Changes the CPU rounding mode only during a specific process.

Author: SakiTakamachi

ext/standard/math.c

@@ -27,6 +27,7 @@
 #include <float.h>
 #include <math.h>
 #include <stdlib.h>
+#include <fenv.h>
 
 #include "basic_functions.h"
 
@@ -46,32 +47,58 @@ static inline double php_intpow10(int power) {
 }
 /* }}} */
 
-#define PHP_ROUND_GET_EDGE_CASE(adjusted_value, value_abs, integral, exponent) do {\
-	if (fabs(adjusted_value) >= value_abs) {\
-		edge_case = fabs((integral + copysign(0.5, integral)) / exponent);\
-	} else {\
-		edge_case = fabs((integral + copysign(0.5, integral)) * exponent);\
-	}\
-} while(0);
-
-#define PHP_ROUND_GET_ZERO_EDGE_CASE(adjusted_value, value_abs, integral, exponent) do {\
-	if (fabs(adjusted_value) >= value_abs) {\
-		edge_case = fabs((integral) / exponent);\
-	} else {\
-		edge_case = fabs((integral) * exponent);\
-	}\
-} while(0);
-
 /* {{{ php_round_helper
        Actually performs the rounding of a value to integer in a certain mode */
-static inline double php_round_helper(double adjusted_value, double value, double exponent, int mode) {
-	double integral = adjusted_value >= 0.0 ? floor(adjusted_value) : ceil(adjusted_value);
+static inline double php_round_helper(double adjusted_value, double value, double exponent, int places, int mode) {
+	/**
+	 * When extracting the integer part, the result may be incorrect as a decimal
+	 * number due to floating point errors.
+	 * e.g.
+	 * 0.285 * 10000000000 => 2849999999.9999995
+	 * floor(0.285 * 10000000000) => 2849999999
+	 *
+	 * Therefore, change the CPU rounding mode to away from 0 only from
+	 * PHP_ROUND_GET_CURRENT_REG to PHP_ROUND_RESTORE_REG.
+	 * e.g.
+	 * 0.285 * 10000000000 => 2850000000.0
+	 * floor(0.285 * 10000000000) => 2850000000
+	 */
+	double integral;
+	int cpu_round_mode = fegetround();
+	if (value >= 0.0) {
+		fesetround(FE_UPWARD);
+		integral = floor(places > 0  ? value * exponent : value / exponent);
+	} else {
+		fesetround(FE_DOWNWARD);
+		integral = ceil(places > 0  ? value * exponent : value / exponent);
+	}
+	fesetround(cpu_round_mode);
+
 	double value_abs = fabs(value);
 	double edge_case;
 
 	switch (mode) {
 		case PHP_ROUND_HALF_UP:
-			PHP_ROUND_GET_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
+		case PHP_ROUND_HALF_DOWN:
+		case PHP_ROUND_HALF_EVEN:
+		case PHP_ROUND_HALF_ODD:
+			if (fabs(adjusted_value) >= value_abs) {
+				edge_case = fabs((integral + copysign(0.5, integral)) / exponent);
+			} else {
+				edge_case = fabs((integral + copysign(0.5, integral)) * exponent);
+			}
+			break;
+		default:
+			if (fabs(adjusted_value) >= value_abs) {
+				edge_case = fabs((integral) / exponent);
+			} else {
+				edge_case = fabs((integral) * exponent);
+			}
+			break;
+	}
+
+	switch (mode) {
+		case PHP_ROUND_HALF_UP:
 			if (value_abs >= edge_case) {
 				/* We must increase the magnitude of the integral part
 				 * (rounding up / towards infinity). copysign(1.0, integral)
@@ -87,23 +114,20 @@ static inline double php_round_helper(double adjusted_value, double value, doubl
 			return integral;
 
 		case PHP_ROUND_HALF_DOWN:
-			PHP_ROUND_GET_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
 			if (value_abs > edge_case) {
 				return integral + copysign(1.0, integral);
 			}
 
 			return integral;
 
 		case PHP_ROUND_CEILING:
-			PHP_ROUND_GET_ZERO_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
 			if (value > 0.0 && value_abs > edge_case) {
 				return integral + 1.0;
 			}
 
 			return integral;
 
 		case PHP_ROUND_FLOOR:
-			PHP_ROUND_GET_ZERO_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
 			if (value < 0.0 && value_abs > edge_case) {
 				return integral - 1.0;
 			}
@@ -114,15 +138,13 @@ static inline double php_round_helper(double adjusted_value, double value, doubl
 			return integral;
 
 		case PHP_ROUND_AWAY_FROM_ZERO:
-			PHP_ROUND_GET_ZERO_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
 			if (value_abs > edge_case) {
 				return integral + copysign(1.0, integral);
 			}
 
 			return integral;
 
 		case PHP_ROUND_HALF_EVEN:
-			PHP_ROUND_GET_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
 			if (value_abs > edge_case) {
 				return integral + copysign(1.0, integral);
 			} else if (UNEXPECTED(value_abs == edge_case)) {
@@ -139,7 +161,6 @@ static inline double php_round_helper(double adjusted_value, double value, doubl
 			return integral;
 
 		case PHP_ROUND_HALF_ODD:
-			PHP_ROUND_GET_EDGE_CASE(adjusted_value, value_abs, integral, exponent);
 			if (value_abs > edge_case) {
 				return integral + copysign(1.0, integral);
 			} else if (UNEXPECTED(value_abs == edge_case)) {
@@ -188,7 +209,7 @@ PHPAPI double _php_math_round(double value, int places, int mode) {
 	}
 
 	/* round the temp value */
-	tmp_value = php_round_helper(tmp_value, value, exponent, mode);
+    tmp_value = php_round_helper(tmp_value, value, exponent, places, mode);
 
 	/* see if it makes sense to use simple division to round the value */
 	if (abs(places) < 23) {
@@ -215,7 +236,6 @@ PHPAPI double _php_math_round(double value, int places, int mode) {
 			tmp_value = value;
 		}
 	}
-
 	return tmp_value;
 }
 /* }}} */