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Move the ctime part of choose_array_element_by_weight into di_ops

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This way it gets the ctime options.
This commit is contained in:
Nick Mathewson 2016-04-27 10:33:46 -04:00
parent 20432fc541
commit e40cfc4425
3 changed files with 50 additions and 32 deletions
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45
src/common/di_ops.c
View File

@ -226,3 +226,48 @@ safe_mem_is_zero(const void *mem, size_t sz)
return 1 & ((total - 1) >> 8);
}
/** Time-invariant 64-bit greater-than; works on two integers in the range
* (0,INT64_MAX). */
#if SIZEOF_VOID_P == 8
#define gt_i64_timei(a,b) ((a) > (b))
#else
static inline int
gt_i64_timei(uint64_t a, uint64_t b)
{
int64_t diff = (int64_t) (b - a);
int res = diff >> 63;
return res & 1;
}
#endif
/**
* Given an array of list of <b>n_entries</b> uint64_t values, whose sum is
* <b>total</b>, find the first i such that the total of all elements 0...i is
* greater than rand_val.
*
* Try to perform this operation in a constant-time way.
*/
int
select_array_member_cumulative_timei(const uint64_t *entries, int n_entries,
uint64_t total, uint64_t rand_val)
{
int i, i_chosen=-1, n_chosen=0;
uint64_t total_so_far = 0;
for (i = 0; i < n_entries; ++i) {
total_so_far += entries[i];
if (gt_i64_timei(total_so_far, rand_val)) {
i_chosen = i;
n_chosen++;
/* Set rand_val to INT64_MAX rather than stopping the loop. This way,
* the time we spend in the loop does not leak which element we chose. */
rand_val = INT64_MAX;
}
}
tor_assert(total_so_far == total);
tor_assert(n_chosen == 1);
tor_assert(i_chosen >= 0);
tor_assert(i_chosen < n_entries);
return i_chosen;
}

2
src/common/di_ops.h
View File

@ -42,6 +42,8 @@ void dimap_add_entry(di_digest256_map_t **map,
const uint8_t *key, void *val);
void *dimap_search(const di_digest256_map_t *map, const uint8_t *key,
void *dflt_val);
int select_array_member_cumulative_timei(const uint64_t *entries, int n_entries,
uint64_t total, uint64_t rand_val);
#endif

35
src/or/routerlist.c
View File

@ -2103,20 +2103,6 @@ scale_array_elements_to_u64(uint64_t *entries_out, const double *entries_in,
#undef SCALE_TO_U64_MAX
}
/** Time-invariant 64-bit greater-than; works on two integers in the range
* (0,INT64_MAX). */
#if SIZEOF_VOID_P == 8
#define gt_i64_timei(a,b) ((a) > (b))
#else
static inline int
gt_i64_timei(uint64_t a, uint64_t b)
{
int64_t diff = (int64_t) (b - a);
int res = diff >> 63;
return res & 1;
}
#endif
/** Pick a random element of <b>n_entries</b>-element array <b>entries</b>,
* choosing each element with a probability proportional to its (uint64_t)
* value, and return the index of that element. If all elements are 0, choose
@ -2125,8 +2111,7 @@ gt_i64_timei(uint64_t a, uint64_t b)
STATIC int
choose_array_element_by_weight(const uint64_t *entries, int n_entries)
{
int i, i_chosen=-1, n_chosen=0;
uint64_t total_so_far = 0;
int i;
uint64_t rand_val;
uint64_t total = 0;
@ -2143,22 +2128,8 @@ choose_array_element_by_weight(const uint64_t *entries, int n_entries)
rand_val = crypto_rand_uint64(total);
for (i = 0; i < n_entries; ++i) {
total_so_far += entries[i];
if (gt_i64_timei(total_so_far, rand_val)) {
i_chosen = i;
n_chosen++;
/* Set rand_val to INT64_MAX rather than stopping the loop. This way,
* the time we spend in the loop does not leak which element we chose. */
rand_val = INT64_MAX;
}
}
tor_assert(total_so_far == total);
tor_assert(n_chosen == 1);
tor_assert(i_chosen >= 0);
tor_assert(i_chosen < n_entries);
return i_chosen;
return select_array_member_cumulative_timei(
entries, n_entries, total, rand_val);
}
/** When weighting bridges, enforce these values as lower and upper