154 lines
3.9 KiB
C
154 lines
3.9 KiB
C
/* Single-header LCG random generator and faster-than-modulo rand_until, rand_between */
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/* LICENCE: Feel free to use it but please mention MagosIT Kft or its youtube channel */
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#ifndef FAST_RAND_H
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#define FAST_RAND_H
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#include <stdint.h>
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#include <assert.h>
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#ifndef NO_CSTDLIB
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#include <stdlib.h>
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#endif /* NO_CSTDLIB */
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#ifdef __cplusplus
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// C++-specific logic
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#if defined(__GNUC__) || defined(__clang__)
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#define restrict __restrict__ // GCC/Clang
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#elif defined(_MSC_VER)
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#define restrict __restrict // MSVC
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#else
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#error "Compiler not supported for 'restrict' keyword in C++"
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#endif
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#endif
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/* Currently a single integer is enough */
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typedef uint32_t rand_state;
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/* Currently a single integer is enough */
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struct rand_ilp_state {
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uint32_t a;
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uint32_t b;
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uint32_t c;
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uint32_t d;
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uint32_t e;
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uint32_t f;
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uint32_t g;
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uint32_t h;
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};
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typedef struct rand_ilp_state rand_ilp_state;
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/** Creates a random number generator state with given seed */
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static inline rand_state init_rand_with(uint32_t seed) {
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return seed;
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}
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static inline rand_ilp_state init_rand_ilp_with(
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uint32_t seed1,
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uint32_t seed2,
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uint32_t seed3,
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uint32_t seed4,
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uint32_t seed5,
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uint32_t seed6,
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uint32_t seed7,
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uint32_t seed8) {
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rand_ilp_state ret;
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ret.a = seed1;
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ret.b = seed2;
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ret.c = seed3;
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ret.d = seed4;
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ret.e = seed1;
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ret.f = seed2;
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ret.g = seed3;
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ret.h = seed4;
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return ret;
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}
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#ifndef NO_CSTDLIB
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/** Creates a random number generator state with arc4random() which does not need seeding as it uses system etropy */
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static inline rand_state init_rand() {
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return arc4random();
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}
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/** Creates a random number generator state with arc4random() which does not need seeding as it uses system etropy */
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static inline rand_ilp_state init_rand_ilp() {
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rand_ilp_state ret;
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ret.a = arc4random();
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ret.b = arc4random();
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ret.c = arc4random();
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ret.d = arc4random();
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ret.e = arc4random();
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ret.f = arc4random();
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ret.g = arc4random();
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ret.h = arc4random();
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return ret;
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}
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#endif /* NO_CSTDLIB */
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// 32-bit LCG
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static inline uint32_t lcg(rand_state *state) {
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*state = *state * 1664525u + 1013904223u;
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return *state;
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}
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#define RAND_ILP_MAX 7
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enum RAND_ILP {
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A = 0, B = 1, C = 2, D = 3,
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E = 4, F = 5, G = 6, H = RAND_ILP_MAX
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};
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typedef enum RAND_ILP RAND_ILP;
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// 32-bit LCG with more states - might be faster when called from a loop, see perf.cpp
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static inline uint32_t lcg_ilp(rand_ilp_state *state, RAND_ILP which) {
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if(which == A) {
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state->a = state->a * 1664525u + 1013904223u;
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return state->a;
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} else if(which == B) {
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state->b = state->b * 1664525u + 1013904223u;
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return state->b;
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} else if(which == C) {
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state->c = state->c * 1664525u + 1013904223u;
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return state->c;
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} else if(which == D) {
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state->d = state->d * 1664525u + 1013904223u;
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return state->d;
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} else if(which == E) {
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state->e = state->e * 1664525u + 1013904223u;
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return state->e;
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} else if(which == F) {
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state->f = state->f * 1664525u + 1013904223u;
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return state->f;
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} else if(which == G) {
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state->g = state->g * 1664525u + 1013904223u;
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return state->g;
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} else if(which == H) {
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state->h = state->h * 1664525u + 1013904223u;
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return state->h;
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}
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assert(0);
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}
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/** Pick a "reasonably random" number in [0, until-1] without modulus */
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static inline uint32_t rand_until(rand_state *restrict state, uint32_t until) {
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uint32_t rand = lcg(state);
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// Multiply by "until", take the upper 32 bits of the 64-bit result
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return (uint32_t)(((uint64_t)rand * until) >> 32);
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}
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uint32_t fastmodlike(uint32_t num, uint32_t m) {
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return (((uint64_t) num) * m);
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}
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/**
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* Pick a "reasonably random" number in [from, to) without modulus.
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*
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* @param state The random state - See: init_rand() and init_rand_with(seed)
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* @param from The smallest possible value
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* @param to The biggest possible value + 1
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* @returns A value in [from, to) interval
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*/
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static inline uint32_t rand_between(rand_state *restrict state, uint32_t from, uint32_t to) {
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return from + rand_until(state, to - from);
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}
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#endif /* FAST_RAND_H */
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