This is the mail archive of the
libc-alpha@sourceware.org
mailing list for the glibc project.
Re: [PATCH] powerpc: New feature - HWCAP/HWCAP2 bits in the TCB
- From: Kalle Olavi Niemitalo <kon at iki dot fi>
- To: libc-alpha <libc-alpha at sourceware dot org>
- Date: Fri, 10 Jul 2015 01:12:46 +0300
- Subject: Re: [PATCH] powerpc: New feature - HWCAP/HWCAP2 bits in the TCB
- Authentication-results: sourceware.org; auth=none
- References: <55760314 dot 6070601 at linux dot vnet dot ibm dot com> <559617FF dot 8010100 at redhat dot com> <20150703085542 dot GE32307 at domone> <55968AF8 dot 8060104 at redhat dot com> <20150703171121 dot GA23898 at domone> <1436283324 dot 12188 dot 25 dot camel at oc7878010663>
Steven Munroe <munroesj@linux.vnet.ibm.comcom> writes:
> if (__builtin_cpu_supports(ARCH_2_07) &&
> __builtin_cpu_supports(VEC_CRYPTO))
>
> This is 3 instructions (lwz, andi., bc) as packed bits, but 5 or 6 as
> byte Boolean.
I would understand 3 instructions for "||" (test the zero flag) but
how do you do it for "&&"? I have hardly any powerpc experience
though, so perhaps there is some trick I don't realize.
If not, and if "&&" is more common than "||" in HWCAP tests, then
would it be worthwhile to invert the HWCAP bits in TCB? I guess
it wouldn't, because such a format would increase the risk that
the program crashes if the bits were not properly initialized
before they were read.