RFC: Raising zero to the power of negative number

NEWS

@@ -265,6 +265,7 @@ PHP                                                                        NEWS
     http_clear_last_response_headers() that allows retrieving the same content
     as the magic $http_response_header variable.
   . Add php_base64_encode_ex() API. (Remi)
+  . Implemented "Raising zero to the power of negative number" RFC (Jorg Sowa)
 
 - XML:
   . Added XML_OPTION_PARSE_HUGE parser option. (nielsdos)

UPGRADING

@@ -352,6 +352,7 @@ PHP 8.4 UPGRADE NOTES
 - Standard:
   . Calling stream_context_set_option() with 2 arguments is deprecated.
     Use stream_context_set_options() instead.
+  . Raising zero to the power of negative number is deprecated.
 
 ========================================
 5. Changed Functions
@@ -524,6 +525,7 @@ PHP 8.4 UPGRADE NOTES
   . Added the http_get_last_response_headers() and
     http_clear_last_response_headers() that allows retrieving the same content
     as the magic $http_response_header variable.
+  . Added function fpow() following rules of IEEE 754.
 
 - XSL:
   . Added XSLTProcessor::registerPhpFunctionNS().

Zend/tests/runtime_compile_time_binary_operands.phpt

@@ -8,6 +8,7 @@ if (getenv("SKIP_SLOW_TESTS")) die('skip slow test');
 ?>
 --FILE--
 <?php
+error_reporting(E_ALL ^ E_DEPRECATED);
 
 $binaryOperators = [
     "==",
@@ -122,7 +123,7 @@ function prepareBinaryLine($op1, $op2, $cmp, $operator) {
     try {
         $result = makeParam($cmp());
         $line .= "if (" . ($result === "(NAN)" ? "!is_nan($compare)" : "$compare !== $result") . ") { $error }";
-    } catch (Error $e) {
+    } catch (Throwable $e) {
         $msg = makeParam($e->getMessage());
         $line .= "try { $compare; $error } catch (Error \$e) { if (\$e->getMessage() !== $msg) { $error } }";
     }
@@ -138,7 +139,7 @@ function prepareUnaryLine($op, $cmp, $operator) {
     try {
         $result = makeParam($cmp());
         $line .= "if (" . ($result === "(NAN)" ? "!is_nan($compare)" : "$compare !== $result") . ") { $error }";
-    } catch (Error $e) {
+    } catch (Throwable $e) {
         $msg = makeParam($e->getMessage());
         $line .= "try { $compare; $error } catch (Error \$e) { if (\$e->getMessage() !== $msg) { $error } }";
     }

Zend/zend_compile.c

@@ -7714,7 +7714,7 @@ static zend_string *zend_begin_func_decl(znode *result, zend_op_array *op_array,
 		zend_string *separator = zend_empty_string;
 		zend_string *function = filename;
 		char *parens = "";
-		
+
 		if (CG(active_op_array) && CG(active_op_array)->function_name) {
 			if (CG(active_op_array)->fn_flags & ZEND_ACC_CLOSURE) {
 				/* If the parent function is a closure, don't redundantly
@@ -8980,6 +8980,10 @@ ZEND_API bool zend_binary_op_produces_error(uint32_t opcode, const zval *op1, co
 		/* Division by zero throws an error. */
 		return 1;
 	}
+	if ((opcode == ZEND_POW) && zval_get_long(op1) == 0 && zval_get_long(op2) < 0) {
+		/* 0 ** (<0) throws a division by zero error. */
+        return 1;
+	}
 	if ((opcode == ZEND_SL || opcode == ZEND_SR) && zval_get_long(op2) < 0) {
 		/* Shift by negative number throws an error. */
 		return 1;

Zend/zend_operators.c

@@ -1287,6 +1287,20 @@ ZEND_API zend_result ZEND_FASTCALL mul_function(zval *result, zval *op1, zval *o
 }
 /* }}} */
 
