Can _mm_crc32_u64() return a value that is bigger than MAX_UINT32?

[Alex Lyakas]

Hi Segher,

Thanks for your response.

Can you confirm then, that despite returning a 64-bit value, the result will 
never actually cross the maximal 32-bit value? Can you perhaps point us at 
gcc code, so that we can try to ensure that?

Thanks,
Alex.


-----Original Message----- 
From: Segher Boessenkool
Sent: Monday, February 12, 2018 5:01 PM
To: Eitan Azriel
Cc: gcc-help@gcc.gnu.org ; Alex Lyakas ; hjl.tools@gmail.com
Subject: Re: Can _mm_crc32_u64() return a value that is bigger than 
MAX_UINT32?

Hello,

On Mon, Feb 12, 2018 at 03:24:14PM +0200, Eitan Azriel wrote:
> The signature of _mm_crc32_u64() is:
> unsigned int64 _mm_crc32_u64 (
>    unsigned __int64 crc,
>    unsigned __int64 v
> );
>
> Why does it return int64, and not uint32? Shouldn't it return a valid 
> CRC32
> value?

GCC uses int64 because that is what the ABI/API says it should do.

Presumably it uses int64 for output because it does use it for input
and there was the desire to use the same type everywhere.


Segher