1#include "jemalloc/internal/jemalloc_preamble.h"
2#include "jemalloc/internal/jemalloc_internal_includes.h"
3
4/*
5 * To avoid using floating point math down core paths (still necessary because
6 * versions of the glibc dynamic loader that did not preserve xmm registers are
7 * still somewhat common, requiring us to be compilable with -mno-sse), and also
8 * to avoid generally expensive library calls, we use a precomputed table of
9 * values. We want to sample U uniformly on [0, 1], and then compute
10 * ceil(log(u)/log(1-1/nticks)). We're mostly interested in the case where
11 * nticks is reasonably big, so 1/log(1-1/nticks) is well-approximated by
12 * -nticks.
13 *
14 * To compute log(u), we sample an integer in [1, 64] and divide, then just look
15 * up results in a table. As a space-compression mechanism, we store these as
16 * uint8_t by dividing the range (255) by the highest-magnitude value the log
17 * can take on, and using that as a multiplier. We then have to divide by that
18 * multiplier at the end of the computation.
19 *
20 * The values here are computed in src/ticker.py
21 */
22
23const uint8_t ticker_geom_table[1 << TICKER_GEOM_NBITS] = {
24 254, 211, 187, 169, 156, 144, 135, 127,
25 120, 113, 107, 102, 97, 93, 89, 85,
26 81, 77, 74, 71, 68, 65, 62, 60,
27 57, 55, 53, 50, 48, 46, 44, 42,
28 40, 39, 37, 35, 33, 32, 30, 29,
29 27, 26, 24, 23, 21, 20, 19, 18,
30 16, 15, 14, 13, 12, 10, 9, 8,
31 7, 6, 5, 4, 3, 2, 1, 0
32};
33