worldgen: add vanilla biome search and decoration RNG

internal/worldgen/simplex_noise_test.go

@@ -0,0 +1,25 @@
+package worldgen
+
+import (
+	"math"
+	"testing"
+)
+
+func TestBiomeInfoNoiseVanillaVectors(t *testing.T) {
+	tests := []struct {
+		x, z int
+		want float64
+	}{
+		{0, 0, 0},
+		{16, 0, 0.6210549241139091},
+		{0, 16, -0.005784055694146521},
+		{-16, -16, -0.3789716250634575},
+		{123, 456, 0.43256906665489797},
+	}
+	for _, test := range tests {
+		got := BiomeInfoNoise(float64(test.x)/80, float64(test.z)/80)
+		if math.Float64bits(got) != math.Float64bits(test.want) {
+			t.Errorf("BiomeInfoNoise(%d,%d) = %.17g, want %.17g", test.x, test.z, got, test.want)
+		}
+	}
+}