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glibc/stdlib/drand48-iter.c
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/* Copyright (C) 1995-2015 Free Software Foundation, Inc. | |
This file is part of the GNU C Library. | |
Contributed by Ulrich Drepper <drepper@gnu.ai.mit.edu>, August 1995. | |
The GNU C Library is free software; you can redistribute it and/or | |
modify it under the terms of the GNU Lesser General Public | |
License as published by the Free Software Foundation; either | |
version 2.1 of the License, or (at your option) any later version. | |
The GNU C Library is distributed in the hope that it will be useful, | |
but WITHOUT ANY WARRANTY; without even the implied warranty of | |
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
Lesser General Public License for more details. | |
You should have received a copy of the GNU Lesser General Public | |
License along with the GNU C Library; if not, see | |
<http://www.gnu.org/licenses/>. */ | |
#include <errno.h> | |
#include <stdlib.h> | |
#include <limits.h> | |
#include <stdint.h> | |
#include <sys/types.h> | |
/* Global state for non-reentrant functions. */ | |
struct drand48_data __libc_drand48_data; | |
int | |
__drand48_iterate (unsigned short int xsubi[3], struct drand48_data *buffer) | |
{ | |
uint64_t X; | |
uint64_t result; | |
/* Initialize buffer, if not yet done. */ | |
if (__glibc_unlikely (!buffer->__init)) | |
{ | |
buffer->__a = 0x5deece66dull; | |
buffer->__c = 0xb; | |
buffer->__init = 1; | |
} | |
/* Do the real work. We choose a data type which contains at least | |
48 bits. Because we compute the modulus it does not care how | |
many bits really are computed. */ | |
X = (uint64_t) xsubi[2] << 32 | (uint32_t) xsubi[1] << 16 | xsubi[0]; | |
result = X * buffer->__a + buffer->__c; | |
xsubi[0] = result & 0xffff; | |
xsubi[1] = (result >> 16) & 0xffff; | |
xsubi[2] = (result >> 32) & 0xffff; | |
return 0; | |
} |