From c5f103b43e46b3b0ca7d28f18e5766b2da23f8eb Mon Sep 17 00:00:00 2001
From: Sarod Yatawatta <yatawatta@astron.nl>
Date: Mon, 14 Dec 2020 16:38:48 +0000
Subject: [PATCH] COB-153: simplify phi calculation

---
 RTCP/Cobalt/GPUProc/share/gpu/kernels/FIR_Filter.cu | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/RTCP/Cobalt/GPUProc/share/gpu/kernels/FIR_Filter.cu b/RTCP/Cobalt/GPUProc/share/gpu/kernels/FIR_Filter.cu
index 2ce0e70c538..5d49d4e4ba5 100644
--- a/RTCP/Cobalt/GPUProc/share/gpu/kernels/FIR_Filter.cu
+++ b/RTCP/Cobalt/GPUProc/share/gpu/kernels/FIR_Filter.cu
@@ -207,18 +207,17 @@ __global__ void FIR_filter( void *filteredDataPtr,
   // We only need the term that changes with t, so discard the rest
   // and only keep : 2 pi f (tau_1 - tau_0) (t/T) for the rest of calculations
   // also replace f with f/f_s where f_s is sample frequency = clock/1024
-  const double phiGradient = 2.0 * M_PI * (subbandFrequency / (CLOCK_MHZ*1e6/1024.0) )*( delayAfterEnd - delayAtBegin )/NR_SAMPLES_PER_CHANNEL;
-
+  // phi = phiGradient x blockOffset
   // Offset of this sample between begin and end. = t/T fraction, within one FFT block of NR_CHANNELS
-  const double blockOffset = double(channel) / NR_CHANNELS;
-  // Interpolate the required phase rotation for this sample.
+  const double phi = 2.0 * M_PI * (subbandFrequency / (CLOCK_MHZ*1e6/1024.0) )*( delayAfterEnd - delayAtBegin )/NR_SAMPLES_PER_CHANNEL * double(channel)/NR_CHANNELS;
+
   //
   // Use double precision here, when phi~=0, error in cos() is minimum
   // but error in sin() is highest, and will affect most baselines (whose Doppler effect ~=0)
   // Note: both X and Y polarizations will have same correction
   // so real=cos(phi), imag=sin(phi) correction factor
   // phi=phiGradient * blockOffset
-  const float FACTOR=sincos_d2f_select(phiGradient  * blockOffset, ri);
+  const float FACTOR=sincos_d2f_select(phi, ri);
 #endif
 
   //# const float16 weights = (*weightsData)[channel];
-- 
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