ref: 67ee8b982972c8d5a63416a5edbdbbc367f2d162
parent: 9f002b618081265a0051110502710d414776e4c2
author: Clownacy <Clownacy@users.noreply.github.com>
date: Thu Sep 3 10:28:04 EDT 2020
Optimise the Lanczos resampler some more
--- a/src/Backends/Audio/SoftwareMixer.cpp
+++ b/src/Backends/Audio/SoftwareMixer.cpp
@@ -10,6 +10,8 @@
#define MAX(a, b) ((a) > (b) ? (a) : (b))
#define CLAMP(x, y, z) MIN(MAX((x), (y)), (z))
+#define LANCZOS_KERNEL_RADIUS 2
+
struct Mixer_Sound
{signed char *samples;
@@ -51,10 +53,11 @@
if (sound == NULL)
return NULL;
+ // Both interpolators will read outside the array's bounds, so allocate some extra room
#ifdef LANCZOS_RESAMPLER
- sound->samples = (signed char*)malloc(length);
+ sound->samples = (signed char*)malloc(LANCZOS_KERNEL_RADIUS - 1 + length + LANCZOS_KERNEL_RADIUS);
#else
- sound->samples = (signed char*)malloc(length + 1); // +1 for the linear-interpolator
+ sound->samples = (signed char*)malloc(length + 1);
#endif
if (sound->samples == NULL)
@@ -63,6 +66,14 @@
return NULL;
}
+#ifdef LANCZOS_RESAMPLER
+ // Blank samples outside the array bounds (we'll deal with the other half later)
+ for (size_t i = 0; i < LANCZOS_KERNEL_RADIUS - 1; ++i)
+ sound->samples[i] = 0;
+
+ sound->samples += LANCZOS_KERNEL_RADIUS - 1;
+#endif
+
for (size_t i = 0; i < length; ++i)
sound->samples[i] = samples[i] - 0x80; // Convert from unsigned 8-bit PCM to signed
@@ -88,6 +99,9 @@
if (*sound_pointer == sound)
{*sound_pointer = sound->next;
+ #ifdef LANCZOS_RESAMPLER
+ sound->samples -= LANCZOS_KERNEL_RADIUS - 1;
+ #endif
free(sound->samples);
free(sound);
break;
@@ -100,8 +114,17 @@
sound->playing = true;
sound->looping = looping;
-#ifndef LANCZOS_RESAMPLER
- sound->samples[sound->frames] = looping ? sound->samples[0] : 0; // For the linear interpolator
+ // Fill the out-of-bounds part of the buffer with
+ // either blank samples or repeated samples
+#ifdef LANCZOS_RESAMPLER
+ if (looping)
+ for (size_t i = 0; i < LANCZOS_KERNEL_RADIUS; ++i)
+ sound->samples[sound->frames + i] = sound->samples[i];
+ else
+ for (size_t i = 0; i < LANCZOS_KERNEL_RADIUS; ++i)
+ sound->samples[sound->frames + i] = 0;
+#else
+ sound->samples[sound->frames] = looping ? sound->samples[0] : 0;
#endif
}
@@ -151,13 +174,11 @@
{#ifdef LANCZOS_RESAMPLER
// Perform Lanczos resampling
- const int kernel_radius = 2;
-
float accumulator = 0;
- for (int i = -MIN(kernel_radius - 1, sound->position); i <= kernel_radius; ++i)
+ for (int i = -LANCZOS_KERNEL_RADIUS + 1; i <= LANCZOS_KERNEL_RADIUS; ++i)
{- const signed char input_sample = sound->samples[(sound->position + i) % sound->frames];
+ const signed char input_sample = sound->samples[sound->position + i];
const float kernel_input = ((float)sound->position_subsample / 0x10000) - i;
@@ -168,7 +189,7 @@
else
{const float nx = 3.14159265358979323846f * kernel_input;
- const float nxa = nx / kernel_radius;
+ const float nxa = nx / LANCZOS_KERNEL_RADIUS;
accumulator += input_sample * (sin(nx) * sin(nxa) / (nx * nxa));
}