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pcm/Dsd2Pcm: generate ctables at compile time

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This commit is contained in:
Max Kellermann 2020-01-14 18:02:51 +01:00
parent 8aaf39efd6
commit 566ac171f5
1 changed files with 19 additions and 16 deletions
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35
src/pcm/Dsd2Pcm.cxx
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@ -32,6 +32,7 @@ or implied, of Sebastian Gesemann.
#include "Dsd2Pcm.hxx"
#include "util/bit_reverse.h"
#include "util/GenerateArray.hxx"
#include <stdlib.h>
#include <string.h>
@ -121,9 +122,6 @@ static constexpr double htaps[HTAPS] = {
3.130441005359396e-08
};
static float ctables[CTABLES][256];
static int precalculated = 0;
static constexpr float
CalculateCtableValue(int t, int k, int e) noexcept
{
@ -135,21 +133,27 @@ CalculateCtableValue(int t, int k, int e) noexcept
return acc;
}
static void
precalc() noexcept
{
int t, e, k;
if (precalculated) return;
for (t=0; t<CTABLES; ++t) {
k = HTAPS - t*8;
if (k>8) k=8;
for (e=0; e<256; ++e) {
ctables[CTABLES-1-t][e] = CalculateCtableValue(t, k, e);
}
/* this needs to be a struct because GCC 6 doesn't have constexpr
lambdas (C++17) */
struct GenerateCtableValue {
int t, k;
constexpr auto operator()(int e) const noexcept {
return CalculateCtableValue(t, k, e);
}
precalculated = 1;
};
static constexpr auto
GenerateCtable(int t) noexcept
{
int k = HTAPS - t*8;
if (k>8) k=8;
return GenerateArray<256>(GenerateCtableValue{CTABLES - 1 - t, k});
}
static constexpr auto ctables = GenerateArray<CTABLES>(GenerateCtable);
struct dsd2pcm_ctx_s
{
unsigned char fifo[FIFOSIZE];
@ -160,7 +164,6 @@ dsd2pcm_ctx *
dsd2pcm_init() noexcept
{
dsd2pcm_ctx* ptr;
if (!precalculated) precalc();
ptr = (dsd2pcm_ctx*) malloc(sizeof(dsd2pcm_ctx));
if (ptr) dsd2pcm_reset(ptr);
return ptr;