diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
index a5376cda9..4b261f748 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TAbstractStringBuilder.java
@@ -194,18 +194,20 @@ class TAbstractStringBuilder implements TSerializable, TCharSequence {
 
     protected TAbstractStringBuilder insert(int target, float value) {
         if (value == 0) {
-            insertSpace(target, target + 3);
-            buffer[target++] = '0';
-            buffer[target++] = '.';
-            buffer[target++] = '0';
-            return this;
-        } else if (value == -0) {
-            insertSpace(target, target + 4);
-            buffer[target++] = '-';
-            buffer[target++] = '0';
-            buffer[target++] = '.';
-            buffer[target++] = '0';
-            return this;
+            if (1 / value == Float.POSITIVE_INFINITY) {
+                insertSpace(target, target + 3);
+                buffer[target++] = '0';
+                buffer[target++] = '.';
+                buffer[target++] = '0';
+                return this;
+            } else {
+                insertSpace(target, target + 4);
+                buffer[target++] = '-';
+                buffer[target++] = '0';
+                buffer[target++] = '.';
+                buffer[target++] = '0';
+                return this;
+            }
         } else if (Float.isNaN(value)) {
             insertSpace(target, target + 3);
             buffer[target++] = 'N';
@@ -330,18 +332,20 @@ class TAbstractStringBuilder implements TSerializable, TCharSequence {
 
     protected TAbstractStringBuilder insert(int target, double value) {
         if (value == 0) {
-            insertSpace(target, target + 3);
-            buffer[target++] = '0';
-            buffer[target++] = '.';
-            buffer[target++] = '0';
-            return this;
-        } else if (value == -0) {
-            insertSpace(target, target + 4);
-            buffer[target++] = '-';
-            buffer[target++] = '0';
-            buffer[target++] = '.';
-            buffer[target++] = '0';
-            return this;
+            if (1 / value == Double.POSITIVE_INFINITY) {
+                insertSpace(target, target + 3);
+                buffer[target++] = '0';
+                buffer[target++] = '.';
+                buffer[target++] = '0';
+                return this;
+            } else {
+                insertSpace(target, target + 4);
+                buffer[target++] = '-';
+                buffer[target++] = '0';
+                buffer[target++] = '.';
+                buffer[target++] = '0';
+                return this;
+            }
         } else if (Double.isNaN(value)) {
             insertSpace(target, target + 3);
             buffer[target++] = 'N';
diff --git a/classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java b/classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java
index 95c7b5977..d693bd410 100644
--- a/classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java
+++ b/classlib/src/main/java/org/teavm/classlib/java/lang/TMath.java
@@ -344,29 +344,25 @@ public final class TMath extends TObject {
     }
 
     public static float copySign(float magnitude, float sign) {
-        if (sign == 0 || sign == -0) {
-            return sign;
-        }
-        return (sign > 0) == (magnitude > 0) ? magnitude : -magnitude;
+        return Float.intBitsToFloat((Float.floatToRawIntBits(sign) & Integer.MIN_VALUE)
+                | (Float.floatToRawIntBits(magnitude) & Integer.MAX_VALUE));
     }
 
     public static double copySign(double magnitude, double sign) {
-        if (sign == 0 || sign == -0) {
-            return sign;
-        }
-        return (sign > 0) == (magnitude > 0) ? magnitude : -magnitude;
+        return Double.longBitsToDouble((Double.doubleToRawLongBits(sign) & Long.MIN_VALUE)
+                | (Double.doubleToRawLongBits(magnitude) & Long.MAX_VALUE));
     }
 
     public static int getExponent(double d) {
-        long bits = TDouble.doubleToLongBits(d);
+        long bits = TDouble.doubleToRawLongBits(d);
         int exponent = (int) ((bits >> 52) & 0x7FF);
         return exponent - 1023;
     }
 
     public static int getExponent(float f) {
-        int bits = TFloat.floatToIntBits(f);
-        int exponent = (bits >> 23) & 0xF;
-        return exponent + 128;
+        int bits = TFloat.floatToRawIntBits(f);
+        int exponent = (bits >> 23) & 0xFF;
+        return exponent - 127;
     }
 
     public static double nextAfter(double start, double direction) {
diff --git a/tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java b/tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java
index 0c15c914f..afab53c09 100644
--- a/tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java
+++ b/tests/src/test/java/org/teavm/classlib/java/lang/MathTest.java
@@ -94,6 +94,20 @@ public class MathTest {
         assertEquals(Float.valueOf(1), Float.valueOf(Math.signum(Float.POSITIVE_INFINITY)));
     }
 
