Merge pull request #16809 from kitaisreal/read-float-8digits-unroll-performance-improvement

ReadFloat 8digits unroll performance improvement

src/IO/readFloatText.h

@@ -249,6 +249,19 @@ ReturnType readFloatTextPreciseImpl(T & x, ReadBuffer & buf)
 }
 
 
+// credit: https://johnnylee-sde.github.io/Fast-numeric-string-to-int/
+static inline bool is_made_of_eight_digits_fast(uint64_t val) noexcept
+{
+    return (((val & 0xF0F0F0F0F0F0F0F0) | (((val + 0x0606060606060606) & 0xF0F0F0F0F0F0F0F0) >> 4)) == 0x3333333333333333);
+}
+
+static inline bool is_made_of_eight_digits_fast(const char * chars) noexcept
+{
+    uint64_t val;
+    ::memcpy(&val, chars, 8);
+    return is_made_of_eight_digits_fast(val);
+}
+
 template <size_t N, typename T>
 static inline void readUIntTextUpToNSignificantDigits(T & x, ReadBuffer & buf)
 {
@@ -266,9 +279,6 @@ static inline void readUIntTextUpToNSignificantDigits(T & x, ReadBuffer & buf)
             else
                 return;
         }
-
-        while (!buf.eof() && isNumericASCII(*buf.position()))
-            ++buf.position();
     }
     else
     {
@@ -283,10 +293,16 @@ static inline void readUIntTextUpToNSignificantDigits(T & x, ReadBuffer & buf)
             else
                 return;
         }
-
-        while (!buf.eof() && isNumericASCII(*buf.position()))
-            ++buf.position();
     }
+
+    while (!buf.eof() && (buf.position() + 8 <= buf.buffer().end()) &&
+         is_made_of_eight_digits_fast(buf.position()))
+    {
+        buf.position() += 8;
+    }
+
+    while (!buf.eof() && isNumericASCII(*buf.position()))
+        ++buf.position();
 }
 
 
@@ -319,7 +335,6 @@ ReturnType readFloatTextFastImpl(T & x, ReadBuffer & in)
         ++in.position();
     }
 
-
     auto count_after_sign = in.count();
 
     constexpr int significant_digits = std::numeric_limits<UInt64>::digits10;