runtime: seed fastrand() with hardware randomness

Author: dgryski

builder/sizes_test.go

@@ -42,8 +42,8 @@ func TestBinarySize(t *testing.T) {
 	tests := []sizeTest{
 		// microcontrollers
 		{"hifive1b", "examples/echo", 4484, 280, 0, 2252},
-		{"microbit", "examples/serial", 2732, 388, 8, 2256},
-		{"wioterminal", "examples/pininterrupt", 6016, 1484, 116, 6816},
+		{"microbit", "examples/serial", 2808, 388, 8, 2256},
+		{"wioterminal", "examples/pininterrupt", 6064, 1484, 116, 6816},
 
 		// TODO: also check wasm. Right now this is difficult, because
 		// wasm binaries are run through wasm-opt and therefore the

src/runtime/algorithm.go

@@ -23,7 +23,13 @@ func fastrand() uint32 {
 	return xorshift32State
 }
 
-var xorshift32State uint32 = 1
+func init() {
+	r, _ := hardwareRand()
+	xorshift64State = uint64(r | 1) // protect against 0
+	xorshift32State = uint32(xorshift64State)
+}
+
+var xorshift32State uint32
 
 func xorshift32(x uint32) uint32 {
 	// Algorithm "xor" from p. 4 of Marsaglia, "Xorshift RNGs".
@@ -43,7 +49,7 @@ func fastrand64() uint64 {
 	return xorshift64State
 }
 
-var xorshift64State uint64 = 1
+var xorshift64State uint64
 
 // 64-bit xorshift multiply rng from http://vigna.di.unimi.it/ftp/papers/xorshift.pdf
 func xorshiftMult64(x uint64) uint64 {