Ticket #3368: maths.patch

Sqrt.cpp

@@ -19 +19 @@
 
 #include "Sqrt.h"
 
+#if !(defined(_MSC_VER) || defined(__GNUC__) || defined(__clang__))
+
+// NOTE: this handwritten sqrt function has been found to be much slower than the 
+// one provided by the standard library on the MSVC, GCC and Clang compilers on
+// x86 and x86-64 architectures. Other compilers and architectures have not been 
+// tested but the performance penalty is likely to be comparable.
+
 // Based on http://freaknet.org/martin/tape/gos/misc/personal/msc/sqrt/sqrt.html
 u32 isqrt64(u64 n)
 {
@@ -42 +49 @@
     return (u32)res;
 }
 
-// TODO: This should be equivalent to (u32)sqrt((double)n), and in practice
-// that seems to be true for all input, so do we actually need this integer-only
-// implementation? i.e. are there any platforms / compiler settings where
-// sqrt(double) won't give the correct answer? and is sqrt(double) faster?
+#endif

Sqrt.h

@@ -22 +22 @@
  * 64-bit integer square root.
  * Returns r such that r^2 <= n < (r+1)^2, for the complete u64 range.
  */
+//NOTE: see Sqrt.cpp note
+#if defined(_MSC_VER) || defined(__GNUC__) || defined(__clang__)
+
+#include <cmath>
+inline u32 isqrt64(u64 n) { return (u32)sqrt((double)n); }
+
+#else
+
 u32 isqrt64(u64 n);
 
+#endif
+
 #endif // INCLUDED_MATH_SQRT