mirror of https://github.com/libsdl-org/SDL.git
81 lines
2.3 KiB
C
81 lines
2.3 KiB
C
/*
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Simple DirectMedia Layer
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Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
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This software is provided 'as-is', without any express or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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1. The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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2. Altered source versions must be plainly marked as such, and must not be
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misrepresented as being the original software.
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3. This notice may not be removed or altered from any source distribution.
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*/
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#include "SDL_internal.h"
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/* This file contains portable random functions for SDL */
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static Uint64 SDL_rand_state;
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void SDL_srand(Uint64 seed)
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{
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SDL_rand_state = seed;
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}
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Uint32 SDL_rand(void)
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{
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return SDL_rand_r(&SDL_rand_state);
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}
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/*
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* Return a number between [0, n)
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* Fast but slightly biased. Don't run your casino with this.
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*/
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Sint32 SDL_rand_n(Sint32 n)
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{
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// On 32-bit arch, the compiler will optimize to a single 32-bit multiply
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Uint64 val = (Uint64)SDL_rand() * n;
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return (Sint32)(val >> 32);
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}
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/*
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* Random float in range [0,1)
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*/
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float SDL_rand_float(void)
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{
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return (SDL_rand() >> (32-24)) * 0x1p-24f;
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}
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/* A fast psuedo-random number generator.
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* Not suitable for cryptography or gambling
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*/
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Uint32 SDL_rand_r(Uint64 *state)
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{
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if (!state) {
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return 0;
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}
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if (!*state) {
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*state = SDL_GetPerformanceCounter();
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}
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// Multiplier from Table 6 of
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// Steele GL, Vigna S. Computationally easy, spectrally good multipliers
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// for congruential pseudorandom number generators.
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// Softw Pract Exper. 2022;52(2):443-458. doi: 10.1002/spe.3030
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// 32-bit 'a' improves performance on 32-bit architectures
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// 'c' can be any odd number, but < 256 generates smaller code on some arch
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*state = *state * 0xf9b25d65ul + 0xFD;
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// Only return top 32 bits because they have a longer period
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return (Uint32)(*state >> 32);
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}
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