Intrinsic 2 solution

labs/core_bound/compiler_intrinsics_2/solution.cpp

@@ -1,6 +1,62 @@
 #include "solution.hpp"
+
+#define SOLUTION
+#if defined(SOLUTION) && defined(__AVX2__)
+
+#include <immintrin.h>
 #include <iostream>
+#include <cassert>
+
+unsigned solution(const std::string &inputContents)
+{
+  constexpr int avx_char_num = 256 / 8;
+
+  unsigned longestLine = 0;
+  unsigned curLineLength = 0;
+
+  int i = 0;
+  const int char_num = inputContents.size();
+
+  const __m256i newline = _mm256_set1_epi8('\n');
+  const char *chars_in = inputContents.data();
+  for (; i < char_num - avx_char_num; i += avx_char_num)
+  {
+    const __m256i chars = _mm256_loadu_si256((__m256i *)(chars_in + i));
+    const __m256i cmp_mask256 = _mm256_cmpeq_epi8(chars, newline);
+    int cmp_mask = _mm256_movemask_epi8(cmp_mask256);
+
+    int internal_pos = 0;
+
+    while (cmp_mask)
+    {
+      const unsigned int leading_zeros = _tzcnt_u32(cmp_mask);
+      curLineLength += leading_zeros;
+      longestLine = std::max(curLineLength, longestLine);
+      curLineLength = 0;
+      internal_pos += leading_zeros + 1;
+      if (internal_pos > 31)
+      {
+        // 32 >= shifts are UB (also that means we processed the entire word)
+        break;
+      }
+      cmp_mask >>= leading_zeros + 1;
+    }
+
+    curLineLength += 32 - internal_pos;
+  }
+  longestLine = std::max(curLineLength, longestLine);
+
+  for (; i < char_num; ++i)
+  {
+    auto s = inputContents[i];
+    curLineLength = (s == '\n') ? 0 : curLineLength + 1;
+    longestLine = std::max(curLineLength, longestLine);
+  }
+
+  return longestLine;
+}
 
+#else
 // Find the longest line in a file.
 // Implementation uses ternary operator with a hope that compiler will
 // turn it into a CMOV instruction.
@@ -12,14 +68,17 @@ if (s == '\n') {
 } else {
   curLineLength++;
 }*/
-unsigned solution(const std::string &inputContents) {
+unsigned solution(const std::string &inputContents)
+{
   unsigned longestLine = 0;
   unsigned curLineLength = 0;
 
-  for (auto s : inputContents) {
+  for (auto s : inputContents)
+  {
     curLineLength = (s == '\n') ? 0 : curLineLength + 1;
     longestLine = std::max(curLineLength, longestLine);
   }
 
   return longestLine;
 }
+#endif