Add a method to process two biquads at once

2 files changed, 50 insertions, 1 deletions

diff --git a/alc/filters/biquad.cpp b/alc/filters/biquad.cpp
index 271ca696..fefdc8e1 100644
--- a/alc/filters/biquad.cpp
+++ b/alc/filters/biquad.cpp
@@ -120,5 +120,44 @@ void BiquadFilterR<Real>::process(const al::span<const Real> src, Real *dst)
     mZ2 = z2;
 }
 
+template<typename Real>
+void BiquadFilterR<Real>::dualProcess(BiquadFilterR &other, const al::span<const Real> src,
+    Real *dst)
+{
+    const Real b00{mB0};
+    const Real b01{mB1};
+    const Real b02{mB2};
+    const Real a01{mA1};
+    const Real a02{mA2};
+    const Real b10{other.mB0};
+    const Real b11{other.mB1};
+    const Real b12{other.mB2};
+    const Real a11{other.mA1};
+    const Real a12{other.mA2};
+    Real z01{mZ1};
+    Real z02{mZ2};
+    Real z11{other.mZ1};
+    Real z12{other.mZ2};
+
+    auto proc_sample = [b00,b01,b02,a01,a02,b10,b11,b12,a11,a12,&z01,&z02,&z11,&z12](Real input) noexcept -> Real
+    {
+        const Real tmpout{input*b00 + z01};
+        z01 = input*b01 - tmpout*a01 + z02;
+        z02 = input*b02 - tmpout*a02;
+        input = tmpout;
+
+        const Real output{input*b10 + z11};
+        z11 = input*b11 - output*a11 + z12;
+        z12 = input*b12 - output*a12;
+        return output;
+    };
+    std::transform(src.cbegin(), src.cend(), dst, proc_sample);
+
+    mZ1 = z01;
+    mZ2 = z02;
+    other.mZ1 = z11;
+    other.mZ2 = z12;
+}
+
 template class BiquadFilterR<float>;
 template class BiquadFilterR<double>;
diff --git a/alc/filters/biquad.h b/alc/filters/biquad.h
index 30eed57d..3ce70cb3 100644
--- a/alc/filters/biquad.h
+++ b/alc/filters/biquad.h
@@ -114,8 +114,9 @@ public:
         mA2 = other.mA2;
     }
 
-
     void process(const al::span<const Real> src, Real *dst);
+    /** Processes this filter and the other at the same time. */
+    void dualProcess(BiquadFilterR &other, const al::span<const Real> src, Real *dst);
 
     /* Rather hacky. It's just here to support "manual" processing. */
     std::pair<Real,Real> getComponents() const noexcept { return {mZ1, mZ2}; }
@@ -129,6 +130,15 @@ public:
     }
 };
 
+template<typename Real>
+struct DualBiquadR {
+    BiquadFilterR<Real> &f0, &f1;
+
+    void process(const al::span<const Real> src, Real *dst)
+    { f0.dualProcess(f1, src, dst); }
+};
+
 using BiquadFilter = BiquadFilterR<float>;
+using DualBiquad = DualBiquadR<float>;
 
 #endif /* FILTERS_BIQUAD_H */