Manual Pages for UNIX Operating System command usage for man OPENSSL_ia32cap

OpenSSL                                 OPENSSL_ia32cap(3openssl)



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     OPENSSL_ia32cap - finding the IA-32 processor capabilities

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      unsigned long *OPENSSL_ia32cap_loc(void);
      #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc()))


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     Value returned by OPENSSL_ia32cap_loc() is address of a
     variable containing IA-32 processor capabilities bit vector
     as it appears in EDX register after executing CPUID
     instruction with EAX=1 input value (see Intel Application
     Note #241618). Naturally it's meaningful on IA-32[E]
     platforms only. The variable is normally set up
     automatically upon toolkit initialization, but can be
     manipulated afterwards to modify crypto library behaviour.
     For the moment of this writing six bits are significant,
     namely:

     1. bit #28 denoting Hyperthreading, which is used to
     distiguish
        cores with shared cache; 2. bit #26 denoting SSE2
     support; 3. bit #25 denoting SSE support; 4. bit #23
     denoting MMX support; 5. bit #20, reserved by Intel, is used
     to choose between RC4 code
        pathes; 6. bit #4 denoting presence of Time-Stamp
     Counter.

     For example, clearing bit #26 at run-time disables high-
     performance SSE2 code present in the crypto library. You
     might have to do this if target OpenSSL application is
     executed on SSE2 capable CPU, but under control of OS which
     does not support SSE2 extentions. Even though you can
     manipulate the value programmatically, you most likely will
     find it more appropriate to set up an environment variable
     with the same name prior starting target application, e.g.
     on Intel P4 processor 'env OPENSSL_ia32cap=0x12900010
     apps/openssl', to achieve same effect without modifying the
     application source code. Alternatively you can reconfigure
     the toolkit with no-sse2 option and recompile.














11/Nov/2007            Last change: 0.9.8o                      1