Hi,
I have made an extension for the reverse function in std_vector.hh. The
code suggests to implement template specialisation for reverse vector<int>.
This is what I have done, plus specialisation for float and double vectors.
The code depends on the availability of memrev, which is not available
on all platforms.So a check is required (during configure) to
(con)figure out if memrev is supported,. The result of the check being
that the symbol MEMREV_SUPPORTED must be defined. I don't know how to
implement this.
In case memrev is not available there are two options:
1. skip the specialized template implementation for <int> <float>
<double> and keep the generic template code. This is what is implemented
now.
2. implement a replacement for memrev. a simple replacement is added
below. I don't know where to put it.
it uses malloc to allocate memory for each item. This can also be done
using alloca, which allocates memory on the stack and, as a consequence,
does not have to be freed. but for alloca the same holds as for memrev,
it is not supported on all platforms so additional complexity has to be
added t to the configure scripting to determine whether alloca is
supported, so I left that out.
Bye,
Ruud van Silfhout
additional memrev implementation:
void *memrev(void *block, size_t elsize, size_t elnum)
{
void *pSwap = malloc(elsize); // could have nbeen alloca(elsize)
char *pLeft = (char*)block;
char *pRight = (char*)block + (elnum-1)*elsize;
while (pLeft < pRight)
{
memcpy (pSwap, pLeft, elsize);
memcpy (pLeft, pRight, elsize);
memcpy (pRight, pSwap, elsize);
pLeft += elsize;
pRight -= elsize;
}
free(pSwap); // not needed if alloca is used
return block;
}
Index: flower/include/std-vector.hh
===================================================================
RCS file: /sources/lilypond/lilypond/flower/include/std-vector.hh,v
retrieving revision 1.26
diff -u -r1.26 std-vector.hh
--- flower/include/std-vector.hh 7 Sep 2006 11:16:10 -0000 1.26
+++ flower/include/std-vector.hh 7 Sep 2006 19:52:35 -0000
@@ -222,13 +222,32 @@
}
#endif
+#ifdef MEMREV_SUPPORTED
+void
+reverse (vector<int> &v)
+{
+ memrev (v.begin (), sizeof(int), v.size ());
+}
+
+void
+reverse (vector<float> &v)
+{
+ memrev (v.begin (), sizeof(float), v.size ());
+}
+
+void
+reverse (vector<double> &v)
+{
+ memrev (v.begin (), sizeof(double), v.size ());
+}
+
+#endif
+
template<typename T>
void
reverse (vector<T> &v)
{
- // CHECKME: for a simple vector, like vector<int>, this should
- // expand to memrev.
- reverse (v.begin (), v.end ());
+ reverse (v.begin(), v.end ());
}
template<typename T>
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