return sp;
}
+namespace {
+
+void toLowerAscii8(char& c) {
+ // Branchless tolower, based on the input-rotating trick described
+ // at http://www.azillionmonkeys.com/qed/asmexample.html
+ //
+ // This algorithm depends on an observation: each uppercase
+ // ASCII character can be converted to its lowercase equivalent
+ // by adding 0x20.
+
+ // Step 1: Clear the high order bit. We'll deal with it in Step 5.
+ unsigned char rotated = c & 0x7f;
+ // Currently, the value of rotated, as a function of the original c is:
+ // below 'A': 0- 64
+ // 'A'-'Z': 65- 90
+ // above 'Z': 91-127
+
+ // Step 2: Add 0x25 (37)
+ rotated += 0x25;
+ // Now the value of rotated, as a function of the original c is:
+ // below 'A': 37-101
+ // 'A'-'Z': 102-127
+ // above 'Z': 128-164
+
+ // Step 3: clear the high order bit
+ rotated &= 0x7f;
+ // below 'A': 37-101
+ // 'A'-'Z': 102-127
+ // above 'Z': 0- 36
+
+ // Step 4: Add 0x1a (26)
+ rotated += 0x1a;
+ // below 'A': 63-127
+ // 'A'-'Z': 128-153
+ // above 'Z': 25- 62
+
+ // At this point, note that only the uppercase letters have been
+ // transformed into values with the high order bit set (128 and above).
+
+ // Step 5: Shift the high order bit 2 spaces to the right: the spot
+ // where the only 1 bit in 0x20 is. But first, how we ignored the
+ // high order bit of the original c in step 1? If that bit was set,
+ // we may have just gotten a false match on a value in the range
+ // 128+'A' to 128+'Z'. To correct this, need to clear the high order
+ // bit of rotated if the high order bit of c is set. Since we don't
+ // care about the other bits in rotated, the easiest thing to do
+ // is invert all the bits in c and bitwise-and them with rotated.
+ rotated &= ~c;
+ rotated >>= 2;
+
+ // Step 6: Apply a mask to clear everything except the 0x20 bit
+ // in rotated.
+ rotated &= 0x20;
+
+ // At this point, rotated is 0x20 if c is 'A'-'Z' and 0x00 otherwise
+
+ // Step 7: Add rotated to c
+ c += rotated;
+}
+
+void toLowerAscii32(uint32_t& c) {
+ // Besides being branchless, the algorithm in toLowerAscii8() has another
+ // interesting property: None of the addition operations will cause
+ // an overflow in the 8-bit value. So we can pack four 8-bit values
+ // into a uint32_t and run each operation on all four values in parallel
+ // without having to use any CPU-specific SIMD instructions.
+ uint32_t rotated = c & uint32_t(0x7f7f7f7fL);
+ rotated += uint32_t(0x25252525L);
+ rotated &= uint32_t(0x7f7f7f7fL);
+ rotated += uint32_t(0x1a1a1a1aL);
+
+ // Step 5 involves a shift, so some bits will spill over from each
+ // 8-bit value into the next. But that's okay, because they're bits
+ // that will be cleared by the mask in step 6 anyway.
+ rotated &= ~c;
+ rotated >>= 2;
+ rotated &= uint32_t(0x20202020L);
+ c += rotated;
+}
+
+void toLowerAscii64(uint64_t& c) {
+ // 64-bit version of toLower32
+ uint64_t rotated = c & uint64_t(0x7f7f7f7f7f7f7f7fL);
+ rotated += uint64_t(0x2525252525252525L);
+ rotated &= uint64_t(0x7f7f7f7f7f7f7f7fL);
+ rotated += uint64_t(0x1a1a1a1a1a1a1a1aL);
+ rotated &= ~c;
+ rotated >>= 2;
+ rotated &= uint64_t(0x2020202020202020L);
+ c += rotated;
+}
+
+} // anon namespace
+
+void toLowerAscii(char* str, size_t length) {
+ static const size_t kAlignMask64 = 7;
+ static const size_t kAlignMask32 = 3;
+
+ // Convert a character at a time until we reach an address that
+ // is at least 32-bit aligned
+ size_t n = (size_t)str;
+ n &= kAlignMask32;
+ n = std::min(n, length);
+ size_t offset = 0;
+ if (n != 0) {
+ do {
+ toLowerAscii8(str[offset]);
+ offset++;
+ } while (offset < n);
+ }
+
+ n = (size_t)(str + offset);
+ n &= kAlignMask64;
+ if ((n != 0) && (offset + 4 < length)) {
+ // The next address is 32-bit aligned but not 64-bit aligned.
+ // Convert the next 4 bytes in order to get to the 64-bit aligned
+ // part of the input.
