2015-03-29 20:15 GMT+02:00 Matt Turner <matts...@gmail.com>:
> On Sun, Mar 29, 2015 at 11:05 AM, Thomas Helland
> <thomashellan...@gmail.com> wrote:
>> Since a pointer is basically just an int we can use integer hashing.
>> This one is taken from https://gist.github.com/badboy/6267743
>> A google search seems to suggest this is a common and good algorithm.
>> Since it operates 32 bits at a time it is really effective.
>> assert that we are hashing 32bit aligned pointers.
>>
>> Signed-off-by: Thomas Helland <thomashellan...@gmail.com>
>> ---
>> src/util/hash_table.c | 24 ++++++++++++++++++++++--
>> 1 file changed, 22 insertions(+), 2 deletions(-)
>>
>> diff --git a/src/util/hash_table.c b/src/util/hash_table.c
>> index 24184c0..54d04ef 100644
>> --- a/src/util/hash_table.c
>> +++ b/src/util/hash_table.c
>> @@ -393,6 +393,15 @@ _mesa_hash_table_random_entry(struct hash_table *ht,
>> return NULL;
>> }
>>
>> +static inline uint32_t
>> +hash_32bit_int(uint32_t a) {
>> + a = (a ^ 61) ^ (a >> 16);
>> + a = a + (a << 3);
>> + a = a ^ (a >> 4);
>> + a = a * 0x27d4eb2d;
>> + a = a ^ (a >> 15);
>> + return a;
>> +}
>>
>> /**
>> * Quick FNV-1a hash implementation based on:
>> @@ -406,8 +415,19 @@ _mesa_hash_table_random_entry(struct hash_table *ht,
>> uint32_t
>> _mesa_hash_data(const void *data, size_t size)
>> {
>> - return _mesa_fnv32_1a_accumulate_block(_mesa_fnv32_1a_offset_bias,
>> - data, size);
>> + uint32_t hash = _mesa_fnv32_1a_offset_bias;
>> + const uint32_t *ints = (const uint32_t *) data;
>> +
>> + assert((size % 4) == 0);
>
> Not sure if we can mix code and declarations. This might need to go
> after the declaration of i.
>
Darn. Rebase failure on my part.
Will post a V2 ASAP.
>> +
>> + uint32_t i = size / 4;
>> +
>> + while (i-- != 0) {
>> + hash ^= hash_32bit_int(*ints);
>> + ints++;
>> + }
>
> This would read a lot better as
>
> for (i = size / 4; i != 0; i--) {
> hash ^= hash_32_bit_int(ints[i]);
> }
I'll get this into the V2 as well.
Thanks for the fast response =)
>
>> +
>> + return hash;
>> }
>>
>> /** FNV-1a string hash implementation */
>> --
>> 2.3.4
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