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