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awk: improve random number generation

don't use rand() and scale it to 0..1, instead call
native frand() which produces uniform random number.

instead of seeding the rng with time(0), use truerand().

--- a/sys/src/cmd/awk/run.c

+++ b/sys/src/cmd/awk/run.c

@@ -29,10 +29,6 @@

 #include "awk.h"

 #include "y.tab.h"

-#ifndef RAND_MAX

-#define RAND_MAX	32767	/* all that ansi guarantees */

-#endif

-

 jmp_buf env;

 extern	int	pairstack[];

@@ -1582,12 +1578,11 @@

 		u = (Awkfloat) system(getsval(x));

 		break;

 	case FRAND:

-		/* in principle, rand() returns something in 0..RAND_MAX */

-		u = (Awkfloat) (rand() % RAND_MAX) / RAND_MAX;

+		u = frand();

 		break;

 	case FSRAND:

 		if (isrec(x))	/* no argument provided */

-			u = time(nil);

+			u = (Awkfloat) (truerand() >> 1);

 		else

 			u = getfval(x);

 		srand((unsigned int) u);

-- 

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