From a82b2da2dd19888ab0b3bc8534ff26b579f02b84 Mon Sep 17 00:00:00 2001
From: Andre Puschmann <andre@softwareradiosystems.com>
Date: Thu, 23 Apr 2020 10:19:53 +0200
Subject: [PATCH] dft_precoding: add helper to get largest valid PRB

---
 lib/include/srslte/phy/dft/dft_precoding.h | 2 ++
 lib/src/phy/dft/dft_precoding.c            | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/lib/include/srslte/phy/dft/dft_precoding.h b/lib/include/srslte/phy/dft/dft_precoding.h
index e87189e3f..2cbee27c8 100644
--- a/lib/include/srslte/phy/dft/dft_precoding.h
+++ b/lib/include/srslte/phy/dft/dft_precoding.h
@@ -53,6 +53,8 @@ SRSLTE_API void srslte_dft_precoding_free(srslte_dft_precoding_t* q);
 
 SRSLTE_API bool srslte_dft_precoding_valid_prb(uint32_t nof_prb);
 
+SRSLTE_API uint32_t srslte_dft_precoding_get_valid_prb(uint32_t nof_prb);
+
 SRSLTE_API int
 srslte_dft_precoding(srslte_dft_precoding_t* q, cf_t* input, cf_t* output, uint32_t nof_prb, uint32_t nof_symbols);
 
diff --git a/lib/src/phy/dft/dft_precoding.c b/lib/src/phy/dft/dft_precoding.c
index 3fdde3a7a..a68a4565f 100644
--- a/lib/src/phy/dft/dft_precoding.c
+++ b/lib/src/phy/dft/dft_precoding.c
@@ -102,6 +102,15 @@ bool srslte_dft_precoding_valid_prb(uint32_t nof_prb)
   return false;
 }
 
+/* Return largest integer that fulfills the DFT precoding PRB criterion (TS 36.213 Section 14.1.1.4C) */
+uint32_t srslte_dft_precoding_get_valid_prb(uint32_t nof_prb)
+{
+  while (srslte_dft_precoding_valid_prb(nof_prb) == false) {
+    nof_prb--;
+  }
+  return nof_prb;
+}
+
 int srslte_dft_precoding(srslte_dft_precoding_t* q, cf_t* input, cf_t* output, uint32_t nof_prb, uint32_t nof_symbols)
 {