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QColor: avoid Unicode table lookups in fromString() 

All color names supported by QColor are US-ASCII.

Enforce this with a static_assert, then use this fact to perform the
case-folding of the input in US-ASCII instead of Unicode.

Avoids lookups in the Unicode tables.

Add QtMiscUtils::toAsciiLower() to foster sharing.

Change-Id: Ie0e123405d772943313dc4be1808667b152770b1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
bb10
Marc Mutz 2022-02-16 07:00:05 +01:00
parent 795c94658d
commit 5f338040f4
2 changed files with 20 additions and 4 deletions
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5
src/corelib/tools/qtools_p.h
View File

@ -84,6 +84,11 @@ constexpr inline int fromOct(uint c) noexcept
{
return ((c >= '0') && (c <= '7')) ? int(c - '0') : -1;
}
constexpr inline char toAsciiLower(char ch) noexcept
{
return (ch >= 'A' && ch <= 'Z') ? ch - 'A' + 'a' : ch;
}
}
// We typically need an extra bit for qNextPowerOfTwo when determining the next allocation size.

19
src/gui/painting/qcolor.cpp
View File

@ -164,7 +164,7 @@ static bool get_hex_rgb(QAnyStringView name, QRgba64 *rgb)
#define rgb(r,g,b) (0xff000000 | (r << 16) | (g << 8) | b)
// keep this is in sync with QColorConstants
static const struct RGBData {
static constexpr struct RGBData {
const char name[21];
uint value;
} rgbTbl[] = {
@ -320,6 +320,16 @@ static const struct RGBData {
static const int rgbTblSize = sizeof(rgbTbl) / sizeof(RGBData);
static_assert([] {
for (auto e : rgbTbl) {
for (auto it = e.name; *it ; ++it) {
if (uchar(*it) > 127)
return false;
}
}
return true;
}(), "the lookup code expects color names to be US-ASCII-only");
#undef rgb
inline bool operator<(const char *name, const RGBData &data)
@ -338,8 +348,9 @@ static bool get_named_rgb_no_space(const char *name_no_space, QRgb *rgb)
}
namespace {
static inline char toLower(QChar ch) noexcept { return ch.toLower().toLatin1(); }
static inline char toLower(char ch) noexcept { return toLower(QLatin1Char{ch}); }
// named colors are US-ASCII (enforced by static_assert above):
static char to_char(char ch) noexcept { return ch; }
static char to_char(QChar ch) noexcept { return ch.toLatin1(); }
}
static bool get_named_rgb(QAnyStringView name, QRgb* rgb)
@ -351,7 +362,7 @@ static bool get_named_rgb(QAnyStringView name, QRgb* rgb)
name.visit([&pos, &name_no_space] (auto name) {
for (auto c : name) {
if (c != u'\t' && c != u' ')
name_no_space[pos++] = toLower(c);
name_no_space[pos++] = QtMiscUtils::toAsciiLower(to_char(c));
}
});
name_no_space[pos] = 0;