Any float point calculation in both main Fiber/slave Fiber will cause uncertain result, unless your CPU is 386sx with FP emu clib.

This bug exsits on both Win32 and x86 Linux Tango lib. Please dont use Fiber class unless you are sure there no any float point calculation in you program and in ALL api/lib you imported.

Thread.d firber context switch bug, there is no FP register save/restore. EBX ESI EDI EBP ESP IP FS only. this code is unsafe!

==========CUT from tango/core/Thread.d line:2369-2405=======
        version( AsmX86_Win32 )
        {
            asm
            {
                naked;

                // save current stack state
                push EBP;
                mov  EBP, ESP;
                push EAX;
                push dword ptr FS:[0];
                push dword ptr FS:[4];
                push dword ptr FS:[8];
                push EBX;
                push ESI;
                push EDI;

                // store oldp again with more accurate address
                mov EAX, dword ptr 8[EBP];
                mov [EAX], ESP;
                // load newp to begin context switch
                mov ESP, dword ptr 12[EBP];

                // load saved state from new stack
                pop EDI;
                pop ESI;
                pop EBX;
                pop dword ptr FS:[8];
                pop dword ptr FS:[4];
                pop dword ptr FS:[0];
                pop EAX;
                pop EBP;

                // 'return' to complete switch
                ret;
            }
        }
===============CUT END====================


GNU glibc2.7 swapcontext.S code is safe
===============CUT===================
ENTRY(__swapcontext)
 /* Load address of the context data structure we save in.  */
 movl 4(%esp), %eax

 /* Return value of swapcontext.  EAX is the only register whose
    value is not preserved.  */
 movl $0, oEAX(%eax)

 /* Save the 32-bit register values and the return address.  */
 movl %ecx, oECX(%eax)
 movl %edx, oEDX(%eax)
 movl %edi, oEDI(%eax)
 movl %esi, oESI(%eax)
 movl %ebp, oEBP(%eax)
 movl (%esp), %ecx
 movl %ecx, oEIP(%eax)
 leal 4(%esp), %ecx
 movl %ecx, oESP(%eax)
 movl %ebx, oEBX(%eax)

 /* Save the FS segment register.  */
 xorl %edx, %edx
 movw %fs, %dx
 movl %edx, oFS(%eax)

 /* We have separate floating-point register content memory on the
    stack.  We use the __fpregs_mem block in the context.  Set the
    links up correctly.  */
 leal oFPREGSMEM(%eax), %ecx
 movl %ecx, oFPREGS(%eax)
 /* Save the floating-point context.  */
 fnstenv (%ecx)

 /* Load address of the context data structure we have to load.  */
 movl 8(%esp), %ecx

 /* Save the current signal mask and install the new one.  */
 pushl %ebx
 leal oSIGMASK(%eax), %edx
 leal oSIGMASK(%ecx), %ecx
 movl $SIG_SETMASK, %ebx
 movl $__NR_sigprocmask, %eax
 ENTER_KERNEL
 popl %ebx
 cmpl $-4095, %eax  /* Check %eax for error.  */
 jae SYSCALL_ERROR_LABEL /* Jump to error handler if error.  */

 /* EAX was modified, reload it.  */
 movl 8(%esp), %eax

 /* Restore the floating-point context.  Not the registers, only the
    rest.  */
 movl oFPREGS(%eax), %ecx
 fldenv (%ecx)

 /* Restore the FS segment register.  We don't touch the GS register
    since it is used for threads.  */
 movl oFS(%eax), %edx
 movw %dx, %fs

 /* Fetch the address to return to.  */
 movl oEIP(%eax), %ecx

 /* Load the new stack pointer.  */
 movl oESP(%eax), %esp

 /* Push the return address on the new stack so we can return there.  */
 pushl %ecx

 /* Load the values of all the 32-bit registers (except ESP).
    Since we are loading from EAX, it must be last.  */
 movl oEDI(%eax), %edi
 movl oESI(%eax), %esi
 movl oEBP(%eax), %ebp
 movl oEBX(%eax), %ebx
 movl oEDX(%eax), %edx
 movl oECX(%eax), %ecx
 movl oEAX(%eax), %eax

 /* The following 'ret' will pop the address of the code and jump
    to it.  */

L(pseudo_end):
 ret
PSEUDO_END(__swapcontext)
=============CUT END=================


