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[PATCH] Exploit move semantics in std::accumulate.
- From: Eelis van der Weegen <eelis at eelis dot net>
- To: libstdc++ at gcc dot gnu dot org
- Date: Sat, 08 Jan 2011 18:27:51 +0100
- Subject: [PATCH] Exploit move semantics in std::accumulate.
The attached simple patch reduces the runtime of the following program
from 1.4 seconds to 0.005 seconds on my machine:
#include <iostream>
#include <string>
#include <numeric>
#include <vector>
int main()
{
std::vector<std::string> v;
for(int i = 0; i != 20000; ++i)
v.push_back(std::string(50, 'a'+(i%10)));
std::cout << std::accumulate(v.begin(), v.end(),
std::string()).size() << '\n';
}
Regards,
Eelis
>From 3176b9c351aa87b2b5e786a303acb59d99eaec58 Mon Sep 17 00:00:00 2001
From: Eelis van der Weegen <eelis@eelis.net>
Date: Sat, 8 Jan 2011 18:20:05 +0100
Subject: [PATCH] Exploit move semantics in std::accumulate.
---
libstdc++-v3/include/bits/stl_numeric.h | 4 ++--
1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/bits/stl_numeric.h b/libstdc++-v3/include/bits/stl_numeric.h
index 86ae2cf..61b7d06 100644
--- a/libstdc++-v3/include/bits/stl_numeric.h
+++ b/libstdc++-v3/include/bits/stl_numeric.h
@@ -120,7 +120,7 @@ _GLIBCXX_BEGIN_NESTED_NAMESPACE(std, _GLIBCXX_STD_P)
__glibcxx_requires_valid_range(__first, __last);
for (; __first != __last; ++__first)
- __init = __init + *__first;
+ __init = _GLIBCXX_MOVE(__init) + *__first;
return __init;
}
@@ -147,7 +147,7 @@ _GLIBCXX_BEGIN_NESTED_NAMESPACE(std, _GLIBCXX_STD_P)
__glibcxx_requires_valid_range(__first, __last);
for (; __first != __last; ++__first)
- __init = __binary_op(__init, *__first);
+ __init = __binary_op(_GLIBCXX_MOVE(__init), *__first);
return __init;
}
--
1.7.1