[bugfix] Fix calibration for 32 bit systems (#7)

* Use smaller constant for tests with invalid N. This fixes the tests on 32 bit systems.
* Fix comparison for 32 bit systems. This closes #6

scrypt.go

@@ -260,7 +260,7 @@ func Calibrate(timeout time.Duration, memMiBytes int, params Params) (Params, er
 	var again bool
 	memBytes := memMiBytes << 20
 	// If we'd use more memory then the allowed, we can tune the memory usage
-	for 128*p.R*p.N > memBytes {
+	for 128*int64(p.R)*int64(p.N) > int64(memBytes) {
 		if p.R > 1 {
 			// by lowering r
 			p.R--

scrypt_test.go

@@ -23,11 +23,11 @@ var testParams = []struct {
 	{true, Params{1048576, 8, 2, 64, 128}},
 	{false, Params{-1, 8, 1, 16, 32}},          // invalid N
 	{false, Params{0, 8, 1, 16, 32}},           // invalid N
-	{false, Params{1 << 31, 8, 1, 16, 32}},     // invalid N
+	{false, Params{1<<31 - 1, 8, 1, 16, 32}},   // invalid N
 	{false, Params{16384, 0, 12, 16, 32}},      // invalid R
 	{false, Params{16384, 8, 0, 16, 32}},       // invalid R > maxInt/128/P
 	{false, Params{16384, 1 << 24, 1, 16, 32}}, // invalid R > maxInt/256
-	{false, Params{1 << 31, 8, 0, 16, 32}},     // invalid p < 0
+	{false, Params{1<<31 - 1, 8, 0, 16, 32}},   // invalid p < 0
 	{false, Params{4096, 8, 1, 5, 32}},         // invalid SaltLen
 	{false, Params{4096, 8, 1, 16, 2}},         // invalid DKLen
 }