Microsoft Windows Server 2003 code also safe
===========Kernel32.dll SwitchToFiber==============
7C821804 k>/$  64:8B15 18000000  mov edx,dword ptr fs:[18]
7C82180B   |.  8B42 10           mov eax,dword ptr ds:[edx+10]
7C82180E   |.  8998 B8000000     mov dword ptr ds:[eax+B8],ebx
7C821814   |.  89B8 B0000000     mov dword ptr ds:[eax+B0],edi
7C82181A   |.  89B0 B4000000     mov dword ptr ds:[eax+B4],esi
7C821820   |.  89A8 C8000000     mov dword ptr ds:[eax+C8],ebp
7C821826   |.  8178 14 0F000100  cmp dword ptr ds:[eax+14],1000F
7C82182D   |.  75 14             jnz short kernel32.7C821843
7C82182F   |.  9B                wait
7C821830   |.  DD78 34           fstsw word ptr ds:[eax+34]
7C821833   |.  D978 30           fstcw word ptr ds:[eax+30]
7C821836   |.  803D 7A02FE7F 01  cmp byte ptr ds:[7FFE027A],1
7C82183D   |.  75 04             jnz short kernel32.7C821843
7C82183F   |.  0FAE58 28         stmxcsr dword ptr ds:[eax+28]
7C821843   |>  89A0 D8000000     mov dword ptr ds:[eax+D8],esp
7C821849   |.  8B8A B40F0000     mov ecx,dword ptr ds:[edx+FB4]
7C82184F   |.  8988 E8020000     mov dword ptr ds:[eax+2E8],ecx
7C821855   |.  8B8A A8010000     mov ecx,dword ptr ds:[edx+1A8]
7C82185B   |.  8988 E4020000     mov dword ptr ds:[eax+2E4],ecx
7C821861   |.  8B0A              mov ecx,dword ptr ds:[edx]
7C821863   |.  8B5A 08           mov ebx,dword ptr ds:[edx+8]
7C821866   |.  8BB2 780F0000     mov esi,dword ptr ds:[edx+F78]
7C82186C   |.  8948 04           mov dword ptr ds:[eax+4],ecx
7C82186F   |.  8958 0C           mov dword ptr ds:[eax+C],ebx
7C821872   |.  89B0 EC020000     mov dword ptr ds:[eax+2EC],esi
7C821878   |.  8B4C24 04         mov ecx,dword ptr ss:[esp+4]
7C82187C   |.  894A 10           mov dword ptr ds:[edx+10],ecx
7C82187F   |.  8B71 04           mov esi,dword ptr ds:[ecx+4]
7C821882   |.  8B59 08           mov ebx,dword ptr ds:[ecx+8]
7C821885   |.  8932              mov dword ptr ds:[edx],esi
7C821887   |.  895A 04           mov dword ptr ds:[edx+4],ebx
7C82188A   |.  8B71 0C           mov esi,dword ptr ds:[ecx+C]
7C82188D   |.  8B59 10           mov ebx,dword ptr ds:[ecx+10]
7C821890   |.  8BB9 EC020000     mov edi,dword ptr ds:[ecx+2EC]
7C821896   |.  8972 08           mov dword ptr ds:[edx+8],esi
7C821899   |.  899A 0C0E0000     mov dword ptr ds:[edx+E0C],ebx
7C82189F   |.  89BA 780F0000     mov dword ptr ds:[edx+F78],edi
7C8218A5   |.  8BB1 E4020000     mov esi,dword ptr ds:[ecx+2E4]
7C8218AB   |.  89B2 A8010000     mov dword ptr ds:[edx+1A8],esi
7C8218B1   |.  8179 14 0F000100  cmp dword ptr ds:[ecx+14],1000F
7C8218B8   |.  75 28             jnz short kernel32.7C8218E2
7C8218BA   |.  8B58 34           mov ebx,dword ptr ds:[eax+34]
7C8218BD   |.  66:3B59 34        cmp bx,word ptr ds:[ecx+34]
7C8218C1   |.  75 09             jnz short kernel32.7C8218CC
7C8218C3   |.  8B58 30           mov ebx,dword ptr ds:[eax+30]
7C8218C6   |.  66:3B59 30        cmp bx,word ptr ds:[ecx+30]
7C8218CA   |.  74 09             je short kernel32.7C8218D5
7C8218CC   |>  66:C741 38 FFFF   mov word ptr ds:[ecx+38],0FFFF
7C8218D2   |.  D961 30           fldenv (28-byte) ptr ds:[ecx+30]
7C8218D5   |>  803D 7A02FE7F 01  cmp byte ptr ds:[7FFE027A],1
7C8218DC   |.  75 04             jnz short kernel32.7C8218E2
7C8218DE   |.  0FAE51 28         ldmxcsr dword ptr ds:[ecx+28]
7C8218E2   |>  8BB9 B0000000     mov edi,dword ptr ds:[ecx+B0]
7C8218E8   |.  8BB1 B4000000     mov esi,dword ptr ds:[ecx+B4]
7C8218EE   |.  8BA9 C8000000     mov ebp,dword ptr ds:[ecx+C8]
7C8218F4   |.  8B99 B8000000     mov ebx,dword ptr ds:[ecx+B8]
7C8218FA   |.  8B81 E8020000     mov eax,dword ptr ds:[ecx+2E8]
7C821900   |.  8982 B40F0000     mov dword ptr ds:[edx+FB4],eax
7C821906   |.  8BA1 D8000000     mov esp,dword ptr ds:[ecx+D8]
7C82190C   \.  C2 0400           retn 4
===============CUT END=====================