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recgen: Use salt when generating duplicate records

This commit is contained in:
Joris van Rantwijk 2022-06-27 20:01:08 +02:00
parent c47ff98883
commit eb3b06eede
1 changed files with 17 additions and 3 deletions
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20
src/recgen.cpp
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@ -111,8 +111,10 @@ public:
: m_record_size(record_size), : m_record_size(record_size),
m_bits_per_record(0), m_bits_per_record(0),
m_highbit_threshold(0), m_highbit_threshold(0),
m_salt(0),
m_flag_ascii(flag_ascii),
m_make_duplicates(false), m_make_duplicates(false),
m_flag_ascii(flag_ascii) m_salt_initialized(false)
{ {
assert(record_size > 0); assert(record_size > 0);
@ -226,6 +228,14 @@ public:
// Then use it to initialize a secondary random number generator. // Then use it to initialize a secondary random number generator.
// Then use that generator to generate the actual record. // Then use that generator to generate the actual record.
// During the first call, generate a salt for the secondary
// random number generator. Without this salt, every run
// would sample from the same subset of records.
if (!m_salt_initialized) {
m_salt = rng.next();
m_salt_initialized = true;
}
uint64_t s0 = 0, s1 = 0; uint64_t s0 = 0, s1 = 0;
unsigned int need_bits = m_bits_per_record; unsigned int need_bits = m_bits_per_record;
if (need_bits > 64) { if (need_bits > 64) {
@ -236,12 +246,14 @@ public:
s1 = rng.next(); s1 = rng.next();
} while (s1 > m_highbit_threshold); } while (s1 > m_highbit_threshold);
s1 >>= (64 - need_bits); s1 >>= (64 - need_bits);
s0 ^= m_salt;
// Create secondary random number generator.
Xoroshiro128plus rng2(s0, s1); Xoroshiro128plus rng2(s0, s1);
rng2.next(); rng2.next();
rng2.next(); rng2.next();
rng2.next();
// Use it to generate a record.
generate_uniform_record(record, rng2); generate_uniform_record(record, rng2);
} else { } else {
// Uniform distribution of records. // Uniform distribution of records.
@ -305,8 +317,10 @@ private:
unsigned int m_record_size; unsigned int m_record_size;
unsigned int m_bits_per_record; unsigned int m_bits_per_record;
uint64_t m_highbit_threshold; uint64_t m_highbit_threshold;
bool m_make_duplicates; uint64_t m_salt;
bool m_flag_ascii; bool m_flag_ascii;
bool m_make_duplicates;
bool m_salt_initialized;
}; };