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kernel: xoroshiro128+ generator for rand()/nrand()

the kernels custom rand() and nrand() functions where not working
as specified in rand(2). now we just use libc's rand() and nrand()
functions but provide a custom lrand() impelmenting the xoroshiro128+
algorithm as proposed by aiju.

--- a/sys/src/9/port/devcons.c

+++ b/sys/src/9/port/devcons.c

@@ -845,24 +845,6 @@

 	devwstat,

 };

-static	ulong	randn;

-

-int

-rand(void)

-{

-	if(randn == 0)

-		randomread((void*)&randn, sizeof(randn));

-	randn = randn*1103515245 + 12345 + MACHP(0)->ticks;

-	return randn;

-}

-

-int

-nrand(int n)

-{

-	rand();

-	return (randn>>16) % n;

-}

-

 static uvlong uvorder = 0x0001020304050607ULL;

 static uchar*

--- a/sys/src/9/port/lib.h

+++ b/sys/src/9/port/lib.h

@@ -52,6 +52,14 @@

 extern	int	utfnlen(char*, long);

 extern	int	runelen(long);

+/*

+ * random number

+ */

+extern	int	rand(void);

+extern	int	nrand(int);

+extern	long	lrand(void);

+extern	long	lnrand(long);

+

 extern	int	abs(int);

 /*

--- a/sys/src/9/port/portfns.h

+++ b/sys/src/9/port/portfns.h

@@ -200,7 +200,6 @@

 Proc*		newproc(void);

 void		nexterror(void);

 int		notify(Ureg*);

-int		nrand(int);

 uvlong		ns2fastticks(uvlong);

 int		okaddr(uintptr, ulong, int);

 int		openmode(ulong);

@@ -284,7 +283,6 @@

 int		qwindow(Queue*);

 int		qwrite(Queue*, void*, int);

 void		qnoblock(Queue*, int);

-int		rand(void);

 void		randominit(void);

 ulong		randomread(void*, ulong);

 void		rdb(void);

--- a/sys/src/9/port/random.c

+++ b/sys/src/9/port/random.c

@@ -120,3 +120,28 @@

 {

 	randomread(p, n);

 }

+

+/* used by rand(),nrand() */

+long

+lrand(void)

+{

+	/* xoroshiro128+ algorithm */

+	static int seeded = 0;

+	static uvlong s[2];

+	static Lock lk;

+	ulong r;

+

+	if(seeded == 0){

+		randomread(s, sizeof(s));

+		seeded = (s[0] | s[1]) != 0;

+	}

+

+	lock(&lk);

+	r = (s[0] + s[1]) >> 33;

+	s[1] ^= s[0];

+ 	s[0] = (s[0] << 55 | s[0] >> 9) ^ s[1] ^ (s[1] << 14);

+ 	s[1] = (s[1] << 36 | s[1] >> 28);

+	unlock(&lk);

+

+ 	return r;

+}