powf4.h

Newlib 嵌入式 C库 标准实现代码

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/* PROLOG END TAG zYx                                              */
#ifdef __SPU__
#ifndef _POWF4_H_
#define _POWF4_H_	1

#include <spu_intrinsics.h>
#include <vec_types.h>

#include "exp2f4.h"
#include "log2f4.h"

/*
 * FUNCTION
 *	vector float _powf4(vector float x, vector float y)
 *
 * DESCRIPTION
 *	The _powf4 function computes x raised to the power y for the set of 
 *	vectors. The powf4 function is computed as by decomposing 
 *	the problem into:
 *
 *		x^y = 2^(y*log2(x))
 *
 */
static __inline vector float _powf4(vector float x, vector float y)
{
  vec_uint4  y_exp;
  vec_uint4  y_mantissa;
  vec_uint4  mant_shift;
  vec_uint4  y_is_int;
  vec_uint4  y_is_odd;
  vec_uint4  x_sign_bit;
  vec_uint4  zero   = (vec_uint4)spu_splats(0);
  vec_uint4  bit0   = (vec_uint4)spu_splats(0x80000000);
  vec_int4   error = spu_splats(-1);
  vec_float4 out;

  y_exp = spu_and(spu_rlmask((vec_uint4)y, -23), 0x000000FF);

  /* Need the implied bit in the mantissa to catch 
   * y = 1 case later
   */
  y_mantissa = spu_or(spu_sl((vec_uint4)y, (unsigned int)8), bit0);

  x_sign_bit = spu_and((vec_uint4)x, bit0);

  /* We are going to shift the mantissa over enough to 
   * determine if we have an integer.
   */
  mant_shift = spu_add(y_exp, -127);


  /* Leave the lowest-order integer bit of mantissa on the 
   * high end so we can see if the integer is odd.
   */
  y_mantissa  = spu_sl(y_mantissa, mant_shift);

  y_is_int = spu_cmpeq(spu_andc(y_mantissa, bit0), 0);
  y_is_int = spu_and(y_is_int, spu_cmpgt(y_exp, 126));

  y_is_odd = spu_and(spu_cmpeq(y_mantissa, bit0), y_is_int);

  out = _exp2f4(spu_mul(y, _log2f4(spu_andc(x, (vec_float4)bit0))));

  /* x < 0 is only ok when y integer 
   */
  out = spu_sel(out, (vec_float4)error, 
				  spu_andc(spu_cmpeq(x_sign_bit, bit0), y_is_int));

  /* Preserve the sign of x if y is an odd integer
   */
  out = spu_sel(out, spu_or(out, (vec_float4)x_sign_bit), y_is_odd);

  /* x = anything, y = +/- 0, returns 1
   */
  out = spu_sel(out, spu_splats(1.0f), spu_cmpabseq(y, (vec_float4)zero));

  return(out);
}

#endif /* _POWF4_H_ */
#endif /* __SPU__ */