add bittwiddling64 test

tests/bittwiddling64.c

@@ -0,0 +1,106 @@
+void
+out( char c ) {
+	*((char*) 0x20000) = c;
+}
+
+//#include <stdio.h>
+//#define out( c ) putchar( c )
+
+void
+print( char* s ) {
+	while (*s)
+		out( *s++ );
+}
+
+void
+println() {
+	out( '\n' );
+}
+
+char*
+bin2str( long n, int radix, char* buf ) {
+	char digits[] = "0123456789ABCDEF";
+	char* p = &buf[33];
+	long quo = n;
+
+	if (n < 0)
+		quo = -quo;
+
+	*p-- = 0;
+
+	while (quo >= radix) {
+		*p-- = digits[(quo%radix)];
+		quo /= radix;
+	}
+
+	*p = digits[quo];
+
+	if (n < 0)
+		*--p = '-';
+
+	return p;
+}
+
+void
+printn( long n ) {
+	char buf[34];
+	char* s = bin2str( n, 16, buf );
+
+	print( s );
+}
+
+long
+abs( long x ) {
+  const long bit31 = x >> 63;
+
+  return (x ^ bit31) - bit31;
+}
+
+long
+modifyBit( long x, unsigned char position, int newState ) {
+  long mask = 1 << position;
+  long state = newState;
+
+  return (x & ~mask) | (-state & mask);
+}
+
+long
+flipBit( long x, unsigned char position ) {
+  long mask = 1 << position;
+
+  return x ^ mask;
+}
+
+long
+isNegative( long n ) {
+	return (long)((unsigned long) n >> 63);
+}
+
+void
+main() {
+	printn( abs(5) );
+	print( ", " );
+	printn( abs(0) );
+	print( ", " );
+	printn( abs(-5) );
+	println();
+
+	printn( modifyBit(0, 5, 0) );//0
+	print( ", " );
+	printn( modifyBit(0, 5, 1) );//0x20
+	print( ", " );
+	printn( modifyBit(0x77, 5, 0) );//0x57
+	print( ", " );
+	printn( modifyBit(0x77, 5, 1) );//0x77
+	println();
+
+	printn( flipBit(0, 5) );//20
+	print( ", " );
+	printn( flipBit(0x77, 5) );//57
+	println();
+
+	printn( isNegative(0) );
+	print( ", " );
+	printn( isNegative(-5) );
+	println();
+}