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root/software/lowercase_util/lowercase_util.cc @ 11ae9ac5

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#include <cctype>
#include <chrono>
#include <cstdint>
#include <fstream>
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#include <ios>
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#include <iostream>
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#include <iomanip>
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#include <string>
#include <vector>

#include <sys/types.h>
#include <sys/stat.h>

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#include <x86intrin.h>

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// https://stackoverflow.com/questions/3883993/how-could-these-case-conversion-functions-be-improved
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inline void SIMD_128_tolower(char* inputData, uint64_t length)
{
const __m128i data_65 = _mm_set1_epi8(65); // 'A'
const __m128i data_26 = _mm_set1_epi8(26);
const __m128i data_32 = _mm_set1_epi8(32);
const __m128i clear_msb = _mm_set1_epi8(0x7F);
char *dataPtr = inputData;
char *dataStop = inputData + length;
while (dataPtr < dataStop)
{
// Load data
__m128i data = _mm_lddqu_si128(reinterpret_cast<__m128i *>(dataPtr));

// Load copy of data into working register
__m128i work_reg = _mm_lddqu_si128(&data);
// Subtract 'A' from working register
work_reg = _mm_sub_epi8(work_reg, data_65);
// AND together packed "clear MSB" to simulate the cast to unsigned
work_reg = _mm_and_si128(work_reg, clear_msb);
// Compare work register less than 26 and store in work register
work_reg = _mm_cmplt_epi8(work_reg, data_26);
// AND together packed 32 data and work regiser
work_reg = _mm_and_si128(work_reg, data_32);
// Accumulate with work register
data = _mm_add_epi8(data, work_reg);
// Store converted values back to array
_mm_storeu_si128(reinterpret_cast<__m128i *>(dataPtr), data);
// Advance data pointer
dataPtr += 16;
}
}

inline void SIMD_256_tolower(char* inputData, uint64_t length)
{
const __m256i data_65 = _mm256_set1_epi8(65); // 'A'
const __m256i data_26 = _mm256_set1_epi8(26);
const __m256i data_32 = _mm256_set1_epi8(32);
const __m256i clear_msb = _mm256_set1_epi8(0x7F);
char *dataPtr = inputData;
char *dataStop = inputData + length;
while (dataPtr < dataStop)
{
// Load data
__m256i data = _mm256_lddqu_si256(reinterpret_cast<__m256i *>(dataPtr));
// Load copy of data into working register
__m256i work_reg = _mm256_lddqu_si256(&data);
// Subtract 'A' from working register
work_reg = _mm256_sub_epi8(work_reg, data_65);
// AND together packed "clear MSB" to simulate the cast to unsigned
work_reg = _mm256_and_si256(work_reg, clear_msb);
// Compare 26 greater than work registerand store in work register
// NOTE: AVX2 does not have cmplt intrinsic so compare is inverted
work_reg = _mm256_cmpgt_epi8(data_26, work_reg);
// AND together packed 32 data and work regiser
work_reg = _mm256_and_si256(work_reg, data_32);
// Accumulate with work register
data = _mm256_add_epi8(data, work_reg);
// Store converted values back to array
_mm256_storeu_si256(reinterpret_cast<__m256i *>(dataPtr), data);
// Advance data pointer
dataPtr += 32;
}
}

inline uint64_t align16(uint64_t size)
{
return (size & 0xF) ? ((size + 0x10) & ~(0xF)) : size;
}

inline uint64_t align32(uint64_t size)
{
return (size & 0x1F) ? ((size + 0x20) & ~(0x1F)) : size;
}
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inline double speedup(double old, double new_)
{
return (((old / new_) - 1) * 100);
}


// g++ -std=c++11 -O3 -msse2 lowercase_util.cc -o lowercase_util
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int main(const int argc, char** argv)
{
if (argc < 2)
{
std::cerr << "USAGE: " << argv[0] << " <filename>" << std::endl;
return -1;
}
std::cout << "Lowercase Test Util\n" << std::endl;
std::string filePath(argv[1]);

// Stat the file path to get its size
struct stat fs_stat;
const int gotStatOK(stat(filePath.c_str(), &fs_stat));
if (gotStatOK < 0)
{
perror("stat()");
return -1;
}

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uint64_t fileSize = fs_stat.st_size;
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std::cout << "File size: " << fileSize << "\n" << std::endl;
// Read in file
std::ifstream inFileStream(filePath, std::ios::in | std::ios::binary);
if (! inFileStream)
{
std::cerr << "Unable to open specified file." << std::endl;
return -1;
}
// Read file in then close stream
std::vector<char> contents;
contents.resize(fileSize);
inFileStream.read(contents.data(), fileSize);
inFileStream.close();
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// TEST1: regular standard library tolower() ------------------------------
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std::vector<char> copy1(contents);
auto start = std::chrono::system_clock::now();
for (uint32_t idx = 0; idx < fileSize; ++idx)
{
copy1[idx] = tolower(copy1[idx]);
}
auto end = std::chrono::system_clock::now();
auto diff = end - start;
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double test1_duration = std::chrono::duration<double, std::milli>(diff).count();
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std::cout << "Test 1: STD lib tolower() -- duration: "
<< std::setw(10) << std::fixed << std::setprecision(3) << test1_duration
<< " ms -- " << std::fixed << std::setprecision(2) << std::setw(7)
<< speedup(test1_duration, test1_duration) << "%" << std::endl;


