USE SIZEOF_LONG for high bit grab from random()

ChangeLog

@@ -23,6 +23,7 @@ Version NEXT
 	parsecheck: report if all tests passed / some failed
 	parsecheck: init all fields in testcase results
 	SConstruct: declare CPP constant SIZEOF_LONG
+	randomcheck: use SIZEOF_LONG for grabing highest bits from long()
 
 Version 2.8.1b29 - 24 Aug 2019
 	added scons command line argument without-fspscan=yes for building

tests/randomcheck.c

@@ -9,6 +9,12 @@ static int rounds;
 static int result;
 #define MAX_WORST_ALLOWED 0.1f
 
+/**
+Tests how to get 16 bit unsigned short number
+from long random(void) function without
+losing randomness
+*/
+
 /* FSP classic algo */
 static unsigned short classic (void)
 {
@@ -26,10 +32,19 @@ static unsigned short simple (void)
   return random();
 }
 
-/* get high bits from random result - better */
+/* get high bits from random() result.
+
+In most classic random implementations used in libc
+highest bits have better randomness.
+
+In modern random() generators there should be no difference.
+*/
 static unsigned short simple2 (void)
 {
-  return (random() >> 15);
+  /* we assume that our return value is 16 bits long
+     and random() returns only positive long integers
+  */   	
+  return ( random() >> (SIZEOF_LONG*8 - 16 - 1) );
 }
 
 /* The following algorithm is recommended by Numerical Recipies: */