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Re: [Qemu-devel] [PATCH 1/4] net: move CRC32 calculation from compute_mc
From: |
Mark Cave-Ayland |
Subject: |
Re: [Qemu-devel] [PATCH 1/4] net: move CRC32 calculation from compute_mcast_idx() into its own net_crc32() function |
Date: |
Fri, 18 Aug 2017 19:11:33 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 18/08/17 18:06, Philippe Mathieu-Daudé wrote:
> On 08/18/2017 01:51 PM, Philippe Mathieu-Daudé wrote:
>> On 08/18/2017 11:15 AM, Mark Cave-Ayland wrote:
>>> Separate out the standard ethernet CRC32 calculation into a new
>>> net_crc32()
>>> function, renaming the constant POLYNOMIAL to POLYNOMIAL_BE to make
>>> it clear
>>> that this is a big-endian CRC32 calculation.
>>>
>>> Then remove the existing implementation from compute_mcast_idx() and
>>> call the
>>> new function in its place.
>>>
>>> Signed-off-by: Mark Cave-Ayland <address@hidden>
>>> ---
>>> include/net/net.h | 3 ++-
>>> net/net.c | 16 +++++++++++-----
>>> 2 files changed, 13 insertions(+), 6 deletions(-)
>>>
>>> diff --git a/include/net/net.h b/include/net/net.h
>>> index 1c55a93..586098c 100644
>>> --- a/include/net/net.h
>>> +++ b/include/net/net.h
>>> @@ -227,7 +227,8 @@ NetClientState *net_hub_port_find(int hub_id);
>>> void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
>>> -#define POLYNOMIAL 0x04c11db6
>>> +#define POLYNOMIAL_BE 0x04c11db6
>>> +uint32_t net_crc32(const uint8_t *p, int len);
>>> unsigned compute_mcast_idx(const uint8_t *ep);
>>> #define vmstate_offset_macaddr(_state, _field) \
>>> diff --git a/net/net.c b/net/net.c
>>> index 0e28099..a856907 100644
>>> --- a/net/net.c
>>> +++ b/net/net.c
>>> @@ -1568,25 +1568,31 @@ int net_client_parse(QemuOptsList *opts_list,
>>> const char *optarg)
>>> /* From FreeBSD */
>>> /* XXX: optimize */
>>> -unsigned compute_mcast_idx(const uint8_t *ep)
>>> +uint32_t net_crc32(const uint8_t *p, int len)
>>
>> imho there is no point in using signed length.
>>
>>> {
>>> uint32_t crc;
>>> int carry, i, j;
>>> uint8_t b;
>>> crc = 0xffffffff;
>>> - for (i = 0; i < 6; i++) {
>>> - b = *ep++;
>>> + for (i = 0; i < len; i++) {
>>> + b = *p++;
>>> for (j = 0; j < 8; j++) {
>>> carry = ((crc & 0x80000000L) ? 1 : 0) ^ (b & 0x01);
>>> crc <<= 1;
>>> b >>= 1;
>>> if (carry) {
>>> - crc = ((crc ^ POLYNOMIAL) | carry);
>>> + crc = ((crc ^ POLYNOMIAL_BE) | carry);
>>> }
>>> }
>>> }
>>> - return crc >> 26;
>>> +
>>> + return crc;
>>> +}
>>> +
>>> +unsigned compute_mcast_idx(const uint8_t *ep)
>>> +{
>>> + return net_crc32(ep, 6) >> 26;
>>
>> while here let's use ETH_ALEN
>>
>
> reading the next patches, what do you think about:
>
> static inline uint32_t mac_crc32_be(const uint8_t *p)
> {
> return net_crc32_be(ep, ETH_ALEN);
> }
>
> unsigned compute_mcast_idx(const uint8_t *ep)
> {
> return mac_crc32_be(p) >> 26;
> }
Yes, using ETH_ALEN looks like a good idea - I can do that for the next
revision.
As for the naming of the functions, I've followed the kernel convention
that by default the CRC32 functions are big-endian unless they have a
_le suffix. I don't really feel strongly either way, so I'm happy to go
with whatever naming scheme Jason prefers.
ATB,
Mark.