// TEST2: bit twiddle with comparison -------------------------------------
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std::vector<char> copy2(contents);
start = std::chrono::system_clock::now();
for (uint32_t idx = 0; idx < fileSize; ++idx)
{
// *c += (*c - 'A' < 26U) << 5;
copy2[idx] += (copy2[idx] - 'A' < 26U) << 5;
}
end = std::chrono::system_clock::now();
diff = end - start;
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double test2_duration = std::chrono::duration<double, std::milli>(diff).count();
std::cout << "Test 2: bit twiddle with comparison -- duration: "
<< std::setw(10) << std::fixed << std::setprecision(3) << test2_duration
<< " ms -- " << std::fixed << std::setprecision(2) << std::setw(7)
<< speedup(test1_duration, test2_duration) << "%" << std::endl;
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#if 0
// Verify copy2
std::ofstream outStream1("output_copy2.txt", std::ios::out | std::ios::binary);
outStream1.write(copy2.data(), fileSize);
outStream1.close();
#endif
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// TEST3: bit twiddle with no comparison ----------------------------------
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std::vector<char> copy3(contents);
start = std::chrono::system_clock::now();
for (uint32_t idx = 0; idx < fileSize; ++idx)
{
// *c += (64U - *c & *c - 91U) >> CHAR_BIT * sizeof(unsigned) - 1 << 5;
// *c += ((64U - *c & *c - 91U) >> 31) << 5;
copy3[idx] += ((64U - copy3[idx] & copy3[idx] - 91U) >> 31) << 5;
}
end = std::chrono::system_clock::now();
diff = end - start;
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double test3_duration = std::chrono::duration<double, std::milli>(diff).count();
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std::cout << "Test 3: bit twiddle w/ no comparison -- duration: "
<< std::setw(10) << std::fixed << std::setprecision(3) << test3_duration
<< " ms -- " << std::fixed << std::setprecision(2) << std::setw(7)
<< speedup(test1_duration, test3_duration) << "%" << std::endl;
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// TEST 4: alternate bit twiddle with no comparison -----------------------
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std::vector<char> copy4(contents);
start = std::chrono::system_clock::now();
for (uint32_t idx = 0; idx < fileSize; ++idx)
{
// c += (((96-(int)c)&((int)c-123))>>9)&(-32);
copy4[idx] += (((96 - (int)copy4[idx]) & ((int)copy4[idx] - 123)) >> 9) & (-32);
}
end = std::chrono::system_clock::now();
diff = end - start;
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double test4_duration = std::chrono::duration<double, std::milli>(diff).count();
std::cout << "Test 4: bit twiddle w/ no comp alt -- duration: "
<< std::setw(10) << std::fixed << std::setprecision(3) << test4_duration
<< " ms -- " << std::fixed << std::setprecision(2) << std::setw(7)
<< speedup(test1_duration, test4_duration) << "%" << std::endl;

// TEST 5: optimized SIMD (16 bytes at a time) ----------------------------
std::vector<char> copy5(contents);
// NOTE: data buffer size MUST be 16 byte aligned
copy5.reserve(align16(fileSize));
start = std::chrono::system_clock::now();
SIMD_128_tolower(copy5.data(), fileSize);
end = std::chrono::system_clock::now();
diff = end - start;
double test5_duration = std::chrono::duration<double, std::milli>(diff).count();
std::cout << "Test 5: optimized SIMD 128 bit (16 byte) -- duration: "
<< std::setw(10) << std::fixed << std::setprecision(3) << test5_duration
<< " ms -- " << std::fixed << std::setprecision(2) << std::setw(7)
<< speedup(test1_duration, test5_duration) << "%" << std::endl;
// TEST 6: optimized SIMD (32 bytes at a time) ----------------------------
std::vector<char> copy6(contents);
// NOTE: data buffer size MUST be 32 byte aligned
copy6.reserve(align32(fileSize));
start = std::chrono::system_clock::now();
SIMD_256_tolower(copy6.data(), fileSize);
end = std::chrono::system_clock::now();
diff = end - start;
double test6_duration = std::chrono::duration<double, std::milli>(diff).count();
std::cout << "Test 6: optimized SIMD 256 bit (32 byte) -- duration: "
<< std::setw(10) << std::fixed << std::setprecision(3) << test6_duration
<< " ms -- " << std::fixed << std::setprecision(2) << std::setw(7)
<< speedup(test1_duration, test6_duration) << "%" << std::endl;

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return 0;
}