diff options
Diffstat (limited to 'src/common')
| -rw-r--r-- | src/common/util.c | 20 | ||||
| -rw-r--r-- | src/common/util.h | 2 |
2 files changed, 16 insertions, 6 deletions
diff --git a/src/common/util.c b/src/common/util.c index f7baab0791..be866a5fe6 100644 --- a/src/common/util.c +++ b/src/common/util.c @@ -527,15 +527,25 @@ round_int64_to_next_multiple_of(int64_t number, int64_t divisor) /** Transform a random value <b>p</b> from the uniform distribution in * [0.0, 1.0[ into a Laplace distributed value with location parameter - * <b>mu</b> and scale parameter <b>b</b> in [-Inf, Inf[. */ -double + * <b>mu</b> and scale parameter <b>b</b>. Truncate the final result + * to be an integer in [INT64_MIN, INT64_MAX]. */ +int64_t sample_laplace_distribution(double mu, double b, double p) { + double result; + tor_assert(p >= 0.0 && p < 1.0); /* This is the "inverse cumulative distribution function" from: * http://en.wikipedia.org/wiki/Laplace_distribution */ - return mu - b * (p > 0.5 ? 1.0 : -1.0) - * tor_mathlog(1.0 - 2.0 * fabs(p - 0.5)); + result = mu - b * (p > 0.5 ? 1.0 : -1.0) + * tor_mathlog(1.0 - 2.0 * fabs(p - 0.5)); + + if (result >= INT64_MAX) + return INT64_MAX; + else if (result <= INT64_MIN) + return INT64_MIN; + else + return (int64_t) result; } /** Add random noise between INT64_MIN and INT64_MAX coming from a @@ -546,10 +556,10 @@ int64_t add_laplace_noise(int64_t signal, double random, double delta_f, double epsilon) { - /* cast to int64_t intended */ int64_t noise = sample_laplace_distribution( 0.0, /* just add noise, no further signal */ delta_f / epsilon, random); + if (noise > 0 && INT64_MAX - noise < signal) return INT64_MAX; else if (noise < 0 && INT64_MIN - noise > signal) diff --git a/src/common/util.h b/src/common/util.h index 1b8fc74db5..89c140032a 100644 --- a/src/common/util.h +++ b/src/common/util.h @@ -173,7 +173,7 @@ unsigned round_to_next_multiple_of(unsigned number, unsigned divisor); uint32_t round_uint32_to_next_multiple_of(uint32_t number, uint32_t divisor); uint64_t round_uint64_to_next_multiple_of(uint64_t number, uint64_t divisor); int64_t round_int64_to_next_multiple_of(int64_t number, int64_t divisor); -double sample_laplace_distribution(double mu, double b, double p); +int64_t sample_laplace_distribution(double mu, double b, double p); int64_t add_laplace_noise(int64_t signal, double random, double delta_f, double epsilon); int n_bits_set_u8(uint8_t v); |