+static void ZEND_COLD zend_power_base_0_exponent_lt_0_error(void)
+{
+	zend_error(E_DEPRECATED, "Power of base 0 and negative exponent is deprecated");
+}
+
+static double safe_pow(double base, double exponent)
+{
+	if (UNEXPECTED(base == 0.0 && exponent < 0.0)) {
+		zend_power_base_0_exponent_lt_0_error();
+	}
+
+	return pow(base, exponent);
+}
+
 static zend_result ZEND_FASTCALL pow_function_base(zval *result, zval *op1, zval *op2) /* {{{ */
 {
 	uint8_t type_pair = TYPE_PAIR(Z_TYPE_P(op1), Z_TYPE_P(op2));
@@ -1311,32 +1325,32 @@ static zend_result ZEND_FASTCALL pow_function_base(zval *result, zval *op1, zval
 					--i;
 					ZEND_SIGNED_MULTIPLY_LONG(l1, l2, l1, dval, overflow);
 					if (overflow) {
-						ZVAL_DOUBLE(result, dval * pow(l2, i));
+						ZVAL_DOUBLE(result, dval * safe_pow(l2, i));
 						return SUCCESS;
 					}
 				} else {
 					i /= 2;
 					ZEND_SIGNED_MULTIPLY_LONG(l2, l2, l2, dval, overflow);
 					if (overflow) {
-						ZVAL_DOUBLE(result, (double)l1 * pow(dval, i));
+						ZVAL_DOUBLE(result, (double)l1 * safe_pow(dval, i));
 						return SUCCESS;
 					}
 				}
 			}
 			/* i == 0 */
 			ZVAL_LONG(result, l1);
 		} else {
-			ZVAL_DOUBLE(result, pow((double)Z_LVAL_P(op1), (double)Z_LVAL_P(op2)));
+			ZVAL_DOUBLE(result, safe_pow((double)Z_LVAL_P(op1), (double)Z_LVAL_P(op2)));
 		}
 		return SUCCESS;
 	} else if (EXPECTED(type_pair == TYPE_PAIR(IS_DOUBLE, IS_DOUBLE))) {
-		ZVAL_DOUBLE(result, pow(Z_DVAL_P(op1), Z_DVAL_P(op2)));
+		ZVAL_DOUBLE(result, safe_pow(Z_DVAL_P(op1), Z_DVAL_P(op2)));
 		return SUCCESS;
 	} else if (EXPECTED(type_pair == TYPE_PAIR(IS_LONG, IS_DOUBLE))) {
-		ZVAL_DOUBLE(result, pow((double)Z_LVAL_P(op1), Z_DVAL_P(op2)));
+		ZVAL_DOUBLE(result, safe_pow((double)Z_LVAL_P(op1), Z_DVAL_P(op2)));
 		return SUCCESS;
 	} else if (EXPECTED(type_pair == TYPE_PAIR(IS_DOUBLE, IS_LONG))) {
-		ZVAL_DOUBLE(result, pow(Z_DVAL_P(op1), (double)Z_LVAL_P(op2)));
+		ZVAL_DOUBLE(result, safe_pow(Z_DVAL_P(op1), (double)Z_LVAL_P(op2)));
 		return SUCCESS;
 	} else {
 		return FAILURE;

ext/standard/basic_functions.stub.php

@@ -3274,6 +3274,11 @@ function fmod(float $num1, float $num2): float {}
  */
 function fdiv(float $num1, float $num2): float {}
 
+/**
+ * @compile-time-eval
+ */
+function fpow(float $num1, float $num2): float {}
+
 /* microtime.c */
 
 #ifdef HAVE_GETTIMEOFDAY

ext/standard/math.c

@@ -1389,6 +1389,20 @@ PHP_FUNCTION(fdiv)
 }
 /* }}} */
 
+/* {{{ Perform floating-point exponentiation with IEEE-754 semantics. */
+PHP_FUNCTION(fpow)
+{
+    double base, exponent;
+
+    ZEND_PARSE_PARAMETERS_START(2, 2)
+        Z_PARAM_DOUBLE(base)
+        Z_PARAM_DOUBLE(exponent)
+    ZEND_PARSE_PARAMETERS_END();
+
+    RETURN_DOUBLE(pow(base, exponent));
+}
+/* }}} */
+
 /* {{{ Returns the integer quotient of the division of dividend by divisor */
 PHP_FUNCTION(intdiv)
 {

ext/standard/tests/math/bug45712.phpt

@@ -42,7 +42,7 @@ var_dump($inf==='abc');
 var_dump($inf===$inf);
 
 ?>
---EXPECT--
+--EXPECTF--
 float(NAN)
 bool(true)
 bool(false)
@@ -57,6 +57,8 @@ bool(false)
 bool(false)
 bool(false)
 bool(false)
+
+Deprecated: Power of base 0 and negative exponent is deprecated in %s on line %d
 float(INF)
 bool(true)
 bool(false)