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Adjust filter_fir to work with unsigned lengths

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This commit is contained in:
Kp 2022-11-12 19:31:52 +00:00
parent 527263d81e
commit 10d0bbc4e8
1 changed files with 11 additions and 4 deletions
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15
similar/arch/sdl/digi_mixer.cpp
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@ -37,6 +37,7 @@
#include "piggy.h"
#include "u_mem.h"
#include <memory>
#include "d_range.h"
#define MIX_DIGI_DEBUG 0
#define MIX_OUTPUT_FORMAT AUDIO_S16
@ -196,14 +197,20 @@ static std::unique_ptr<int16_t[]> filter_fir(int16_t *signal, int signalLen, con
for(int nn = 0; nn < signalLen; nn++)
{
// Determine start/stop indices for convolved chunk
int min_idx = std::max(0, nn - FILTER_LEN + 1);
int max_idx = std::min(nn, signalLen-1);
constexpr std::size_t coeffsLen = FILTER_LEN;
/* Avoid use of `std::max` here, since `nn + 1 < coeffsLen` would cause
* unsigned subtraction to underflow.
*/
const std::size_t min_idx = (nn + 1 > coeffsLen ? nn + 1 - coeffsLen : 0u);
const std::size_t max_idx = std::min(nn, signalLen - 1);
if (min_idx > max_idx)
continue;
int32_t cur_output = 0; // Increase bit size for fixed point expansion
// Sum over each sample * coefficient in this column
for(int kk = min_idx; kk <= max_idx; kk++)
for (const auto kk : xrange(min_idx, max_idx + 1))
{
int product = int32_t(signal[kk]) * coeffs[nn-kk];
const auto product = int32_t{signal[kk]} * coeffs[nn - kk];
cur_output = cur_output + product;
}