On Mar 19, 9:02 am, Terje Mathisen <spamt...@[EMAIL PROTECTED]
> wrote:
> Tim Roberts wrote:
> > I admit that I lost track part way through, but it looks to me like
you
> > aren't cleaning up thefloatingpointstack when you are done. If you
> > leave stuff on the stack, sooner or later the stack will overflow
(there
> > are only 8 entries, after all), which triggersfloatingpointexceptions.
>
> The easy way to check this is to call your my_pow() function in a loop,
> preferably while inside the debugger, and watch the x87 stack contents.
>
Thanks for replying.
So I try to follow the stack state after each call to my_pow, it
looks ok for a few calls (9), then I see a weird thing: when "fld1" is
executed at some point, it loads a "nan" instead of "1" into st0:
(gdb) ni
0x08048397 270
8: $st7 = 15
7: $st6 = 14
6: $st5 = 13
5: $st4 = 12
4: $st3 = 2
3: $st2 = 0
2: $st1 = 2
1: $st0 = 0
(gdb) ni
0x08048399 270
8: $st7 = 14
7: $st6 = 13
6: $st5 = 12
5: $st4 = 2
4: $st3 = 0
3: $st2 = 2
2: $st1 = 0
1: $st0 = -nan(0xc000000000000000)
So what am I missing here? I have attached the disassembled code at
the end for my_pow.
Thanks,
-Bin
my_pow:
804838a: dd 44 24 04 fldl 0x4(%esp)
804838e: dd 44 24 0c fldl 0xc(%esp)
8048392: d9 e4 ftst
8048394: 9b df e0 fstsw %ax
8048397: d9 e8 fld1
8048399: 9e sahf
804839a: 74 3f je 80483db <my_pow+0x51>
804839c: d8 d9 fcomp %st(1)
804839e: 9b df e0 fstsw %ax
80483a1: d9 c9 fxch %st(1)
80483a3: 9e sahf
80483a4: 74 35 je 80483db <my_pow+0x51>
80483a6: d9 e4 ftst
80483a8: 9b df e0 fstsw %ax
80483ab: 9e sahf
80483ac: 74 2d je 80483db <my_pow+0x51>
80483ae: 73 2c jae 80483dc <my_pow+0x52>
80483b0: d9 c9 fxch %st(1)
80483b2: d9 c0 fld %st(0)
80483b4: d9 fc frndint
80483b6: d8 d9 fcomp %st(1)
80483b8: 9b df e0 fstsw %ax
80483bb: d9 c9 fxch %st(1)
80483bd: 9e sahf
80483be: 75 1c jne 80483dc <my_pow+0x52>
80483c0: d9 e8 fld1
80483c2: d8 c0 fadd %st(0),%st
80483c4: d8 fa fdivr %st(2),%st
80483c6: d9 fc frndint
80483c8: d8 c0 fadd %st(0),%st
80483ca: d8 da fcomp %st(2)
80483cc: 9b df e0 fstsw %ax
80483cf: d9 e0 fchs
80483d1: 9e sahf
80483d2: 74 08 je 80483dc <my_pow+0x52>
80483d4: e8 03 00 00 00 call 80483dc <my_pow+0x52>
80483d9: d9 e0 fchs
80483db: c3 ret
80483dc: d9 f1 fyl2x
80483de: e9 96 ff ff ff jmp 8048379 <__finexp>
08048379 <__finexp>:
8048379: dd d1 fst %st(1)
804837b: d9 fc frndint
804837d: dd d2 fst %st(2)
804837f: de e9 fsubrp %st,%st(1)
8048381: d9 f0 f2xm1
8048383: d9 e8 fld1
8048385: de c1 faddp %st,%st(1)
8048387: d9 fd fscale
8048389: c3 ret
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