+    @Test
+    public void copySignWorks() {
+        assertEquals(Double.valueOf(1.0), Double.valueOf(Math.copySign(1.0, 0.0)));
+        assertEquals(Double.valueOf(-1.0), Double.valueOf(Math.copySign(1.0, -0.0)));
+        assertEquals(Double.valueOf(1.0), Double.valueOf(Math.copySign(1.0, Double.NaN)));
+        assertEquals(Double.valueOf(Double.NaN), Double.valueOf(Math.copySign(Double.NaN, -1.0)));
+        assertEquals(Double.valueOf(Double.POSITIVE_INFINITY), Double.valueOf(Math.copySign(Double.NEGATIVE_INFINITY, 1.0)));
+        assertEquals(Float.valueOf(1.0f), Float.valueOf(Math.copySign(1.0f, 0.0f)));
+        assertEquals(Float.valueOf(-1.0f), Float.valueOf(Math.copySign(1.0f, -0.0f)));
+        assertEquals(Float.valueOf(1.0f), Float.valueOf(Math.copySign(1.0f, Float.NaN)));
+        assertEquals(Float.valueOf(Float.NaN), Float.valueOf(Math.copySign(Float.NaN, -1.0f)));
+        assertEquals(Float.valueOf(Float.POSITIVE_INFINITY), Float.valueOf(Math.copySign(Float.NEGATIVE_INFINITY, 1.0f)));
+    }
+
     @Test
     public void roundWorks() {
         assertEquals(1, Math.round(1.3));
@@ -133,4 +147,20 @@ public class MathTest {
         assertEquals(Double.valueOf(Double.longBitsToDouble(Double.doubleToLongBits(Double.NEGATIVE_INFINITY) - 1)),
                 Double.valueOf(Math.nextUp(Double.NEGATIVE_INFINITY)));
     }
+
+    @Test
+    public void exponentWorks() {
+        assertEquals(0, Math.getExponent(1.0f));
+        assertEquals(-127, Math.getExponent(Float.MIN_VALUE));
+        assertEquals(127, Math.getExponent(Float.MAX_VALUE));
+        assertEquals(128, Math.getExponent(Float.POSITIVE_INFINITY));
+        assertEquals(128, Math.getExponent(Float.NEGATIVE_INFINITY));
+        assertEquals(128, Math.getExponent(Float.NaN));
+        assertEquals(0, Math.getExponent(1.0));
+        assertEquals(-1023, Math.getExponent(Double.MIN_VALUE));
+        assertEquals(1023, Math.getExponent(Double.MAX_VALUE));
+        assertEquals(1024, Math.getExponent(Double.POSITIVE_INFINITY));
+        assertEquals(1024, Math.getExponent(Double.NEGATIVE_INFINITY));
+        assertEquals(1024, Math.getExponent(Double.NaN));
+    }
 }
diff --git a/tests/src/test/java/org/teavm/classlib/java/lang/StringBuilderTest.java b/tests/src/test/java/org/teavm/classlib/java/lang/StringBuilderTest.java
index f2710dc81..266ef4725 100644
--- a/tests/src/test/java/org/teavm/classlib/java/lang/StringBuilderTest.java
+++ b/tests/src/test/java/org/teavm/classlib/java/lang/StringBuilderTest.java
@@ -78,13 +78,14 @@ public class StringBuilderTest {
                 .append(" ").append(1200f)
                 .append(" ").append(0.023f)
                 .append(" ").append(0f)
+                .append(" ").append(-0.0f)
                 .append(" ").append(1f)
                 .append(" ").append(Float.NaN)
                 .append(" ").append(Float.POSITIVE_INFINITY)
                 .append(" ").append(Float.NEGATIVE_INFINITY);
         assertEquals("1.234E25 9.8765E30 -1.234E25 -9.8765E30 3.402823E38"
                 + " 1.234E-25 9.8764E-30 -1.234E-25 -9.8764E-30 1.17549E-38"
-                + " 1200.0 0.023 0.0 1.0 NaN Infinity -Infinity", sb.toString());
+                + " 1200.0 0.023 0.0 -0.0 1.0 NaN Infinity -Infinity", sb.toString());
     }
 
     @Test
@@ -107,6 +108,7 @@ public class StringBuilderTest {
                 .append(" ").append(1200.0)
                 .append(" ").append(0.023)
                 .append(" ").append(0.0)
+                .append(" ").append(-0.0)
                 .append(" ").append(1.0)
                 .append(" ").append(Double.NaN)
                 .append(" ").append(Double.POSITIVE_INFINITY)
@@ -114,7 +116,7 @@ public class StringBuilderTest {
         assertEquals("1.23456789E150 10.0 20.0 100.0 1000.0 0.1 0.01 1.0E20 2.0E20 1.0E-12"
                 + " -1.23456789E150 1.23456789E-150 1.79769313486231E308 3.0E-308"
                 + " 1200.0 0.023"
-                + " 0.0 1.0 NaN Infinity -Infinity", sb.toString());
+                + " 0.0 -0.0 1.0 NaN Infinity -Infinity", sb.toString());
     }
 
     @Test