Merge pull request #6 from xp-framework/refactor/raising_zero_to_power_of_negative_number

Make Big(Int|Float)::power() consistent with IEEE 754 rules

Author: thekid

ChangeLog.md

@@ -3,6 +3,12 @@ XP Math changelog
 
 ## ?.?.? / ????-??-??
 
+## 10.0.0 / ????-??-??
+
+* Merged PR #6: Make `Big(Int|Float)::power()` consistent with IEEE 754
+  rules, see issue #5.
+  (@thekid)
+
 ## 9.3.0 / 2024-03-24
 
 * Made compatible with XP 12 - @thekid

src/main/php/math/BigFloat.class.php

@@ -78,6 +78,10 @@ public function divide($other) {
    * @return math.BigNum
    */
   public function power($other) {
+    if (0 === bccomp($this->num, 0) && -1 === bccomp($other instanceof self ? $other->num : $other, 0)) {
+      throw new IllegalArgumentException('Negative power of zero');
+    }
+
     return new self(bcpow($this->num, $other instanceof self ? $other->num : $other));
   }
 

src/main/php/math/BigInt.class.php

@@ -169,11 +169,15 @@ public function divide0($other) {
   /**
    * ^
    *
-   * @see     http://en.wikipedia.org/wiki/Exponentiation
+   * @see    http://en.wikipedia.org/wiki/Exponentiation
    * @param  math.BigNum|int|float|string $other
    * @return math.BigNum
    */
   public function power($other) {
+    if (0 === bccomp($this->num, 0) && -1 === bccomp($other instanceof self ? $other->num : $other, 0)) {
+      throw new IllegalArgumentException('Negative power of zero');
+    }
+
     if ($other instanceof self) {
       return new self(bcpow($this->num, $other->num));
     } else if (is_int($other)) {

src/test/php/math/unittest/BigFloatTest.class.php

@@ -184,9 +184,9 @@ public function powerOfZeroZero() {
     Assert::equals(new BigFloat(1.0), (new BigFloat(0.0))->power(new BigFloat(0.0)));
   }
 
-  #[Test]
+  #[Test, Expect(IllegalArgumentException::class)]
   public function powerOfZeroNegative() {
-    Assert::equals(new BigFloat(0.0), (new BigFloat(0.0))->power(new BigFloat(-2)));
+    (new BigFloat(0.0))->power(new BigFloat(-2));
   }
 
   #[Test]

src/test/php/math/unittest/BigIntTest.class.php

@@ -239,9 +239,9 @@ public function powerOfZeroZero() {
     Assert::equals(new BigInt(1), (new BigInt(0))->power(new BigInt(0)));
   }
 
-  #[Test]
+  #[Test, Expect(IllegalArgumentException::class)]
   public function powerOfZeroNegative() {
-    Assert::equals(new BigInt(0), (new BigInt(0))->power(new BigInt(-2)));
+    (new BigInt(0))->power(new BigInt(-2));
   }
 
   #[Test]