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[/] [openrisc/] [trunk/] [gnu-src/] [newlib-1.18.0/] [newlib/] [libm/] [machine/] [spu/] [headers/] [log2f.h] - Blame information for rev 207

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1 207 jeremybenn
/*
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  (C) Copyright 2001,2006,
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  International Business Machines Corporation,
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  Sony Computer Entertainment, Incorporated,
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  Toshiba Corporation,
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  All rights reserved.
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  Redistribution and use in source and binary forms, with or without
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  modification, are permitted provided that the following conditions are met:
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    * Redistributions of source code must retain the above copyright notice,
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  this list of conditions and the following disclaimer.
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    * Redistributions in binary form must reproduce the above copyright
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  notice, this list of conditions and the following disclaimer in the
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  documentation and/or other materials provided with the distribution.
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    * Neither the names of the copyright holders nor the names of their
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  contributors may be used to endorse or promote products derived from this
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  software without specific prior written permission.
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  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
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  PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER
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  OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
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  EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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  PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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  PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
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  LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
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  NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
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  SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#ifndef _LOG2F_H_
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#define _LOG2F_H_       1
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#include <spu_intrinsics.h>
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#include "headers/dom_chkf_less_than.h"
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/*
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 * FUNCTION
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 *      float _log2f(float x)
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 *
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 * DESCRIPTION
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 *      _log2f computes log (base 2) of the input value x. The log2f
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 *      function is approximated as a polynomial of order 8
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 *      (C. Hastings, Jr, 1955).
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 *
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 *                   __8__
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 *                   \
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 *                    \
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 *      log2f(1+x) =   /     Ci*x^i
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 *                   /____
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 *                    i=1
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 *
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 *      for x in the range 0.0 to 1.0
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 *
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 *      C1 =  1.4426898816672
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 *      C2 = -0.72116591947498
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 *      C3 =  0.47868480909345
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 *      C4 = -0.34730547155299
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 *      C5 =  0.24187369696082
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 *      C6 = -0.13753123777116
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 *      C7 =  0.052064690894143
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 *      C8 = -0.0093104962134977
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 *
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 *      This function assumes that x is a non-zero positive value.
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 */
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static __inline float _log2f(float x)
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{
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  union {
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    unsigned int ui;
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    float f;
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  } in;
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  int exponent;
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  float result;
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  float x2, x4;
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  float hi, lo;
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  vector float vx;
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  vector float vc = { 0.0, 0.0, 0.0, 0.0 };
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  in.f = x;
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  /* Extract the exponent from the input X.
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   */
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  exponent = (signed)((in.ui >> 23) & 0xFF) - 127;
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  /* Compute the remainder after removing the exponent.
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   */
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  in.ui -= exponent << 23;
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  /* Calculate the log2 of the remainder using the polynomial
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   * approximation.
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   */
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  x = in.f - 1.0f;
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  /* Instruction counts can be reduced if the polynomial was
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   * computed entirely from nested (dependent) fma's. However,
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   * to reduce the number of pipeline stalls, the polygon is evaluated
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   * in two halves (hi amd lo).
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   */
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  x2 = x * x;
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  x4 = x2 * x2;
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  hi = -0.0093104962134977f*x + 0.052064690894143f;
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  hi =                   hi*x - 0.13753123777116f;
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  hi =                   hi*x + 0.24187369696082f;
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  hi =                   hi*x - 0.34730547155299f;
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  lo =  0.47868480909345f  *x - 0.72116591947498f;
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  lo =                   lo*x + 1.4426898816672f;
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  lo =                   lo*x;
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  result = hi*x4 + lo;
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  /* Add the exponent back into the result.
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   */
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  result += (float)(exponent);
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#ifndef _IEEE_LIBM
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  vx = spu_promote(x, 0);
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  dom_chkf_less_than(vx, vc);
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#endif
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  return (result);
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}
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#endif /* _LOG2F_H_ */

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