X-Git-Url: https://git.openssl.org/gitweb/?p=openssl.git;a=blobdiff_plain;f=doc%2Fcrypto%2FOPENSSL_ia32cap.pod;h=2e659d34a5c43b29e36b2e622a30fd165c99aa1f;hp=03ac6e6834bd672dad99eadb583ee9099e13fb07;hb=162f677def843739f4984d674b4ad33eb726e7ea;hpb=287546242539e686ef1233d0a7c57c935fb61c3f;ds=sidebyside

diff --git a/doc/crypto/OPENSSL_ia32cap.pod b/doc/crypto/OPENSSL_ia32cap.pod
index 03ac6e6834..2e659d34a5 100644
--- a/doc/crypto/OPENSSL_ia32cap.pod
+++ b/doc/crypto/OPENSSL_ia32cap.pod
@@ -17,20 +17,27 @@ 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 five bits are
-significant, namely bit #28 denoting Hyperthreading, which is used to
-distinguish Intel P4 core, bit #26 denoting SSE2 support, bit #25
-denoting SSE support, bit #23 denoting MMX 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=0x12800010 apps/openssl', to
-achieve same effect without modifying the application source code.
-Alternatively you can reconfigure the toolkit with no-sse2 option and
-recompile.
+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.
 
 =cut