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Remove the siphash->hmac-md5 switch after 36 bytes.

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Currently, siphash is used for strings up to 36 bytes. hmac-md5 is used
for longer strings.

This switch-over is a remnant of the previous hash-function that was
used, which apparently was slower with longer input strings.

This change serves no purpose anymore. I performed a few performance tests
on strings of varying sizes:

For a 40 byte string with 10 million iterations:

siphash: 0.31 seconds
hmac-md5: 3.8 seconds

For a 1080 byte string with 10 million iterations:

siphash: 4.2 seconds
hmac-md5: 17 seconds

For a 18360 byte string with 10 million iterations:

siphash: 69 seconds
hmac-md5: 240 seconds

Hence, this commit removes the use of hmac-md5.

This change causes reordering of lines in a few logs.

This commit also changes the datastructure for the seed in probabilistic/Hasher
to get rid of a type-punning warning.
This commit is contained in:
Johanna Amann 2020-04-24 13:12:01 -07:00
parent bb050910bb
commit 5e7915ae7a
13 changed files with 269 additions and 297 deletions
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2
src/util.h
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@ -203,7 +203,7 @@ extern std::string strstrip(std::string s);
extern bool hmac_key_set;
extern uint8_t shared_hmac_md5_key[16];
extern bool siphash_key_set;
extern highwayhash::SipHashState::Key shared_siphash_key;
extern highwayhash::HH_U64 shared_siphash_key[2];
extern void hmac_md5(size_t size, const unsigned char* bytes,
unsigned char digest[16]);