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QLocale/Win: replace hand-written binary search with a call to lower_bound() 

Binary search is notoriously hard to implement, and, while I didn't
spend time to prove it, this implementation was probably buggy, too
(any implementation which is missing a ±1 in the loop body is
suspicious).

Replace with a call to std::lower_bound(), which has precise semantics
and no bugs.

Task-number: QTBUG-103721
Change-Id: Ibe12c7d20b8c01e19a6f294f6c1b564b6b484b07
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
bb10
Marc Mutz 2022-07-18 11:48:55 +02:00
parent 25de37381d
commit 424438a220
1 changed files with 10 additions and 18 deletions
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28
src/corelib/text/qlocale_win.cpp
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@ -892,6 +892,10 @@ struct WindowsToISOListElt {
namespace {
struct ByWindowsCode {
constexpr bool operator()(int lhs, WindowsToISOListElt rhs) const noexcept
{ return lhs < int(rhs.windows_code); }
constexpr bool operator()(WindowsToISOListElt lhs, int rhs) const noexcept
{ return int(lhs.windows_code) < rhs; }
constexpr bool operator()(WindowsToISOListElt lhs, WindowsToISOListElt rhs) const noexcept
{ return lhs.windows_code < rhs.windows_code; }
};
@ -1008,9 +1012,6 @@ static constexpr WindowsToISOListElt windows_to_iso_list[] = {
{ 0x500a, "es_PR" }
};
static const int windows_to_iso_count
= sizeof(windows_to_iso_list)/sizeof(WindowsToISOListElt);
static_assert(q20::is_sorted(std::begin(windows_to_iso_list), std::end(windows_to_iso_list),
ByWindowsCode{}));
@ -1023,21 +1024,12 @@ static const char *winLangCodeToIsoName(int code)
if (cmp == 0)
return windows_to_iso_list[0].iso_name;
int begin = 0;
int end = windows_to_iso_count;
while (end - begin > 1) {
uint mid = (begin + end)/2;
const WindowsToISOListElt *elt = windows_to_iso_list + mid;
int cmp = code - elt->windows_code;
if (cmp < 0)
end = mid;
else if (cmp > 0)
begin = mid;
else
return elt->iso_name;
}
const auto it = std::lower_bound(std::begin(windows_to_iso_list),
std::end(windows_to_iso_list),
code,
ByWindowsCode{});
if (it != std::end(windows_to_iso_list) && !ByWindowsCode{}(code, *it))
return it->iso_name;
return 0;