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Utils: Simplify SmallString reserve

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The reserve function is quite complicated because it is implementing a
grow pattern. Something we seldom need. So we now align to the next cache
line size.

Change-Id: I14bb88c12bd740a7afa7cd08969a4e07fb0f9add
Reviewed-by: Tim Jenssen <tim.jenssen@qt.io>
This commit is contained in:
Marco Bubke
2017-09-14 11:48:17 +02:00
parent e255baaa8f
commit 76a7dff82b
2 changed files with 6 additions and 15 deletions
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13
src/libs/utils/smallstring.h
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@@ -658,18 +658,9 @@ unittest_public:
{ {
const size_type cacheLineSize = 64; const size_type cacheLineSize = 64;
const auto divisionByCacheLineSize = std::div(int64_t(size), int64_t(cacheLineSize)); size_type cacheLineBlocks = (size - 1) / cacheLineSize;
size_type cacheLineBlocks = size_type(divisionByCacheLineSize.quot); return (cacheLineBlocks + 1) * cacheLineSize;
const size_type supplement = divisionByCacheLineSize.rem ? 1 : 0;
cacheLineBlocks += supplement;
int exponent;
const double significand = std::frexp(cacheLineBlocks, &exponent);
const double factorOneDotFiveSignificant = std::ceil(significand * 4.) / 4.;
cacheLineBlocks = size_type(std::ldexp(factorOneDotFiveSignificant, exponent));
return cacheLineBlocks * cacheLineSize;
} }
size_type countOccurrence(SmallStringView text) size_type countOccurrence(SmallStringView text)

8
tests/unit/unittest/smallstring-test.cpp
View File

@@ -1067,13 +1067,13 @@ TEST(SmallString, OptimalHeapCacheLineForSize)
ASSERT_THAT(SmallString::optimalHeapCapacity(191), 192); ASSERT_THAT(SmallString::optimalHeapCapacity(191), 192);
ASSERT_THAT(SmallString::optimalHeapCapacity(193), 256); ASSERT_THAT(SmallString::optimalHeapCapacity(193), 256);
ASSERT_THAT(SmallString::optimalHeapCapacity(255), 256); ASSERT_THAT(SmallString::optimalHeapCapacity(255), 256);
ASSERT_THAT(SmallString::optimalHeapCapacity(257), 384); ASSERT_THAT(SmallString::optimalHeapCapacity(256), 256);
ASSERT_THAT(SmallString::optimalHeapCapacity(257), 384); ASSERT_THAT(SmallString::optimalHeapCapacity(257), 320);
ASSERT_THAT(SmallString::optimalHeapCapacity(383), 384); ASSERT_THAT(SmallString::optimalHeapCapacity(383), 384);
ASSERT_THAT(SmallString::optimalHeapCapacity(385), 512); ASSERT_THAT(SmallString::optimalHeapCapacity(385), 448);
ASSERT_THAT(SmallString::optimalHeapCapacity(4095), 4096); ASSERT_THAT(SmallString::optimalHeapCapacity(4095), 4096);
ASSERT_THAT(SmallString::optimalHeapCapacity(4096), 4096); ASSERT_THAT(SmallString::optimalHeapCapacity(4096), 4096);
ASSERT_THAT(SmallString::optimalHeapCapacity(4097), 6144); ASSERT_THAT(SmallString::optimalHeapCapacity(4097), 4160);
} }
TEST(SmallString, OptimalCapacityForSize) TEST(SmallString, OptimalCapacityForSize)