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/* PROLOG END TAG zYx                                              */

#ifdef __SPU__

#ifndef _EXP2F4_H_

#define _EXP2F4_H_      1

#include <spu_intrinsics.h>

#include "simdmath.h"

/*

 * FUNCTION

 *      vector float _exp2f4(vector float x)

 *

 * DESCRIPTION

 *      The _exp2f4 function computes 2 raised to the input vector x.

 *      Computation is performed by observing the 2^(a+b) = 2^a * 2^b.

 *      We decompose x into a and b (above) by letting.

 *      a = ceil(x), b = x - a;

 *

 *      2^a is easilty computed by placing a into the exponent

 *      or a floating point number whose mantissa is all zeros.

 *

 *      2^b is computed using the following polynomial approximation.

 *      (C. Hastings, Jr, 1955).

 *

 *                __7__

 *                \

 *                 \

 *      2^(-x) =   /     Ci*x^i

 *                /____

 *                 i=1

 *

 *      for x in the range 0.0 to 1.0

 *

 *      C0 =  1.0

 *      C1 = -0.9999999995

 *      C2 =  0.4999999206

 *      C3 = -0.1666653019

 *      C4 =  0.0416573475

 *      C5 = -0.0083013598

 *      C6 =  0.0013298820

 *      C7 = -0.0001413161

 *

 */

static __inline vector float _exp2f4(vector float x)

{

  vector signed int ix;

  vector unsigned int overflow, underflow;

  vector float frac, frac2, frac4;

  vector float exp_int, exp_frac;

  vector float result;

  vector float hi, lo;

  vector float bias;

  /* Break in the input x into two parts ceil(x), x - ceil(x).

   */

  bias = (vector float)(spu_rlmaska((vector signed int)(x), -31));

  bias = (vector float)(spu_andc(spu_splats((unsigned int)0x3F7FFFFF), (vector unsigned int)bias));

  ix = spu_convts(spu_add(x, bias), 0);

  frac = spu_sub(spu_convtf(ix, 0), x);

  frac = spu_mul(frac, spu_splats((float)SM_LN2));

  overflow = spu_rlmask(spu_cmpgt(ix, 128), -1);

  underflow = spu_cmpgt(ix, -128);

  exp_int = (vector float)spu_and((vector unsigned int)spu_sl(spu_add(ix, 127), 23), underflow);

  /* Instruction counts can be reduced if the polynomial was

   * computed entirely from nested (dependent) fma's. However,

   * to reduce the number of pipeline stalls, the polygon is evaluated

   * in two halves (hi amd lo).

   */

  frac2 = spu_mul(frac, frac);

  frac4 = spu_mul(frac2, frac2);

  hi = spu_madd(frac, spu_splats(-0.0001413161f), spu_splats(0.0013298820f));

  hi = spu_madd(frac, hi, spu_splats(-0.0083013598f));

  hi = spu_madd(frac, hi, spu_splats(0.0416573475f));

  lo = spu_madd(frac, spu_splats(-0.1666653019f), spu_splats(0.4999999206f));

  lo = spu_madd(frac, lo, spu_splats(-0.9999999995f));

  lo = spu_madd(frac, lo, spu_splats(1.0f));

  exp_frac = spu_madd(frac4, hi, lo);

  ix = spu_add(ix, spu_rlmask((vector signed int)(exp_frac), -23));

  result = spu_mul(exp_frac, exp_int);

  /* Handle overflow */

  result = spu_or(result, (vector float)overflow);

  return (result);

}

#endif /* _EXP2F4_H_ */

#endif /* __SPU__ */