• downs <default_357-line yahoo.de> Nov 13 2007
• Bill Baxter <dnewsgroup billbaxter.com> Nov 13 2007
• downs <default_357-line yahoo.de> Nov 13 2007

I'm seeing huge speed-ups in a benchmark between std.math's sqrt and

 import gcc.builtins;
 real sqrt(real r) { return __builtin_sqrtl(r); }.


I presume this is because GDC's std.math uses library functions, which become
function
calls; whereas __builtin_sqrtl is compiled as a single assembler instruction.

Is there any specific reason why GDC's current std.math does not take advantage
of GCC's
built-in functions?

If there isn't, I'd suggest std.math be changed to call these functions instead,
which could lead to significant speed gains in math-heavy programs.

See also: http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Other-Builtins.html#Other-Builtins

Looking forward to opinions/explanations,
 --downs

downs wrote:
 I'm seeing huge speed-ups in a benchmark between std.math's sqrt and
 
 import gcc.builtins;
 real sqrt(real r) { return __builtin_sqrtl(r); }.


 I presume this is because GDC's std.math uses library functions, which become
function
 calls; whereas __builtin_sqrtl is compiled as a single assembler instruction.
 
 Is there any specific reason why GDC's current std.math does not take
advantage of GCC's
 built-in functions?
 
 If there isn't, I'd suggest std.math be changed to call these functions
instead,
 which could lead to significant speed gains in math-heavy programs.
 
 See also: http://gcc.gnu.org/onlinedocs/gcc-4.1.2/gcc/Other-Builtins.html#Other-Builtins
 
 Looking forward to opinions/explanations,
  --downs


So was that the main culprit for the slowdowns in your raytracer test?

--bb

Bill Baxter wrote:
 So was that the main culprit for the slowdowns in your raytracer test?
 
 --bb


Nope, afraid not. Would have been nice though :)
 --downs, still clueless about gdc performance