pcg.cc (1683B)
1 /* 2 * PCG Random Number Generation for C. 3 * 4 * Copyright 2014 Melissa O'Neill <oneill@pcg-random.org> 5 * 6 * Licensed under the Apache License, Version 2.0 (the "License"); 7 * you may not use this file except in compliance with the License. 8 * You may obtain a copy of the License at 9 * 10 * http://www.apache.org/licenses/LICENSE-2.0 11 * 12 * Unless required by applicable law or agreed to in writing, software 13 * distributed under the License is distributed on an "AS IS" BASIS, 14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 15 * See the License for the specific language governing permissions and 16 * limitations under the License. 17 * 18 * For additional information about the PCG random number generation scheme, 19 * including its license and other licensing options, visit 20 * 21 * http://www.pcg-random.org 22 */ 23 24 /* 25 * This code is derived from the full C implementation, which is in turn 26 * derived from the canonical C++ PCG implementation. The C++ version 27 * has many additional features and is preferable if you can use C++ in 28 * your project. 29 */ 30 31 #include "rng/pcg.h" 32 33 PCG new_pcg() { 34 PCG pcg; 35 pcg.state = U64( 0x853c49e6748fea9b ); 36 pcg.inc = U64( 0xda3e39cb94b95bdb ); 37 return pcg; 38 } 39 40 PCG new_pcg( u64 state, u64 seq ) { 41 PCG pcg; 42 pcg.state = 0; 43 pcg.inc = ( seq << 1 ) | 1; 44 rng_next( &pcg ); 45 pcg.state += state; 46 rng_next( &pcg ); 47 return pcg; 48 } 49 50 u32 rng_next( PCG * pcg ) { 51 u64 oldstate = pcg->state; 52 pcg->state = oldstate * U64( 6364136223846793005 ) + pcg->inc; 53 u32 xorshifted = u32( ( ( oldstate >> 18 ) ^ oldstate ) >> 27 ); 54 u32 rot = u32( oldstate >> 59 ); 55 return ( xorshifted >> rot ) | ( xorshifted << ( ( -rot ) & 31 ) ); 56 }