+ toLowerAscii32(*(uint32_t*)(str + offset));
+ offset += 4;
+ }
+
+ // Convert 8 characters at a time
+ while (offset + 8 < length) {
+ toLowerAscii64(*(uint64_t*)(str + offset));
+ offset += 8;
+ }
+
+ // Convert 4 characters at a time
+ while (offset + 4 < length) {
+ toLowerAscii32(*(uint32_t*)(str + offset));
+ offset += 4;
+ }
+
+ // Convert any characters remaining after the last 4-byte aligned group
+ while (offset < length) {
+ toLowerAscii8(str[offset]);
+ offset++;
+ }
+}
+
namespace detail {
size_t hexDumpLine(const void* ptr, size_t offset, size_t size,
*/
StringPiece skipWhitespace(StringPiece sp);
+/**
+ * Fast, in-place lowercasing of ASCII alphabetic characters in strings.
+ * Leaves all other characters unchanged, including those with the 0x80
+ * bit set.
+ * @param str String to convert
+ * @param len Length of str, in bytes
+ */
+void toLowerAscii(char* str, size_t length);
+
+inline void toLowerAscii(MutableStringPiece str) {
+ toLowerAscii(str.begin(), str.size());
+}
+
} // namespace folly
// Hash functions to make std::string usable with e.g. hash_map
--- /dev/null
+/*
+ * Copyright 2014 Facebook, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/Benchmark.h>
+#include <folly/String.h>
+
+BENCHMARK(libc_tolower, iters) {
+ static const size_t kSize = 256;
+ // This array is static to keep the compiler from optimizing the
+ // entire function down to a no-op if it has an inlined impl of
+ // tolower and thus is able to tell that there are no side-effects.
+ // No side-effects + no writes to anything other than local variables
+ // + no return value = no need to run any of the code in the function.
+ // gcc, for example, makes that optimization with -O2.
+ static char input[kSize];
+ for (size_t i = 0; i < kSize; i++) {
+ input[i] = (char)(i & 0xff);
+ }
+ for (auto i = iters; i > 0; i--) {
+ for (size_t offset = 0; offset < kSize; offset++) {
+ input[offset] = tolower(input[offset]);
+ }
+ }
+}
+
+BENCHMARK(folly_toLowerAscii, iters) {
+ static const size_t kSize = 256;
+ static char input[kSize];
+ for (size_t i = 0; i < kSize; i++) {
+ input[i] = (char)(i & 0xff);
+ }
+ for (auto i = iters; i > 0; i--) {
+ folly::toLowerAscii(input, kSize);
+ }
+}
+
+int main(int argc, char** argv) {
+ google::ParseCommandLineFlags(&argc, &argv, true);
+ folly::runBenchmarks();
+ if (FLAGS_benchmark) {
+ folly::runBenchmarks();
+ }
+ return 0;
+}
+
+/*
+Results on x86_64:
+============================================================================
+folly/test/StringBenchmark.cpp relative time/iter iters/s
+============================================================================
+libc_tolower 1.30us 767.50K
+folly_toLowerAscii 115.21ns 8.68M
+============================================================================
+*/
EXPECT_EQ("0x61ffffffffff", humanify(string("a\xff\xff\xff\xff\xff")));
}
+namespace {
+
+void testToLowerAscii(Range<const char*> src) {
+ char control[src.size()];
+ memcpy(control, src.begin(), src.size());
+ char test[src.size()];
+ memcpy(test, src.begin(), src.size());
+ for (size_t i = 0; i < src.size(); i++) {
+ control[i] = tolower(control[i]);
+ }
+ toLowerAscii(test, src.size());
+ for (size_t i = 0; i < src.size(); i++) {
+ EXPECT_EQ(control[i], test[i]);
+ }
+}
+
+} // anon namespace
+
+TEST(String, toLowerAsciiAligned) {
+ static const size_t kSize = 256;
+ char input[kSize];
+ for (size_t i = 0; i < kSize; i++) {
+ input[i] = (char)(i & 0xff);
+ }
+ testToLowerAscii(Range<const char*>(input, kSize));
+}
+
+TEST(String, toLowerAsciiUnaligned) {
+ static const size_t kSize = 256;
+ char input[kSize];
+ for (size_t i = 0; i < kSize; i++) {
+ input[i] = (char)(i & 0xff);
+ }
+ // Test input buffers of several lengths to exercise all the
+ // cases: buffer at the start/middle/end of an aligned block, plus
+ // buffers that span multiple aligned blocks.
+ for (size_t length = 1; length < 11; length++) {
+ for (size_t offset = 0; offset + length <= kSize; offset++) {
+ testToLowerAscii(Range<const char*>(input + offset, length));
+ }
+ }
+}
+
//////////////////////////////////////////////////////////////////////
BENCHMARK(splitOnSingleChar, iters) {
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