ref: 1fe2c325416d8affab446a50397da8b43f1a57c6
dir: /sys/src/cmd/unix/drawterm/libc/lnrand.c/
#include <u.h>
#include <libc.h>
#define MASK 0x7fffffffL
long
lnrand(long n)
{
long slop, v;
if(n < 0)
return n;
slop = MASK % n;
do
v = lrand();
while(v <= slop);
return v % n;
}