Zeev
At 18:01 13/09/2003, Ard Biesheuvel wrote:
Hello group,
Currently, the +, - en * operations in zend_operators in C do their calculcations on long arguments with doubles, and check if the result would fit in a long.
This failed for me on FreeBSD/alpha (in some of the math tests), because doubles are not accurate enough to represent LONG_MIN or LONG_MAX. This causes the comparison
'((double) LONG_MAX) + 1 > (double) LONG_MAX'
to result in 'false' because they have the same double representation.
Since a lot of tests use LONG_MAX in comparisons, this caused a lot of them to fail on this architecture.
One solution could be to use long doubles, but in my opinion it is better to check the sign bit directly.
A patch is attached.
-- Ard
Index: zend_operators.c =================================================================== RCS file: /repository/ZendEngine2/zend_operators.c,v retrieving revision 1.160 diff -u -r1.160 zend_operators.c --- zend_operators.c 17 Aug 2003 19:11:48 -0000 1.160 +++ zend_operators.c 13 Sep 2003 13:15:30 -0000 @@ -33,6 +33,8 @@ #include "ext/bcmath/number.h" #endif
+#define LONG_SIGN_MASK (1L << (8*SIZEOF_LONG-1)) + ZEND_API int zend_atoi(const char *str, int str_len) { int retval; @@ -664,13 +666,16 @@
if (op1->type == IS_LONG && op2->type == IS_LONG) {
- double dval = (double) op1->value.lval + (double) op2->value.lval;
+ long lval = op1->value.lval + op2->value.lval;
+
+ /* check for overflow by comparing sign bits */
+ if ( (op1->value.lval & LONG_SIGN_MASK) == (op2->value.lval & LONG_SIGN_MASK)
+ && (op1->value.lval & LONG_SIGN_MASK) != (lval & LONG_SIGN_MASK)) {
- if ((dval > (double) LONG_MAX) || (dval < (double) LONG_MIN)) {
- result->value.dval = dval;
+ result->value.dval = (double) op1->value.lval + (double) op2->value.lval;
result->type = IS_DOUBLE;
} else {
- result->value.lval = op1->value.lval + op2->value.lval;
+ result->value.lval = lval;
result->type = IS_LONG;
}
return SUCCESS;
@@ -701,13 +706,16 @@
zendi_convert_scalar_to_number(op2, op2_copy, result);
if (op1->type == IS_LONG && op2->type == IS_LONG) {
- double dval = (double) op1->value.lval - (double) op2->value.lval;
+ long lval = op1->value.lval - op2->value.lval;
+
+ /* check for overflow by comparing sign bits */
+ if ( (op1->value.lval & LONG_SIGN_MASK) != (op2->value.lval & LONG_SIGN_MASK)
+ && (op1->value.lval & LONG_SIGN_MASK) != (lval & LONG_SIGN_MASK)) {
- if ((dval < (double) LONG_MIN) || (dval > (double) LONG_MAX)) {
- result->value.dval = dval;
+ result->value.dval = (double) op1->value.lval - (double) op2->value.lval;
result->type = IS_DOUBLE;
} else {
- result->value.lval = op1->value.lval - op2->value.lval;
+ result->value.lval = lval;
result->type = IS_LONG;
}
return SUCCESS;
@@ -738,13 +746,14 @@
zendi_convert_scalar_to_number(op2, op2_copy, result);
if (op1->type == IS_LONG && op2->type == IS_LONG) {
- double dval = (double) op1->value.lval * (double) op2->value.lval;
-
- if ((dval > (double) LONG_MAX) || (dval < (double) LONG_MIN)) {
- result->value.dval = dval;
+ long lval = op1->value.lval * op2->value.lval;
+
+ /* check for overflow by applying the reverse calculation */
+ if (op1->value.lval != 0 && lval / op1->value.lval != op2->value.lval) {
+ result->value.dval = (double) op1->value.lval * (double) op2->value.lval;
result->type = IS_DOUBLE;
} else {
- result->value.lval = op1->value.lval * op2->value.lval;
+ result->value.lval = lval;
result->type = IS_LONG;
}
return SUCCESS;
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