From 1481d89dfd47099ec7a14693b6f6fddafd00d5e9 Mon Sep 17 00:00:00 2001
From: Bartosz Podrygajlo <bartosz.podrygajlo@openairinterface.org>
Date: Mon, 9 Dec 2024 12:56:56 +0100
Subject: [PATCH] Optimize PHY_ofdm_mod CYCLIC_PREFIX in case of incidentally
 aligned pointers

It seems that the cyclic prefix is in most cases a multiple of 512 samples.
This means that in most cases the idft output pointer is already aligned and
there is no need to perform an extra memcpy. This saves the memcpy time in
most cyclic prefix insertion cases.
---
 openair1/PHY/MODULATION/ofdm_mod.c | 57 +++++++++++++++---------------
 1 file changed, 28 insertions(+), 29 deletions(-)

diff --git a/openair1/PHY/MODULATION/ofdm_mod.c b/openair1/PHY/MODULATION/ofdm_mod.c
index 4d0abf7b61..61487eb433 100644
--- a/openair1/PHY/MODULATION/ofdm_mod.c
+++ b/openair1/PHY/MODULATION/ofdm_mod.c
@@ -133,12 +133,6 @@ void PHY_ofdm_mod(int *input, /// pointer to complex input
   if (nb_symbols == 0)
     return;
 
-  int16_t temp[2 * 2 * 6144 * 4] __attribute__((aligned(32)));
-  int i, j;
-
-  volatile int *output_ptr = (int *)0;
-
-  int *temp_ptr = (int *)0;
   idft_size_idx_t idft_size = get_idft(fftsize);
 
 #ifdef DEBUG_OFDM_MOD
@@ -150,7 +144,7 @@ void PHY_ofdm_mod(int *input, /// pointer to complex input
          output);
 #endif
 
-  for (i = 0; i < nb_symbols; i++) {
+  for (int i = 0; i < nb_symbols; i++) {
 #ifdef DEBUG_OFDM_MOD
     printf("[PHY] symbol %d/%d offset %d (%p,%p -> %p)\n",
            i,
@@ -162,57 +156,62 @@ void PHY_ofdm_mod(int *input, /// pointer to complex input
 #endif
 
     // on AVX2 need 256-bit alignment
-    idft(idft_size, (int16_t *)&input[i * fftsize], (int16_t *)temp, 1);
 
     // Copy to frame buffer with Cyclic Extension
     // Note:  will have to adjust for synchronization offset!
 
     switch (etype) {
-      case CYCLIC_PREFIX:
-        output_ptr = &output[(i * fftsize) + ((1 + i) * nb_prefix_samples)];
-        temp_ptr = (int *)temp;
-
-        //      msg("Doing cyclic prefix method\n");
-
-        {
-          memcpy((void *)output_ptr, (void *)temp_ptr, fftsize << 2);
+      case CYCLIC_PREFIX: {
+        int *output_ptr = &output[(i * fftsize) + ((1 + i) * nb_prefix_samples)];
+        if ((uintptr_t)output_ptr % 32 == 0) {
+          // output ptr is aligned, do ifft inplace
+          idft(idft_size, (int16_t *)&input[i * fftsize], (int16_t *)output_ptr, 1);
+        } else {
+          // output ptr is not aligned, needs an extra memcpy
+          c16_t temp[fftsize] __attribute__((aligned(32)));
+          idft(idft_size, (int16_t *)&input[i * fftsize], (int16_t *)temp, 1);
+          memcpy((void *)output_ptr, (void *)temp, fftsize << 2);
         }
+        // perform cyclic prefix insertion
         memcpy((void *)&output_ptr[-nb_prefix_samples], (void *)&output_ptr[fftsize - nb_prefix_samples], nb_prefix_samples << 2);
         break;
+      }
 
-      case CYCLIC_SUFFIX:
+      case CYCLIC_SUFFIX: {
+        c16_t temp[fftsize] __attribute__((aligned(32)));
+        idft(idft_size, (int16_t *)&input[i * fftsize], (int16_t *)temp, 1);
+        int *output_ptr = &output[(i * fftsize) + (i * nb_prefix_samples)];
 
-        output_ptr = &output[(i * fftsize) + (i * nb_prefix_samples)];
-
-        temp_ptr = (int *)temp;
+        int *temp_ptr = (int *)temp;
 
         //      msg("Doing cyclic suffix method\n");
 
-        for (j = 0; j < fftsize; j++) {
+        for (int j = 0; j < fftsize; j++) {
           output_ptr[j] = temp_ptr[2 * j];
         }
 
-        for (j = 0; j < nb_prefix_samples; j++)
+        for (int j = 0; j < nb_prefix_samples; j++)
           output_ptr[fftsize + j] = output_ptr[j];
-
         break;
+      }
 
       case ZEROS:
 
         break;
 
-      case NONE:
-
+      case NONE: {
+        c16_t temp[fftsize] __attribute__((aligned(32)));
+        idft(idft_size, (int16_t *)&input[i * fftsize], (int16_t *)temp, 1);
         //      msg("NO EXTENSION!\n");
-        output_ptr = &output[fftsize];
+        int *output_ptr = &output[fftsize];
 
-        temp_ptr = (int *)temp;
+        int *temp_ptr = (int *)temp;
 
-        for (j = 0; j < fftsize; j++) {
+        for (int j = 0; j < fftsize; j++) {
           output_ptr[j] = temp_ptr[2 * j];
         }
-
         break;
+      }
 
       default:
         break;