LibAudio: Resample with integer ratios instead of floats

Floating-point ratios are inherently imprecise, and can lead to
unpredictable or nondeterministic behavior when resampling and expecting
a certain number of resulting samples. Therefore, the resampler now uses
integer ratios, with almost identical but fully predictable behavior.

This also introduces the reset() function that the FLAC loader will use
in the future.

1 files changed, 21 insertions, 8 deletions

diff --git a/Userland/Libraries/LibAudio/Buffer.cpp b/Userland/Libraries/LibAudio/Buffer.cpp
index efe6945a5f..1039f5bb3f 100644
--- a/Userland/Libraries/LibAudio/Buffer.cpp
+++ b/Userland/Libraries/LibAudio/Buffer.cpp
@@ -8,6 +8,7 @@
 #include "Buffer.h"
 #include <AK/Atomic.h>
 #include <AK/Debug.h>
+#include <AK/StdLibExtras.h>
 #include <AK/String.h>
 
 namespace Audio {
@@ -167,18 +168,19 @@ RefPtr<Buffer> Buffer::from_pcm_stream(InputMemoryStream& stream, ResampleHelper
 }
 
 template<typename SampleType>
-ResampleHelper<SampleType>::ResampleHelper(double source, double target)
-    : m_ratio(source / target)
+ResampleHelper<SampleType>::ResampleHelper(u32 source, u32 target)
+    : m_source(source)
+    , m_target(target)
 {
 }
-template ResampleHelper<i32>::ResampleHelper(double, double);
-template ResampleHelper<double>::ResampleHelper(double, double);
+template ResampleHelper<i32>::ResampleHelper(u32, u32);
+template ResampleHelper<double>::ResampleHelper(u32, u32);
 
 template<typename SampleType>
 Vector<SampleType> ResampleHelper<SampleType>::resample(Vector<SampleType> to_resample)
 {
     Vector<SampleType> resampled;
-    resampled.ensure_capacity(to_resample.size() * m_ratio);
+    resampled.ensure_capacity(to_resample.size() * ceil_div(m_source, m_target));
     for (auto sample : to_resample) {
         process_sample(sample, sample);
 
@@ -196,7 +198,7 @@ void ResampleHelper<SampleType>::process_sample(SampleType sample_l, SampleType
 {
     m_last_sample_l = sample_l;
     m_last_sample_r = sample_r;
-    m_current_ratio += 1;
+    m_current_ratio += m_target;
 }
 template void ResampleHelper<i32>::process_sample(i32, i32);
 template void ResampleHelper<double>::process_sample(double, double);
@@ -204,8 +206,8 @@ template void ResampleHelper<double>::process_sample(double, double);
 template<typename SampleType>
 bool ResampleHelper<SampleType>::read_sample(SampleType& next_l, SampleType& next_r)
 {
-    if (m_current_ratio > 0) {
-        m_current_ratio -= m_ratio;
+    if (m_current_ratio >= m_source) {
+        m_current_ratio -= m_source;
         next_l = m_last_sample_l;
         next_r = m_last_sample_r;
         return true;
@@ -216,4 +218,15 @@ bool ResampleHelper<SampleType>::read_sample(SampleType& next_l, SampleType& nex
 template bool ResampleHelper<i32>::read_sample(i32&, i32&);
 template bool ResampleHelper<double>::read_sample(double&, double&);
 
+template<typename SampleType>
+void ResampleHelper<SampleType>::reset()
+{
+    m_current_ratio = 0;
+    m_last_sample_l = {};
+    m_last_sample_r = {};
+}
+
+template void ResampleHelper<i32>::reset();
+template void ResampleHelper<double>::reset();
+
 }