It's a PRNG using the simple and fast xorshift method.
Signed-off-by: Michael Walle michael@walle.cc --- include/common.h | 4 ++++ lib/Makefile | 1 + lib/rand.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 3 files changed, 48 insertions(+), 0 deletions(-) create mode 100644 lib/rand.c
diff --git a/include/common.h b/include/common.h index 74d9704..1b6c3b0 100644 --- a/include/common.h +++ b/include/common.h @@ -740,6 +740,10 @@ char * strmhz(char *buf, unsigned long hz); /* lib/crc32.c */ #include <u-boot/crc.h>
+/* lib/rand.c */ +void srand(unsigned int seed); +unsigned int rand(void); + /* common/console.c */ int console_init_f(void); /* Before relocation; uses the serial stuff */ int console_init_r(void); /* After relocation; uses the console stuff */ diff --git a/lib/Makefile b/lib/Makefile index e6e6ec6..1672699 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -61,6 +61,7 @@ COBJS-y += string.o COBJS-y += time.o COBJS-$(CONFIG_BOOTP_PXE) += uuid.o COBJS-y += vsprintf.o +COBJS-y += rand.o
COBJS := $(COBJS-y) SRCS := $(COBJS:.o=.c) diff --git a/lib/rand.c b/lib/rand.c new file mode 100644 index 0000000..9923f67 --- /dev/null +++ b/lib/rand.c @@ -0,0 +1,43 @@ +/* + * Simple xorshift PRNG + * see http://www.jstatsoft.org/v08/i14/paper + * + * Copyright (c) 2012 Michael Walle + * Michael Walle michael@walle.cc + * + * See file CREDITS for list of people who contributed to this + * project. + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License as + * published by the Free Software Foundation; either version 2 of + * the License, or (at your option) any later version. + * + * This program 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 General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 59 Temple Place, Suite 330, Boston, + * MA 02111-1307 USA + */ + +#include <common.h> + +static unsigned int y = 2463534242U; + +void srand(unsigned int seed) +{ + y = seed; +} + +unsigned int rand(void) +{ + y ^= (y << 13); + y ^= (y >> 17); + y ^= (y << 5); + + return y; +}