logbf4.h

Newlib 嵌入式 C库 标准实现代码

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/* PROLOG END TAG zYx                                              */
#ifdef __SPU__

#ifndef _LOGBF4_H_
#define _LOGBF4_H_	1

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

/*
 * FUNCTION
 *	vector float _scalbnf4(vector float x, vector signed int exp)
 *
 * DESCRIPTION
 *      The _scalbnf4 function returns a vector containing each element of x 
 *      multiplied by 2^n computed efficiently.  This function is computed 
 *      without the assistance of any floating point operations and as such 
 *      does not set any floating point exceptions.
 *
 *      Special Cases:
 *	  - if the exponent is 0, then x is either 0 or a subnormal, and the 
 *          result will be returned as 0.
 *        - if the result if underflows, it will be returned as 0.
 *        - if the result overflows, it will be returned as FLT_MAX.
 *
 */
static __inline vector float _logbf4(vector float x)
{
  vec_uint4 lzero     = (vector unsigned int) {0, 0, 0, 0};
  vec_uint4 exp_mask  = (vector unsigned int) {0xFF, 0xFF, 0xFF, 0xFF};
  vec_int4  exp_shift = (vector signed int) { -23,  -23,  -23,  -23};
  vec_int4  exp_bias  = (vector signed int) {-127, -127, -127, -127};
  vec_uint4 sign_mask = (vector unsigned int) {0x80000000, 0x80000000,
		                                       0x80000000, 0x80000000};
  vec_uint4 linf      = (vector unsigned int) {0x7F800000, 0x7F800000,
		                                       0x7F800000, 0x7F800000};
  vec_uint4 lminf     = (vector unsigned int) {0xFF800000, 0xFF800000,
		                                       0xFF800000, 0xFF800000};
  vec_uint4 exp;
  vec_uint4 xabs;
  vec_float4 exp_unbias;


  xabs = spu_andc((vec_uint4)x, sign_mask);

  exp  = spu_and(spu_rlmask((vec_uint4)x, exp_shift), exp_mask);
  exp_unbias = spu_convtf(spu_add((vec_int4)exp, exp_bias), 0);

  /* Zero */
  exp_unbias = spu_sel(exp_unbias, (vec_float4)lminf, (vec_uint4)spu_cmpeq(xabs, lzero));

  /* NaN */
  exp_unbias = spu_sel(exp_unbias, x, (vec_uint4)spu_cmpgt(xabs, linf));

  /* Infinite */
  exp_unbias = spu_sel(exp_unbias, (vec_float4)linf, (vec_uint4)spu_cmpeq(xabs, linf));

  return (exp_unbias);
}

#endif /* _LOGBF4_H_ */

#endif /* __SPU__ */