84f7cdb0c5
Rename prn to prng so that Windows doesn't choke when trying to create a file named prn.h.
61 lines
2.0 KiB
C
61 lines
2.0 KiB
C
/******************************************************************************/
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#ifdef JEMALLOC_H_TYPES
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/*
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* Simple linear congruential pseudo-random number generator:
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*
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* prng(y) = (a*x + c) % m
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*
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* where the following constants ensure maximal period:
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*
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* a == Odd number (relatively prime to 2^n), and (a-1) is a multiple of 4.
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* c == Odd number (relatively prime to 2^n).
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* m == 2^32
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*
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* See Knuth's TAOCP 3rd Ed., Vol. 2, pg. 17 for details on these constraints.
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*
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* This choice of m has the disadvantage that the quality of the bits is
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* proportional to bit position. For example. the lowest bit has a cycle of 2,
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* the next has a cycle of 4, etc. For this reason, we prefer to use the upper
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* bits.
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*
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* Macro parameters:
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* uint32_t r : Result.
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* unsigned lg_range : (0..32], number of least significant bits to return.
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* uint32_t state : Seed value.
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* const uint32_t a, c : See above discussion.
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*/
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#define prng32(r, lg_range, state, a, c) do { \
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assert(lg_range > 0); \
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assert(lg_range <= 32); \
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\
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r = (state * (a)) + (c); \
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state = r; \
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r >>= (32 - lg_range); \
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} while (false)
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/* Same as prng32(), but 64 bits of pseudo-randomness, using uint64_t. */
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#define prng64(r, lg_range, state, a, c) do { \
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assert(lg_range > 0); \
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assert(lg_range <= 64); \
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\
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r = (state * (a)) + (c); \
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state = r; \
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r >>= (64 - lg_range); \
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} while (false)
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#endif /* JEMALLOC_H_TYPES */
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/******************************************************************************/
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#ifdef JEMALLOC_H_STRUCTS
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#endif /* JEMALLOC_H_STRUCTS */
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/******************************************************************************/
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#ifdef JEMALLOC_H_EXTERNS
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#endif /* JEMALLOC_H_EXTERNS */
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/******************************************************************************/
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#ifdef JEMALLOC_H_INLINES
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#endif /* JEMALLOC_H_INLINES */
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/******************************************************************************/
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