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Diffstat (limited to 'openssl/trunk/doc/crypto/OPENSSL_ia32cap.pod')
| -rw-r--r-- | openssl/trunk/doc/crypto/OPENSSL_ia32cap.pod | 35 |
1 files changed, 35 insertions, 0 deletions
diff --git a/openssl/trunk/doc/crypto/OPENSSL_ia32cap.pod b/openssl/trunk/doc/crypto/OPENSSL_ia32cap.pod new file mode 100644 index 00000000..121a8dde --- /dev/null +++ b/openssl/trunk/doc/crypto/OPENSSL_ia32cap.pod @@ -0,0 +1,35 @@ +=pod + +=head1 NAME + +OPENSSL_ia32cap - finding the IA-32 processor capabilities + +=head1 SYNOPSIS + + unsigned long *OPENSSL_ia32cap_loc(void); + #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc())) + +=head1 DESCRIPTION + +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 three bits are +significant, namely bit #28 denoting Hyperthreading, which is used to +distinguish Intel P4 core, bit #26 denoting SSE2 support, and bit #4 +denoting presence of Time-Stamp Counter. Clearing bit #26 at run-time +for example 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. 'env OPENSSL_ia32cap=0x10 apps/openssl', to achieve +same effect without modifying the application source code. +Alternatively you can reconfigure the toolkit with no-sse2 option and +recompile. + +=cut |