Richard Salz wrote: > Kyle's claim about things like cache's and registers is wrong, not even > sort-of right. The standard talks about only in terms of > sequence points, > and volatile limits what can be done in terms of sequence points. So > extern volatile char* p; > int i, j; > i = *p; > j = *p; > The standard says that the compiler may not treat this as > j = i = *p; > > *and that's all it says.*
Suppose another thread does this: *p=99; *p=98; Would a compiler that let another code running your code above get 'i' equal to 98 and 'p' equal to 99 be broken in your opinion? I've seen code generated on weakly-ordered memory platforms, and memory barriers are not placed between stores to volatiles. The problem is that it is not well-defined to talk about the order in which operations take place. The order can be different depending upon where you look (one can be first in the instruction stream but last out of the write posting buffer). The standard is discussed in terms of an abstract machine and the machine the code is running on may bear only as much resemblance to the abstract machine as is needed to make strictly-compliant code work. DS ______________________________________________________________________ OpenSSL Project http://www.openssl.org Development Mailing List openssl-dev@openssl.org Automated List Manager [EMAIL PROTECTED]
