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Re: [PATCH][AArch64] vrnd<*>_f64 patch for stage-1
- From: Richard Henderson <rth at redhat dot com>
- To: Alex Velenko <Alex dot Velenko at arm dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Cc: Marcus Shawcroft <Marcus dot Shawcroft at arm dot com>
- Date: Thu, 13 Feb 2014 09:43:06 -0800
- Subject: Re: [PATCH][AArch64] vrnd<*>_f64 patch for stage-1
- Authentication-results: sourceware.org; auth=none
- References: <52FCA9CB dot 2010201 at arm dot com>
On 02/13/2014 03:17 AM, Alex Velenko wrote:
> +/* Sets "rmode" field of "FPCR" control register to
> + "FPROUNDING_ZERO". */
Comment is wrong, or at least misleading.
> +void __inline __attribute__ ((__always_inline__))
> +set_rounding_mode (uint32_t mode)
> +{
> + uint32_t r;
> +
> + /* Read current FPCR. */
> + asm volatile ("mrs %[r], fpcr" : [r] "=r" (r) : :);
> +
> + /* Clear rmode. */
> + r &= 3 << RMODE_START;
~(3 << RMODE_START)
> + /* Calculate desired FPCR. */
> + r |= mode << RMODE_START;
> +
> + /* Write desired FPCR back. */
> + asm volatile ("msr fpcr, %[r]" : : [r] "r" (r) :);
> +}
Fortunately for this testcase, you do always use FPROUNDING_ZERO == 3 when
calling this function, so the bugs are hidden.
r~