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Implement p_exp aproximation function #147

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Implement p_exp aproximation function #147

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fae6e34
math: p_exp: Implement exponential function
Vermillionaire Jun 15, 2015
a98f111
Removed leftover includes
Vermillionaire Jun 15, 2015
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17 changes: 13 additions & 4 deletions src/math/p_exp.c
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Original file line number Diff line number Diff line change
@@ -1,10 +1,12 @@
#include <pal.h>

/**
*
* Calculate exponent (e^a), where e is the base of the natural logarithm
* (2.71828.)
*
* Based of the algorithm in this paper: http://www.schraudolph.org/pubs/Schraudolph99.pdf,
* It calculates a approximation of e^a very efficiently, but at the cost of accuracy.
*
* @param a Pointer to input vector
*
* @param c Pointer to output vector
Expand All @@ -14,12 +16,19 @@
* @return None
*
*/
#include <math.h>

void p_exp_f32(const float *a, float *c, int n)
{

int i;
for (i = 0; i < n; i++) {
*(c + i) = expf(*(a + i));
union
{
float f;
uint32_t i;
} u;

// = 2^23 / M_LN2 * (*(a+i)) + (127 * 2^23 - 100000)
u.i = 12102203.16156 * ( *( a + i )) + (1065353216 - 100000);
*(c + i) = u.f;
}
}