powd2.h

Newlib 嵌入式 C库 标准实现代码

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/* PROLOG END TAG zYx                                              */
#ifdef __SPU__
#ifndef _POWD2_H_
#define _POWD2_H_	1

#include "exp2d2.h"
#include "log2d2.h"

/*
 * FUNCTION
 *	vector double _powd2(vector double x, vector double y)
 *
 * DESCRIPTION
 *	The _powd2 function computes x raised to the power y for the set of 
 *	vectors. The powd2 function is computed as by decomposing 
 *	the problem into:
 *
 *		x^y = 2^(y*log2(x))
 *
 *
 */
static __inline vector double _powd2(vector double x, vector double y)
{
  vec_uchar16 splat_hi = (vec_uchar16) { 0,1,2,3,0,1,2,3, 8,9,10,11, 8,9,10,11 };
  vec_int4 exp, shift;
  vec_uint4 sign = (vec_uint4) { 0x80000000, 0, 0x80000000, 0 };
  vec_uint4 or_mask, and_mask, evenmask, intmask;
  vec_double2 in_hi;
  vector double signmask = spu_splats(-0.0);
  vector signed int error = spu_splats(-1);
  vector double zero = spu_splats(0.0);
  vector unsigned int y_is_int, y_is_odd, y_is_even;
  vector unsigned int x_is_neg;
  vector double xabs, xsign;
  vector double out;


  xsign = spu_and(x, signmask);
  xabs  = spu_andc(x, signmask);
  x_is_neg = (vec_uint4)spu_cmpgt(zero, x);


  /* First we solve assuming x was non-negative */
  out = _exp2d2(spu_mul(y, _log2d2(xabs)));

  in_hi = spu_shuffle(y, y, splat_hi);
  exp = spu_and(spu_rlmask((vec_int4)in_hi, -20), 0x7FF);

  /* Determine if y is an integer */
  shift = spu_sub(((vec_int4) { 1023, 1043, 1023, 1043 }), exp);
  or_mask = spu_andc(spu_cmpgt(shift, 0), sign);
  and_mask = spu_rlmask(((vec_uint4) { 0xFFFFF, -1, 0xFFFFF, -1 }), shift);
  intmask = spu_or(spu_and(and_mask, spu_cmpgt(shift, -32)), or_mask);
  y_is_int = (vec_uint4)spu_cmpeq(y, spu_andc(y, (vec_double2)(intmask)));

  /* Determine if y is an even integer */
  shift = spu_sub(((vec_int4) { 1024, 1044, 1024, 1044 }), exp);
  or_mask = spu_andc(spu_cmpgt(shift, 0), sign);
  and_mask = spu_rlmask(((vec_uint4) { 0xFFFFF, -1, 0xFFFFF, -1 }), shift);
  evenmask = spu_or(spu_and(and_mask, spu_cmpgt(shift, -32)), or_mask);
  y_is_even = (vec_uint4)spu_cmpeq(y, spu_andc(y, (vec_double2)(evenmask)));

  y_is_odd = spu_andc(y_is_int, y_is_even);


  /* Special Cases
   */

  /* x < 0 is only ok when y integer */
  out = spu_sel(out, (vec_double2)error, (vec_ullong2)spu_andc(x_is_neg, y_is_int));

  /* Preserve the sign of x if y is an odd integer */
  out = spu_sel(out, spu_or(out, xsign), (vec_ullong2)y_is_odd);

  /* x = anything, y = +/- 0, returns 1 */
  out = spu_sel(out, spu_splats(1.0), spu_cmpabseq(y, zero));

  return(out);
}

#endif /* _POWD2_H_ */
#endif /* __SPU__ */