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Fix reading of book file

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Bug is subtle because appears only under MSVC 32 bits in
optimized version, hence was missed before.

Bug is due to the fact that evaluation order of terms of a
sum is undefined by the standard, so in get_int() we have:

return 256 * get_int<n-1>() + bookFile.get();

And if get() is evaluated before get_int() we have a corrupted
key.

The patch rewrites the code in a more natural and predictable way.

No functional change.

Signed-off-by: Marco Costalba <mcostalba@gmail.com>
This commit is contained in:
Marco Costalba 2011-05-07 09:03:59 +01:00
parent 339bf9b7e1
commit 2535dc1340
2 changed files with 17 additions and 11 deletions
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17
src/book.cpp
View file

@ -502,6 +502,18 @@ int Book::find_entry(uint64_t key) {
}
/// Book::get_number() reads sizeof(T) chars from the file's binary byte
/// stream and converts them in a number of type T.
template<typename T>
void Book::get_number(T& n) {
n = 0;
for (size_t i = 0; i < sizeof(T); i++)
n = (n << 8) + (T)bookFile.get();
}
/// Book::read_entry() takes an integer index, and returns the BookEntry
/// at the given index in the book file.
@ -514,7 +526,10 @@ BookEntry Book::read_entry(int idx) {
bookFile.seekg(idx * sizeof(BookEntry), ios_base::beg);
*this >> e.key >> e.move >> e.count >> e.learn;
get_number(e.key);
get_number(e.move);
get_number(e.count);
get_number(e.learn);
if (!bookFile.good())
{

11
src/book.h
View file

@ -48,12 +48,7 @@ public:
const std::string name() const { return bookName; }
private:
// read n chars from the file stream and converts them in an
// integer number. Integers are stored with highest byte first.
template<int n> uint64_t get_int();
template<typename T>
Book& operator>>(T& n) { n = (T)get_int<sizeof(T)>(); return *this; }
template<typename T> void get_number(T& n);
BookEntry read_entry(int idx);
int find_entry(uint64_t key);
@ -64,8 +59,4 @@ private:
RKISS RKiss;
};
// Yes, we indulge a bit here ;-)
template<int n> inline uint64_t Book::get_int() { return 256 * get_int<n-1>() + bookFile.get(); }
template<> inline uint64_t Book::get_int<1>() { return bookFile.get(); }
#endif // !defined(BOOK_H_INCLUDED)