vec )
{
FT_Int shift;
FT_Vector v;
if ( !vec )
return 0;
v = *vec;
/* handle trivial cases */
if ( v.x == 0 )
{
return FT_ABS( v.y );
}
else if ( v.y == 0 )
{
return FT_ABS( v.x );
}
/* general case */
shift = ft_trig_prenorm( &v );
ft_trig_pseudo_polarize( &v );
v.x = ft_trig_downscale( v.x );
if ( shift > 0 )
return ( v.x + ( 1L << ( shift - 1 ) ) ) >> shift;
return (FT_Fixed)( (FT_UInt32)v.x << -shift );
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( void )
FT_Vector_Polarize( FT_Vector* vec,
FT_Fixed *length,
FT_Angle *angle )
{
FT_Int shift;
FT_Vector v;
if ( !vec || !length || !angle )
return;
v = *vec;
if ( v.x == 0 && v.y == 0 )
return;
shift = ft_trig_prenorm( &v );
ft_trig_pseudo_polarize( &v );
v.x = ft_trig_downscale( v.x );
*length = shift >= 0 ? ( v.x >> shift )
: (FT_Fixed)( (FT_UInt32)v.x << -shift );
*angle = v.y;
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( void )
FT_Vector_From_Polar( FT_Vector* vec,
FT_Fixed length,
FT_Angle angle )
{
if ( !vec )
return;
vec->x = length;
vec->y = 0;
FT_Vector_Rotate( vec, angle );
}
/* documentation is in fttrigon.h */
FT_EXPORT_DEF( FT_Angle )
FT_Angle_Diff( FT_Angle angle1,
FT_Angle angle2 )
{
FT_Angle delta = angle2 - angle1;
while ( delta <= -FT_ANGLE_PI )
delta += FT_ANGLE_2PI;
while ( delta > FT_ANGLE_PI )
delta -= FT_ANGLE_2PI;
return delta;
}
/* END */