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.\" ========================================================================
.\"
.IX Title "OPENSSL_ia32cap 3"
.TH OPENSSL_ia32cap 3 "2007-10-24" "0.9.8g" "OpenSSL"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
OPENSSL_ia32cap \- finding the IA\-32 processor capabilities
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\& unsigned long *OPENSSL_ia32cap_loc(void);
\& #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc()))
.Ve
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
Value returned by \fIOPENSSL_ia32cap_loc()\fR is address of a variable
containing \s-1IA\-32\s0 processor capabilities bit vector as it appears in \s-1EDX\s0
register after executing \s-1CPUID\s0 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 \s-1SSE2\s0 support, and bit #4
denoting presence of Time-Stamp Counter. Clearing bit #26 at run-time
for example disables high-performance \s-1SSE2\s0 code present in the crypto
library. You might have to do this if target OpenSSL application is
executed on \s-1SSE2\s0 capable \s-1CPU\s0, but under control of \s-1OS\s0 which does not
support \s-1SSE2\s0 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.