[Issue 6445] New: [CTFE] Absurd memory usage (still) on building array

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=6445

           Summary: [CTFE] Absurd memory usage (still) on building array
           Product: D
           Version: unspecified
          Platform: Other
        OS/Version: Windows
            Status: NEW
          Keywords: performance
          Severity: normal
          Priority: P2
         Component: DMD
        AssignedTo: nobody at puremagic.com
        ReportedBy: dsimcha at yahoo.com


--- Comment #0 from David Simcha <dsimcha at yahoo.com> 2011-08-06 13:34:11 PDT ---
The following program uses over a gigabyte of memory at compile time.  I
thought these kinds of issues were fixed by the rewrite of CTFE in the last
release.

enum staticFacTableLen = 1000;
immutable table = makeLogFacTable();

immutable(double[staticFacTableLen]) makeLogFacTable() pure nothrow {

    static real log(real x) pure nothrow @safe
    {
        immutable xMinusPlus = (x - 1) / (x + 1);
        immutable xMinusPlusSquared = xMinusPlus * xMinusPlus;
        real xMinusPlusPow = xMinusPlus * xMinusPlusSquared;

        real ret = xMinusPlus;
        real power = 3;

        while(true)
        {
            immutable toAdd = xMinusPlusPow / power;
            immutable oldRet = ret;
            ret += toAdd;

            if(ret == oldRet || ret != ret)
            {
                return 2 * ret;
            }

            power += 2;
            xMinusPlusPow *= xMinusPlusSquared;
        }

        assert(0);
    }

    double[staticFacTableLen] ret;

    ret[0] = 0;
    foreach(i; 1..staticFacTableLen) {
        ret[i] = ret[i - 1] + log(i);
    }

    return cast(immutable) ret;
}

-- 
Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email
------- You are receiving this mail because: -------