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A faster implementation (only basic functions so far)

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Joshua Moerman 2013-12-01 17:39:18 +01:00
parent 0fcfd492f8
commit 2466cd2a7c
1 changed files with 62 additions and 0 deletions
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wavelet/wavelet2.hpp
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#pragma once
#include "wavelet_constants.hpp"
/* Rewrite of the basic functions
* This will make the adaption for the parallel case easier,
* because we can explicitly pass the two elements which are out of range
* (these are normally wrap-around values)
*
* These are also faster (testcase: size = 8, stride = 1, iterations = 100000)
* V2 0.00377901
* V1 0.0345114
*
* But also less abstract (which can be both a good thing and bad thing)
*
*/
namespace wvlt{
inline namespace V2 {
double inner_product(double* x, double const* coef, unsigned int stride){
return x[0] * coef[0] + x[stride] * coef[1] + x[2*stride] * coef[2] + x[3*stride] * coef[3];
}
// will overwrite x, x1 and x2 are next elements, or wrap around
// size is size of vector x (so x[size-1] is valid)
void wavelet_mul(double* x, double x1, double x2, unsigned int size, unsigned int stride){
assert(is_pow_of_two(size) && is_pow_of_two(stride) && 4*stride <= size);
for(int i = 0; i < size - 2*stride; i += 2*stride){
double y1 = inner_product(x + i, evn_coef, stride);
double y2 = inner_product(x + i, odd_coef, stride);
x[i] = y1;
x[i+stride] = y2;
}
int i = size - 2*stride;
double y1 = x[i] * evn_coef[0] + x[i+stride] * evn_coef[1] + x1 * evn_coef[2] + x2 * evn_coef[3];
double y2 = x[i] * odd_coef[0] + x[i+stride] * odd_coef[1] + x1 * odd_coef[2] + x2 * odd_coef[3];
x[i] = y1;
x[i+stride] = y2;
}
// will overwrite x, x2 and x1 are previous elements, or wrap around
// size is size of vector x (so x[size-1] is valid)
void wavelet_inv(double* x, double x1, double x2, unsigned int size, unsigned int stride){
assert(is_pow_of_two(size) && is_pow_of_two(stride) && 4*stride <= size);
for(int i = size - 2*stride; i >= 2*stride; i -= 2*stride){
double y1 = inner_product(x + i - 2*stride, evn_coef_inv, stride);
double y2 = inner_product(x + i - 2*stride, odd_coef_inv, stride);
x[i] = y1;
x[i+stride] = y2;
}
int i = 0;
double y1 = x2 * evn_coef_inv[0] + x1 * evn_coef_inv[1] + x[i] * evn_coef_inv[2] + x[i+stride] * evn_coef_inv[3];
double y2 = x2 * odd_coef_inv[0] + x1 * odd_coef_inv[1] + x[i] * odd_coef_inv[2] + x[i+stride] * odd_coef_inv[3];
x[i] = y1;
x[i+stride] = y2;
}
}
}