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Diffstat (limited to 'newlib/libm/machine/spu/headers/exp2f.h')
| -rw-r--r-- | newlib/libm/machine/spu/headers/exp2f.h | 124 |
1 files changed, 124 insertions, 0 deletions
diff --git a/newlib/libm/machine/spu/headers/exp2f.h b/newlib/libm/machine/spu/headers/exp2f.h new file mode 100644 index 000000000..84bccdc04 --- /dev/null +++ b/newlib/libm/machine/spu/headers/exp2f.h @@ -0,0 +1,124 @@ +/* + (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 _EXP2F_H_ +#define _EXP2F_H_ 1 + +#ifndef M_LN2 +#define M_LN2 0.69314718055994530942 /* ln(2) */ +#endif /* M_LN2 */ + +/* + * FUNCTION + * float _exp2f(float x) + * + * DESCRIPTION + * _exp2f computes 2 raised to the input 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=0 + * + * 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 float _exp2f(float x) +{ + union { + float f; + unsigned int ui; + } bias, exp_int, exp_frac; + unsigned int overflow, underflow; + int ix; + float frac, frac2, frac4; + float hi, lo; + + /* Break in the input x into two parts ceil(x), x - ceil(x). + */ + bias.f = x; + bias.ui = ~(unsigned int)((signed)(bias.ui) >> 31) & 0x3F7FFFFF; + ix = (int)(x + bias.f); + frac = (float)ix - x; + frac *= (float)(M_LN2); + + exp_int.ui = (ix + 127) << 23; + + overflow = (ix > 128) ? 0x7FFFFFFF : 0x0; + underflow = (ix < -127) ? 0xFFFFFFFF : 0x0; + + /* 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 = frac * frac; + frac4 = frac2 * frac2; + hi = -0.0001413161f * frac + 0.0013298820f; + hi = hi * frac - 0.0083013598f; + hi = hi * frac + 0.0416573475f; + lo = -0.1666653019f * frac + 0.4999999206f; + lo = lo * frac - 0.9999999995f; + lo = lo * frac + 1.0f; + exp_frac.f = hi * frac4 + lo; + + ix += exp_frac.ui >> 23; + exp_frac.f *= exp_int.f; + + exp_frac.ui = (exp_frac.ui | overflow) & ~underflow; + + return (exp_frac.f); +} + +#endif /* _EXP2F_H_ */ + + |