Merge branch 'vendor/OPENSSL'
[dragonfly.git] / secure / lib / libcrypto / man / OPENSSL_ia32cap.3
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131.IX Title "OPENSSL_ia32cap 3"
18ed9402 132.TH OPENSSL_ia32cap 3 "2008-09-27" "0.9.8i" "OpenSSL"
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133.SH "NAME"
134OPENSSL_ia32cap \- finding the IA\-32 processor capabilities
135.SH "SYNOPSIS"
136.IX Header "SYNOPSIS"
137.Vb 2
138\& unsigned long *OPENSSL_ia32cap_loc(void);
139\& #define OPENSSL_ia32cap (*(OPENSSL_ia32cap_loc()))
140.Ve
141.SH "DESCRIPTION"
142.IX Header "DESCRIPTION"
143Value returned by \fIOPENSSL_ia32cap_loc()\fR is address of a variable
144containing \s-1IA\-32\s0 processor capabilities bit vector as it appears in \s-1EDX\s0
145register after executing \s-1CPUID\s0 instruction with EAX=1 input value (see
146Intel Application Note #241618). Naturally it's meaningful on IA\-32[E]
147platforms only. The variable is normally set up automatically upon
148toolkit initialization, but can be manipulated afterwards to modify
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149crypto library behaviour. For the moment of this writing six bits are
150significant, namely:
151.PP
1521. bit #28 denoting Hyperthreading, which is used to distiguish
153 cores with shared cache;
1542. bit #26 denoting \s-1SSE2\s0 support;
1553. bit #25 denoting \s-1SSE\s0 support;
1564. bit #23 denoting \s-1MMX\s0 support;
1575. bit #20, reserved by Intel, is used to choose between \s-1RC4\s0 code
158 pathes;
1596. bit #4 denoting presence of Time-Stamp Counter.
160.PP
161For example, clearing bit #26 at run-time disables high-performance
162\&\s-1SSE2\s0 code present in the crypto library. You might have to do this if
163target OpenSSL application is executed on \s-1SSE2\s0 capable \s-1CPU\s0, but under
164control of \s-1OS\s0 which does not support \s-1SSE2\s0 extentions. Even though you
165can manipulate the value programmatically, you most likely will find it
166more appropriate to set up an environment variable with the same name
167prior starting target application, e.g. on Intel P4 processor 'env
168OPENSSL_ia32cap=0x12900010 apps/openssl', to achieve same effect
169without modifying the application source code. Alternatively you can
170reconfigure the toolkit with no\-sse2 option and recompile.