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From 6c9b134f7aceb70e4e3ec346f12e9f97553c1bd5 Mon Sep 17 00:00:00 2001
From: Ansgar Burchardt <Ansgar.Burchardt@tu-dresden.de>
Date: Wed, 20 Jun 2018 19:54:22 +0200
Subject: [PATCH] fix base64 encoder
The old implementation relied on undefined behavior (reading from a
union member not most recently written to), implementation-defined
layout and only worked on little endian.
This should make the `vtktest` test pass on big endian architectures.
---
dune/grid/io/file/vtk/b64enc.hh | 49 ++++++++++++++------------------
dune/grid/io/file/vtk/streams.hh | 12 ++++----
2 files changed, 28 insertions(+), 33 deletions(-)
diff --git a/dune/grid/io/file/vtk/b64enc.hh b/dune/grid/io/file/vtk/b64enc.hh
index 0f0aacbb1..f0fc4af27 100644
--- a/dune/grid/io/file/vtk/b64enc.hh
+++ b/dune/grid/io/file/vtk/b64enc.hh
@@ -27,53 +27,48 @@ namespace Dune {
'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
};
- /** @brief struct with three bytes of text */
- struct b64txt
+ /** @brief struct representing the three byte text as well as the four 6 bit chunks */
+ struct b64chunk
{
- typedef unsigned char size_type;
+ using size_type = unsigned char;
size_type size;
char txt[3];
+
+ void reset()
+ {
+ size = 0;
+ txt[0] = txt[1] = txt[2] = 0;
+ }
+
int read(const char* t, size_type s)
{
size = s>=3 ? 3 : s;
- txt[2] = s>0 ? t[0] : 0;
+ txt[0] = s>0 ? t[0] : 0;
txt[1] = s>1 ? t[1] : 0;
- txt[0] = s>2 ? t[2] : 0;
+ txt[2] = s>2 ? t[2] : 0;
return size;
}
+
void put(const char c)
{
assert (size < 3);
- txt[2-size++] = c;
+ txt[size++] = c;
}
- };
- /** struct with four six bit chunks */
- struct b64data
- {
- typedef unsigned char size_type;
- size_type size;
- unsigned A : 6;
- unsigned B : 6;
- unsigned C : 6;
- unsigned D : 6;
void write(char* t)
{
- t[3] = size>2 ? base64table[A] : '=';
- t[2] = size>1 ? base64table[B] : '=';
- t[1] = size>0 ? base64table[C] : '=';
- t[0] = size>0 ? base64table[D] : '=';
+ const unsigned A = (txt[0] & 0b1111'1100) >> 2;
+ const unsigned B = (txt[0] & 0b0000'0011) << 4 | (txt[1] & 0b1111'0000) >> 4;
+ const unsigned C = (txt[1] & 0b0000'1111) << 2 | (txt[2] & 0b1100'0000) >> 6;
+ const unsigned D = txt[2] & 0b0011'1111;
+ t[0] = size>0 ? base64table[A] : '=';
+ t[1] = size>0 ? base64table[B] : '=';
+ t[2] = size>1 ? base64table[C] : '=';
+ t[3] = size>2 ? base64table[D] : '=';
size = 0;
}
};
- /** @brief union representing the three byte text as well as the four 6 bit chunks */
- union b64chunk
- {
- b64txt txt;
- b64data data;
- };
-
/** @} */
} // namespace Dune
diff --git a/dune/grid/io/file/vtk/streams.hh b/dune/grid/io/file/vtk/streams.hh
index b6f84c7a2..2df7c26e1 100644
--- a/dune/grid/io/file/vtk/streams.hh
+++ b/dune/grid/io/file/vtk/streams.hh
@@ -26,7 +26,7 @@ namespace Dune {
: s(s_)
{
// reset chunk
- chunk.txt.read(0,0);
+ chunk.reset();
}
//! encode a data item
@@ -42,10 +42,10 @@ namespace Dune {
char* p = reinterpret_cast<char*>(&data);
for (size_t len = sizeof(X); len > 0; len--,p++)
{
- chunk.txt.put(*p);
- if (chunk.txt.size == 3)
+ chunk.put(*p);
+ if (chunk.size == 3)
{
- chunk.data.write(obuf);
+ chunk.write(obuf);
s.write(obuf,4);
}
}
@@ -61,9 +61,9 @@ namespace Dune {
*/
void flush()
{
- if (chunk.txt.size > 0)
+ if (chunk.size > 0)
{
- chunk.data.write(obuf);
+ chunk.write(obuf);
s.write(obuf,4);
}
}
--
2.17.1
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