mirror of
https://github.com/autc04/Retro68.git
synced 2024-12-04 16:50:57 +00:00
125 lines
3.8 KiB
C
125 lines
3.8 KiB
C
|
/*
|
||
|
(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_ */
|
||
|
|
||
|
|