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Re: 64-bit detection

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"James Harris" <james.harris.1@gmail.com> wrote in message 
news:mnns78$v0t$1@dont-email.me...
>
> I didn't know either but found that there is a CPUID bit for it.
>
>  CPUID[0x8000_0001].EDX[29]
>
> Almost by chance I found the following snippet in an AMD manual 
> (24593-Rev. 3.23-May 2013).
>

For future reference and for those who might be looking for the
same answer, here is my code to check for a 64-bit machine.

// Use CPUID to determine if the processor supports long mode:
// reference:
//  - AMD manual (24593-Rev. 3.25-June 2015)
//    http://support.amd.com/TechDocs/24593.pdf
//  - Intel manual Vol 3C, page 34-6, section 34.4.1.1
//           (325384-055US, June 2015)
//    "Support for Intel 64 architecture is reported by:
//           CPUID.80000001:EDX[29] = 1"
//  - Intel manual Vol 2A, page 3-186, Table 3-17
//           (253666-055US, June 2015)
_naked bool is_64bit_cpu() {
  _asm (
    "  mov  eax,80000000h       ; Get highest extended function\n"
    "  cpuid                    ; \n"
    "  cmp  eax,80000001h       ; is at least 80000001h allowed?\n"
    "  jb   short @f            ; If not, long mode not support\n"
    "  mov  eax,80000001h       ; Get extended function 8000001h flags\n"
    "  cpuid                    ; EDX = extended-features flags\n"
    "  bt   edx,29              ; If bit 29 is set, long mode is 
supported\n"
    "  jnc  short @f            ; \n"
    "  mov  eax,1               ; return TRUE\n"
    "  ret                      ; we're done\n"
    "@@:                        ; \n"
    "  xor  eax,eax             ; return FALSE\n"
    "  ret                      ; we're done\n"
  );
}

Notes:
 - I use Alex's SmallerC to compile this to .asm
     https://github.com/alexfru/SmallerC
 - Then I use my NBASM to assemble to binary
     http://www.fysnet.net/newbasic.htm
 - The _naked keyword tells SmallerC not to include
    the epilog and prolog (an addition I made to SmallerC)

Thanks guys for your comments.

Ben

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64-bit detection "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-07-09 16:47 -0700
  Re: 64-bit detection "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-09 23:41 -0400
    Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-10 08:30 +0100
      Re: 64-bit detection "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-10 05:17 -0400
        Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-10 13:41 +0100
          Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-12 19:04 +0100
            Re: 64-bit detection "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-13 02:30 -0400
              Re: 64-bit detection "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-13 02:07 -0700
                Re: 64-bit detection "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-13 23:10 -0400
                Re: 64-bit detection "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-14 01:23 -0700
              Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-13 12:34 +0100
                Re: 64-bit detection "Rod Pemberton" <boo@fasdfrewar.cdm> - 2015-07-13 22:50 -0400
                Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-14 08:37 +0100
                Re: 64-bit detection "Alexei A. Frounze" <alexfrunews@gmail.com> - 2015-07-14 01:41 -0700
                Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-14 10:04 +0100
      Re: 64-bit detection "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-07-10 08:44 -0700
      Re: 64-bit detection "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-07-10 10:52 -0700
    Re: 64-bit detection "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-07-10 08:38 -0700
      Re: 64-bit detection "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-07-10 10:58 -0700
  Re: 64-bit detection CN <qmbmnp3799@pacbell.net> - 2015-07-09 23:00 -0700
    Re: 64-bit detection "Benjamin David Lunt" <zfysz@fysnet.net> - 2015-07-10 08:40 -0700
      Re: 64-bit detection "James Harris" <james.harris.1@gmail.com> - 2015-07-10 21:29 +0100

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