http://d.puremagic.com/issues/show_bug.cgi?id=3162

           Summary: can't fully use floats computed in CTFE as template
                    parameters
           Product: D
           Version: 2.028
          Platform: Other
        OS/Version: Linux
            Status: NEW
          Keywords: rejects-valid
          Severity: major
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: baryluk@smp.if.uj.edu.pl


/** Computes square root at compile time */
real ctfe_sqrt(real x) {
  real root = x / 2.0;
  for (int ntries = 0; ntries < 10; ntries++) {
    if (root * root - x == 0)
      break;
    root = (root + x / root) / 2.0;
  }
  return root;
}

/** Square root of 2 */
static const double sqrt2 = ctfe_sqrt(2.0);
import std.metastrings;
pragma(msg, Format!("s=", cast(int)(1000*sqrt2))); // works


pragma(msg, Format!("s=", cast(int)(1000*sqrt2), " ", cast(int)(1000*sqrt2), "
")); // doesn't work
//pragma(msg, Format!("s=", cast(int)(1000*sqrt2))); // also doesn't work

pragma(msg, Format!("s=", cast(int)((1.0+sqrt2/2.0))); // doesn't works



Looks that only first occurence of value derived from constant derived using ctfs can be used.

It was working in some older releases.

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--- Comment #1 from Witold Baryluk <baryluk@smp.if.uj.edu.pl>  2009-07-10 07:34:37 PDT ---
s=1414
/home/baryluk/ProjektyZSempa/D/onpd/onp/../onp/utils/misc.d(187): Error:
expression cast(int)(1000 * sqrt2) is not a valid template value argument
/home/baryluk/ProjektyZSempa/D/onpd/onp/../onp/utils/misc.d(187): Error:
expression cast(int)(1000 * sqrt2) is not a valid template value argument
/home/baryluk/ProjektyZSempa/D/onpd/onp/../onp/utils/misc.d(186): Error:
expression cast(int)(1000 * (1 + sqrt2 / 2)) is not a valid template value
argument
...

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--- Comment #2 from Witold Baryluk <baryluk@smp.if.uj.edu.pl>  2009-07-10 07:48:34 PDT ---
Created an attachment (id=420)
 --> (http://d.puremagic.com/issues/attachment.cgi?id=420)
Source code which should compile

Test case

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--- Comment #3 from Witold Baryluk <baryluk@smp.if.uj.edu.pl>  2009-07-10 08:07:07 PDT ---
Simpler example

/** Square root of 2 */
static const double sqrt2 = ctfe_sqrt(2.0);

template X(E ...) { alias E X; }

//alias X!(sqrt2/1.0, sqrt2/2.0) X2; // doesn't work
//alias X!(sqrt2*sqrt2) X3; // doesn't work
static const double sqrt22 = sqrt2*sqrt2;
//alias X!(sqrt22) X4; // doesn't work

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--- Comment #4 from Witold Baryluk <baryluk@smp.if.uj.edu.pl>  2009-07-10 08:15:21 PDT ---
Additionally if i omit "double" in "static const double", it compiles! It is the same type!


I was also testing this ctfe function

T i(T)(T x) {
  return x;
}


and only with T=float,double,real i got errors.

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Don <clugdbug@yahoo.com.au> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch
                 CC|                            |clugdbug@yahoo.com.au
           Platform|Other                       |All
            Summary|can't fully use floats      |can't fully use
                   |computed in CTFE as         |compile-time floats as
                   |template parameters         |template parameters
         OS/Version|Linux                       |All




--- Comment #5 from Don <clugdbug@yahoo.com.au>  2009-07-13 00:09:29 PDT ---
Reduced test case shows it doesn't require CTFE:
-----
enum float one = 1 * 1;
template X(float E) { int X = 2; }
alias X!(one * one) X3;
----

This is really complicated, and took me ages to track down.
First problem is in declaration.c, near the end of VarDeclaration::semantic().
It calculates the value of the manifest constant, but discards the result
unless
it was an int or a string! That's a waste, since it was successfully
calculated.

 In optimize.c expandVar() copys the exprInitializer and semantically analyzes
it, but it doesn't change the exprInitializer. So ei->type remains null the
next time expandVar is called for that same variable.
And since expandVar sets v->scope to NULL, it never gets another chance to
evaluate it.
So in optimize.c line 92, it bypasses the call to e = ei->copy(), returning
NULL from the function.
--> it cannot be evaluated at compile time.

The final patch is tiny: add floating point variables to the list of values which get saved.

// line 1150 declaration.c || e->op==TOKfloat64


            e = e->optimize(WANTvalue | WANTinterpret);
            else
            e = e->optimize(WANTvalue);
-            if (e->op == TOKint64 || e->op == TOKstring)
+            if (e->op == TOKint64 || e->op == TOKstring || e->op==TOKfloat64)
            {
            ei->exp = e;        // no errors, keep result
            }

However, I think the logic in expandVar() is probably also wrong. The bug can also be fixed by adding this line in optimize.c, line 89:

            e = e->semantic(v->scope);
            e = e->implicitCastTo(v->scope, v->type);
+            ei->type = e->type;
            v->scope = NULL;

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |bugzilla@digitalmars.com
         Resolution|                            |FIXED




--- Comment #6 from Walter Bright <bugzilla@digitalmars.com>  2009-09-03 13:40:51 PDT ---
Fixed dmd 2.032

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