https://issues.dlang.org/show_bug.cgi?id=21376

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ibuclaw@gdcproject.org

--- Comment #1 from Iain Buclaw <ibuclaw@gdcproject.org> ---
gdc x86 does not have this problem, so it is the dmd compiler emitting wrong code, not the FPU on i686.

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https://issues.dlang.org/show_bug.cgi?id=21376

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |wrong-code

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https://issues.dlang.org/show_bug.cgi?id=21376

--- Comment #2 from Iain Buclaw <ibuclaw@gdcproject.org> ---
Assembly dump of return statement in `float abs()`

-----------------------------------------------------
dmd x86:
    call   hypotFeeZe
    add    $0x8,%esp
    leave
    ret    $0x8
-----------------------------------------------------
dmd x86_64:
    callq  hypotFeeZe
    add    $0x20,%rsp
    fstpl  -0x20(%rbp)
    movsd  -0x20(%rbp),%xmm0
    cvtsd2ss %xmm0,%xmm0
    leaveq
    retq
-----------------------------------------------------
gdc x86:
    call   hypotFeeZe
    add    $0x18,%esp
    fstps  -0x4(%ebp)
    flds   -0x4(%ebp)
    leave
    ret
-----------------------------------------------------
gdc x86_64:
    callq  hypotFeeZe
    add    $0x20,%rsp
    fstps  -0xc(%rbp)
    movss  -0xc(%rbp),%xmm0
    leaveq
    retq
-----------------------------------------------------

As expected, there is no fstp/fld generated by dmd x86, so the real value returned by hypot is not truncated as per what x86_64 does.

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https://issues.dlang.org/show_bug.cgi?id=21376

--- Comment #3 from Iain Buclaw <ibuclaw@gdcproject.org> ---
hypot() isn't necessary, so that leaves just the lack of fstp/fld after calling
fsqrt.

---
import core.math;

float abs(float re, float im)
{
    float u = fabs(re);
    float v = fabs(im);
    return sqrt(u*u + v*v);
}

void log(real x)
{
    assert(x == 1);
}

void main()
{
    float re = 0.866025403784438646787;
    float im = 0.5;
    return log(abs(re, im));
}

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https://issues.dlang.org/show_bug.cgi?id=21376

--- Comment #4 from Iain Buclaw <ibuclaw@gdcproject.org> ---
(In reply to Iain Buclaw from comment #3)
>     return sqrt(u*u + v*v);

-----------------------------------------------------
dmd x86:
    movss  %xmm0,-0x18(%ebp)
    flds   -0x18(%ebp)
    fmul   %st(0),%st
    movss  %xmm2,-0x18(%ebp)
    flds   -0x18(%ebp)
    fmul   %st(0),%st
    faddp  %st,%st(1)
    fsqrt
    leave
    ret    $0x8
-----------------------------------------------------
dmd x86_64:
    movss  %xmm0,-0x30(%rbp)
    flds   -0x30(%rbp)
    fmul   %st(0),%st
    movss  %xmm2,-0x30(%rbp)
    flds   -0x30(%rbp)
    fmul   %st(0),%st
    faddp  %st,%st(1)
    fsqrt
    fstps  -0x30(%rbp)
    movss  -0x30(%rbp),%xmm0
    leaveq
    retq
-----------------------------------------------------

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https://issues.dlang.org/show_bug.cgi?id=21376

Dlang Bot <dlang-bot@dlang.rocks> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull

--- Comment #5 from Dlang Bot <dlang-bot@dlang.rocks> ---
@ibuclaw updated dlang/dmd pull request #12073 "fix Issue 21515 extern(C) and
extern(C++) returns creal in wrong order" fixing this issue:

- fix Issue 21376 - Returning 32-bit floats have wrong precision on i386

https://github.com/dlang/dmd/pull/12073

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https://issues.dlang.org/show_bug.cgi?id=21376

--- Comment #6 from Iain Buclaw <ibuclaw@gdcproject.org> ---
(In reply to Dlang Bot from comment #5)
> @ibuclaw updated dlang/dmd pull request #12073 "fix Issue 21515 extern(C)
> and extern(C++) returns creal in wrong order" fixing this issue:
> 
> - fix Issue 21376 - Returning 32-bit floats have wrong precision on i386
> 
> https://github.com/dlang/dmd/pull/12073

Ignore this, I attempted fixing, but it's all horribly broken.

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https://issues.dlang.org/show_bug.cgi?id=21376

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |backend

--

https://issues.dlang.org/show_bug.cgi?id=21376

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P1                          |P2

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https://issues.dlang.org/show_bug.cgi?id=21376

Iain Buclaw <ibuclaw@gdcproject.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://issues.dlang.org/sh
                   |                            |ow_bug.cgi?id=21581

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