From 2b8da4a254892e7c8d0d3fe93c6098976d30eab8 Mon Sep 17 00:00:00 2001 From: sears Date: Thu, 9 Jun 2011 00:02:20 +0000 Subject: [PATCH] comment, whitespace cleanup git-svn-id: svn+ssh://svn.corp.yahoo.com/yahoo/yrl/labs/pnuts/code/logstore@2664 8dad8b1f-cf64-0410-95b6-bcf113ffbcfe --- bloomFilter.c | 42 +++++++++++++++++++++++++----------------- bloomFilter.h | 9 ++++++--- 2 files changed, 31 insertions(+), 20 deletions(-) diff --git a/bloomFilter.c b/bloomFilter.c index ac6e08f..dffbed3 100644 --- a/bloomFilter.c +++ b/bloomFilter.c @@ -9,32 +9,37 @@ k: number of hash functions = ln(2) * (m/n) c: m/n f: false positive rate = (1/2)^k ~= 0.6185)^(m/n) ; - taking lof_0.6185 of both sides: k log_0.6185(1/2) = m/n ; + taking log_0.6185 of both sides: k log_0.6185(1/2) = m/n ; applying change of base: k log(1/2) / log(6.128) = m / n - (but that's not useful; this is:) + (but that's not useful; this is:) - f ~= 0.6185 ^ (m/n) - log_0.6185(f) = m/n - log(f) / log(0.6185) = m / n - m = n log f / log 0.6185 + f ~= 0.6185 ^ (m/n) + log_0.6185(f) = m/n + log(f) / log(0.6185) = m / n + m = n log f / log 0.6185 p: probability a given bit is 1 ~= e^(-kn/m) */ -static uint64_t bloom_filter_calc_num_buckets(uint64_t num_expected_items, double false_positive_rate) { - //m = n log f / log 0.6185 - return ((uint64_t) ceil(((double)num_expected_items) * log(false_positive_rate) / log(0.6185))); +static uint64_t bloom_filter_calc_num_buckets(uint64_t num_expected_items, + double false_positive_rate) { + // m = n log f / log 0.6185 + return ((uint64_t) ceil(((double)num_expected_items) * + log(false_positive_rate) / log(0.6185))); // m = - n ln f / ln 2 ^ 2 = - n ln f / 0.4804 = - n log f / (0.4343 * 0.4804) = -n log f / 0.2086 } -static int bloom_filter_calc_num_functions(uint64_t num_expected_items, uint64_t num_buckets) { +static int bloom_filter_calc_num_functions(uint64_t num_expected_items, + uint64_t num_buckets) { // k = ln(2) * (m/n) - int ret = floor((log(2) / log(exp(1.0))) * ((double) num_buckets) / (double) num_expected_items); + int ret = floor((log(2) / log(exp(1.0))) + * ((double) num_buckets) / (double) num_expected_items); if(ret == 0) { return 1; } else { return ret; } } -static double bloom_filter_current_false_positive_rate(uint64_t actual_number_of_items, uint64_t num_buckets) { +static double bloom_filter_current_false_positive_rate(uint64_t actual_number_of_items, + uint64_t num_buckets) { // 0.6185^(m/n) return pow(0.6185, ((double)num_buckets)/(double)actual_number_of_items); } @@ -71,7 +76,7 @@ void bloom_filter_destroy(bloom_filter_t* bf) { free(bf->result_scratch_space); free(bf); } -// XXX this uses %. It would be better if it used &, but that would potentially double the memory we use. #define a flag. +// TODO this uses %. It would be better if it used &, but that would potentially double the memory we use. #define a flag. static void bloom_filter_calc_functions(bloom_filter_t * bf, uint64_t* results, const char * key, int keylen) { uint64_t fa = bf->func_a(key, keylen); uint64_t fb = bf->func_b(key, keylen); @@ -125,8 +130,11 @@ void bloom_filter_print_stats(bloom_filter_t * bf) { printf("Design capacity %lld design false positive %f\n" "Current item count %lld current false positive %f\n" "Number of buckets %lld (%f MB), number of hash functions %lld\n", - bf->num_expected_items, bf->desired_false_positive_rate, - bf->actual_number_of_items, - bloom_filter_current_false_positive_rate(bf->actual_number_of_items, bf->num_buckets), - bf->num_buckets, ((double)bf->num_buckets) / (8.0 * 1024.0 * 1024.0), bf->num_functions); + (long long)bf->num_expected_items, bf->desired_false_positive_rate, + (long long)bf->actual_number_of_items, + bloom_filter_current_false_positive_rate(bf->actual_number_of_items, + bf->num_buckets), + (long long)bf->num_buckets, + ((double)bf->num_buckets) / (8.0 * 1024.0 * 1024.0), + (long long)bf->num_functions); } diff --git a/bloomFilter.h b/bloomFilter.h index cb12f9c..90eeb7f 100644 --- a/bloomFilter.h +++ b/bloomFilter.h @@ -8,10 +8,13 @@ BEGIN_C_DECLS typedef struct bloom_filter_t bloom_filter_t; /** - @return 0 if there is not enough memory, or some other error occurred; a pointer to the new bloom filter otherwise. + @return 0 if there is not enough memory, or some other error occurred; a + pointer to the new bloom filter otherwise. */ -bloom_filter_t * bloom_filter_create(uint64_t(*hash_func_a)(const char*,int), uint64_t(*hash_func_b)(const char*,int), - uint64_t num_expected_items, double false_positive_rate); +bloom_filter_t * bloom_filter_create(uint64_t(*hash_func_a)(const char*,int), + uint64_t(*hash_func_b)(const char*,int), + uint64_t num_expected_items, + double false_positive_rate); void bloom_filter_destroy(bloom_filter_t*);