refine precision limits on unsafe_math (#3589)

lib/compress.js

@@ -2953,7 +2953,8 @@ merge(Compressor.prototype, {
                 && typeof result == "number"
                 && (this.operator == "+" || this.operator == "-")) {
                 var digits = Math.max(0, decimals(left), decimals(right));
-                if (digits < 21) return +result.toFixed(digits);
+                // 53-bit significand => 15.95 decimal places
+                if (digits < 16) return +result.toFixed(digits);
             }
             return result;
 

test/compress/numbers.js

@@ -917,3 +917,17 @@ issue_3547_4: {
         "number 0",
     ]
 }
+
+unsafe_math_rounding: {
+    options = {
+        evaluate: true,
+        unsafe_math: true,
+    }
+    input: {
+        console.log(4 / -3 + 1 === 1 / -3);
+    }
+    expect: {
+        console.log(false);
+    }
+    expect_stdout: "false"
+}