From 566ac171f524992eba2e5ff695a0fc542745c9ac Mon Sep 17 00:00:00 2001
From: Max Kellermann <max@musicpd.org>
Date: Tue, 14 Jan 2020 18:02:51 +0100
Subject: [PATCH] pcm/Dsd2Pcm: generate `ctables` at compile time
---
src/pcm/Dsd2Pcm.cxx | 35 +++++++++++++++++++----------------
1 file changed, 19 insertions(+), 16 deletions(-)
diff --git a/src/pcm/Dsd2Pcm.cxx b/src/pcm/Dsd2Pcm.cxx
index 142bb5119..8b6818d37 100644
--- a/src/pcm/Dsd2Pcm.cxx
+++ b/src/pcm/Dsd2Pcm.cxx
@@ -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;