Update files for OpenSSL-1.0.0f import.
[dragonfly.git] / secure / lib / libcrypto / man / OPENSSL_ia32cap.3
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126.IX Title "OPENSSL_ia32cap 3"
e3261593 127.TH OPENSSL_ia32cap 3 "2012-01-04" "1.0.0f" "OpenSSL"
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132.SH "NAME"
133OPENSSL_ia32cap \- finding the IA\-32 processor capabilities
134.SH "SYNOPSIS"
135.IX Header "SYNOPSIS"
136.Vb 2
137\& unsigned long *OPENSSL_ia32cap_loc(void);
138\& #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc()))
139.Ve
140.SH "DESCRIPTION"
141.IX Header "DESCRIPTION"
142Value returned by \fIOPENSSL_ia32cap_loc()\fR is address of a variable
143containing \s-1IA\-32\s0 processor capabilities bit vector as it appears in \s-1EDX\s0
144register after executing \s-1CPUID\s0 instruction with EAX=1 input value (see
145Intel Application Note #241618). Naturally it's meaningful on IA\-32[E]
146platforms only. The variable is normally set up automatically upon
147toolkit initialization, but can be manipulated afterwards to modify
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148crypto library behaviour. For the moment of this writing six bits are
149significant, namely:
150.PP
1511. bit #28 denoting Hyperthreading, which is used to distiguish
152 cores with shared cache;
1532. bit #26 denoting \s-1SSE2\s0 support;
1543. bit #25 denoting \s-1SSE\s0 support;
1554. bit #23 denoting \s-1MMX\s0 support;
1565. bit #20, reserved by Intel, is used to choose between \s-1RC4\s0 code
157 pathes;
1586. bit #4 denoting presence of Time-Stamp Counter.
159.PP
160For example, clearing bit #26 at run-time disables high-performance
161\&\s-1SSE2\s0 code present in the crypto library. You might have to do this if
162target OpenSSL application is executed on \s-1SSE2\s0 capable \s-1CPU\s0, but under
163control of \s-1OS\s0 which does not support \s-1SSE2\s0 extentions. Even though you
164can manipulate the value programmatically, you most likely will find it
165more appropriate to set up an environment variable with the same name
166prior starting target application, e.g. on Intel P4 processor 'env
167OPENSSL_ia32cap=0x12900010 apps/openssl', to achieve same effect
168without modifying the application source code. Alternatively you can
169reconfigure the toolkit with no\-sse2 option and recompile.