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