> > > __asm rdtsc
> > > __asm sub eax, time_low // Find the difference
> > > __asm sub edx, time_high
> > >
> > > __asm div mhz // Unsigned divide EDX:EAX by mhz
> > >
> > > __asm mov time, eax
> > > printf("Seconds: %u\n", time);
> > >
> > > What exactly does the div line do?
> >
> > divides the number of cycles measured by the number of hertz which
> > leads to the seconds consumed ,-)
> >
>
> I know that's what it does,
> but what is the dividend? Is it the 64-bit number created by combining eax
> and edx? I don't understand where the dividend on that line is coming from.
> And if it is a 64-bit number, how do I change the mull assembly in
> do_fast_getttimeoffset to do the same thing?
>
From the Intel Instruction Set Reference Manual, page 219:
(http://developer.intel.com/design/pentium4/manuals/245471.htm)
Operand Size Dividend Divisor Quotient Remainder Maximum Quotient
Word/byte AX r/m8 AL AH 255
Doubleword/word DX:AX r/m16 AX DX 65,535
Quadword/doubleword EDX:EAX r/m32 EAX EDX 232 1
- If you read the rdtsc, the counters are stored in EDX:EAX.
- If you read the lines I posted, the dividend is stored in EDX:EAX
- If you read further these lines, the divisor may be a register or a
memory location with size of 32bit.
- If you have any further questions, please ask.
--lpr
--
Lukas Ruf
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