From 2c7195d80c4639e67f2f6d1115558402ae738b94 Mon Sep 17 00:00:00 2001
From: moneromooo-monero <moneromooo-monero@users.noreply.github.com>
Date: Fri, 9 Nov 2018 19:57:31 +0000
Subject: [PATCH] bulletproofs: avoid std::vector allocations for slice

---
 src/ringct/bulletproofs.cc | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/src/ringct/bulletproofs.cc b/src/ringct/bulletproofs.cc
index bed48769a..2b9976b62 100644
--- a/src/ringct/bulletproofs.cc
+++ b/src/ringct/bulletproofs.cc
@@ -31,6 +31,7 @@
 #include <stdlib.h>
 #include <boost/thread/mutex.hpp>
 #include "misc_log_ex.h"
+#include "span.h"
 #include "common/perf_timer.h"
 #include "cryptonote_config.h"
 extern "C"
@@ -217,7 +218,7 @@ static rct::key vector_power_sum(const rct::key &x, size_t n)
 }
 
 /* Given two scalar arrays, construct the inner product */
-static rct::key inner_product(const rct::keyV &a, const rct::keyV &b)
+static rct::key inner_product(const epee::span<const rct::key> &a, const epee::span<const rct::key> &b)
 {
   CHECK_AND_ASSERT_THROW_MES(a.size() == b.size(), "Incompatible sizes of a and b");
   rct::key res = rct::zero();
@@ -228,6 +229,11 @@ static rct::key inner_product(const rct::keyV &a, const rct::keyV &b)
   return res;
 }
 
+static rct::key inner_product(const rct::keyV &a, const rct::keyV &b)
+{
+  return inner_product(epee::span<const rct::key>(a.data(), a.size()), epee::span<const rct::key>(b.data(), b.size()));
+}
+
 /* Given two scalar arrays, construct the Hadamard product */
 static rct::keyV hadamard(const rct::keyV &a, const rct::keyV &b)
 {
@@ -293,7 +299,7 @@ static rct::keyV vector_subtract(const rct::keyV &a, const rct::key &b)
 }
 
 /* Multiply a scalar and a vector */
-static rct::keyV vector_scalar(const rct::keyV &a, const rct::key &x)
+static rct::keyV vector_scalar(const epee::span<const rct::key> &a, const rct::key &x)
 {
   rct::keyV res(a.size());
   for (size_t i = 0; i < a.size(); ++i)
@@ -303,6 +309,11 @@ static rct::keyV vector_scalar(const rct::keyV &a, const rct::key &x)
   return res;
 }
 
+static rct::keyV vector_scalar(const rct::keyV &a, const rct::key &x)
+{
+  return vector_scalar(epee::span<const rct::key>(a.data(), a.size()), x);
+}
+
 /* Create a vector from copies of a single value */
 static rct::keyV vector_dup(const rct::key &x, size_t N)
 {
@@ -400,17 +411,12 @@ static rct::keyV invert(rct::keyV x)
 }
 
 /* Compute the slice of a vector */
-static rct::keyV slice(const rct::keyV &a, size_t start, size_t stop)
+static epee::span<const rct::key> slice(const rct::keyV &a, size_t start, size_t stop)
 {
   CHECK_AND_ASSERT_THROW_MES(start < a.size(), "Invalid start index");
   CHECK_AND_ASSERT_THROW_MES(stop <= a.size(), "Invalid stop index");
   CHECK_AND_ASSERT_THROW_MES(start < stop, "Invalid start/stop indices");
-  rct::keyV res(stop - start);
-  for (size_t i = start; i < stop; ++i)
-  {
-    res[i - start] = a[i];
-  }
-  return res;
+  return epee::span<const rct::key>(&a[start], stop - start);
 }
 
 static rct::key hash_cache_mash(rct::key &hash_cache, const rct::key &mash0, const rct::key &mash1)