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Diffstat (limited to 'newlib/libm/machine/spu/headers/log2f.h')
| -rw-r--r-- | newlib/libm/machine/spu/headers/log2f.h | 115 |
1 files changed, 115 insertions, 0 deletions
diff --git a/newlib/libm/machine/spu/headers/log2f.h b/newlib/libm/machine/spu/headers/log2f.h new file mode 100644 index 000000000..b72665fd4 --- /dev/null +++ b/newlib/libm/machine/spu/headers/log2f.h @@ -0,0 +1,115 @@ +/* + (C) Copyright 2001,2006, + International Business Machines Corporation, + Sony Computer Entertainment, Incorporated, + Toshiba Corporation, + + All rights reserved. + + Redistribution and use in source and binary forms, with or without + modification, are permitted provided that the following conditions are met: + + * Redistributions of source code must retain the above copyright notice, + this list of conditions and the following disclaimer. + * Redistributions in binary form must reproduce the above copyright + notice, this list of conditions and the following disclaimer in the + documentation and/or other materials provided with the distribution. + * Neither the names of the copyright holders nor the names of their + contributors may be used to endorse or promote products derived from this + software without specific prior written permission. + + THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS + IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED + TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A + PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER + OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, + EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, + PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR + PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF + LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING + NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS + SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. +*/ +#ifndef _LOG2F_H_ +#define _LOG2F_H_ 1 + +/* + * FUNCTION + * float _log2f(float x) + * + * DESCRIPTION + * _log2f computes log (base 2) of the input value x. The log2f + * function is approximated as a polynomial of order 8 + * (C. Hastings, Jr, 1955). + * + * __8__ + * \ + * \ + * log2f(1+x) = / Ci*x^i + * /____ + * i=1 + * + * for x in the range 0.0 to 1.0 + * + * C1 = 1.4426898816672 + * C2 = -0.72116591947498 + * C3 = 0.47868480909345 + * C4 = -0.34730547155299 + * C5 = 0.24187369696082 + * C6 = -0.13753123777116 + * C7 = 0.052064690894143 + * C8 = -0.0093104962134977 + * + * This function assumes that x is a non-zero positive value. + */ + +static __inline float _log2f(float x) +{ + union { + unsigned int ui; + float f; + } in; + int exponent; + float result; + float x2, x4; + float hi, lo; + + in.f = x; + + /* Extract the exponent from the input X. + */ + exponent = (signed)((in.ui >> 23) & 0xFF) - 127; + + /* Compute the remainder after removing the exponent. + */ + in.ui -= exponent << 23; + + /* Calculate the log2 of the remainder using the polynomial + * approximation. + */ + x = in.f - 1.0f; + + /* 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). + */ + x2 = x * x; + x4 = x2 * x2; + hi = -0.0093104962134977f*x + 0.052064690894143f; + hi = hi*x - 0.13753123777116f; + hi = hi*x + 0.24187369696082f; + hi = hi*x - 0.34730547155299f; + lo = 0.47868480909345f *x - 0.72116591947498f; + lo = lo*x + 1.4426898816672f; + lo = lo*x; + result = hi*x4 + lo; + + /* Add the exponent back into the result. + */ + result += (float)(exponent); + + return (result); +} + +#endif /* _LOG2F_H_ */ |