asinf4.h

Newlib 嵌入式 C库 标准实现代码

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#ifdef __SPU__

#ifndef _ASINF4_H_
#define _ASINF4_H_	1

#include <spu_intrinsics.h>

#include "divf4.h"
#include "sqrtf4.h"

/*
 * FUNCTION
 *	vector float _asinf4(vector float x)
 *
 * DESCRIPTION
 *	The _asinf4 function computes the arc sine for a vector of values x; 
 *      that is the values whose sine is x. Results are undefined if x is 
 *      outside the range [-1, 1]. 
 *
 */
static __inline vector float _asinf4(vector float x)
{
  /* The arcsin is computed using two different algorithms, depending
   * upon the absolute value of the input. For inputs in the range 
   * [0, PI/4], it is computed as the ratio of two polynomials.
   *
   *	asin(x) = p/q;
   *
   *    where p = P11*x^11 + P09*x^9 + P07*x^7 + P05*x^5 + P03*x3 + x
   *          q = Q08*x^8  + Q06*x^6 + Q04*x^4 + Q02*x^2 + Q00
   *
   * For the range of value [PI/4, 1], the arcsin is computed using:
   *
   *    asin = PI/2 - sqrt(1 - x) * r;
   *
   *    where r = C07*x^7 + C06*x^6 + C05*x^5 + C04*x^4 + C03*x^3 + C02*x^2
   *              C01*x   + C00;
   */
  vector float r, r1, r2, r_hi, r_lo;
  vector float xabs, x2, x4, x6;
  vector float p, p_hi, p_lo;
  vector float q, q_hi, q_lo;
  vector float pi_over_2 = spu_splats(1.5707963267949f);
  vector float pi_over_4 = spu_splats(0.7853981633974f);
  vector unsigned int msb = spu_splats(0x80000000);


  x2 = spu_mul(x, x);
  x4 = spu_mul(x2, x2);
  x6 = spu_mul(x4, x2);

  xabs = spu_andc(x, (vector float)msb);

  /* Compute arc-sin for values in the range [0, PI/4]
   */
  p_hi = spu_madd(spu_splats(0.0000347933107596021167570f), x2,
		  spu_splats(0.000791534994289814532176f));
  p_hi = spu_madd(p_hi, x2, spu_splats(-0.0400555345006794114027f));

  p_lo = spu_madd(spu_splats(0.201212532134862925881f), x2,
		  spu_splats(-0.325565818622400915405f));
  p_lo = spu_madd(p_lo, x2, spu_splats(0.166666666666666657415f));
  
  p = spu_madd(p_hi, x6, p_lo);

  q_hi = spu_madd(spu_splats(0.0770381505559019352791f), x2,
		  spu_splats(-0.688283971605453293030f));
  q_hi = spu_madd(q_hi, x2, spu_splats(2.02094576023350569471f));

  q_lo = spu_madd(spu_splats(-2.40339491173441421878f), x2, 
		  spu_splats(1.0f));

  q = spu_madd(q_hi, x4, q_lo);

  r1 = spu_madd(_divf4(p, q), spu_mul(xabs, x2), xabs);

  /* Compute arc-sin for values in the range [PI/4, 1]
   */
  r_hi = spu_madd(spu_splats(-0.0012624911f), xabs,
		  spu_splats(0.0066700901f));
  r_hi = spu_madd(r_hi, xabs, spu_splats(-0.0170881256f));
  r_hi = spu_madd(r_hi, xabs, spu_splats(0.0308918810f));

  r_lo = spu_madd(spu_splats(-0.0501743046f), xabs,
		  spu_splats(0.0889789874f));
  r_lo = spu_madd(r_lo, xabs, spu_splats(-0.2145988016f));
  r_lo = spu_madd(r_lo, xabs, pi_over_2);

  r = spu_madd(r_hi, x4, r_lo);
  
  r2 = spu_nmsub(r, _sqrtf4(spu_sub(spu_splats(1.0f), xabs)), 
		 pi_over_2);

  /* Select the result depending upon the input value. Correct the
   * sign of the result.
   */
  return (spu_sel(spu_sel(r1, r2, spu_cmpgt(xabs, pi_over_4)), 
		  x, msb));
}

#endif /* _ASINF4_H_ */
#endif /* __SPU__ */