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Date: Tue, 09 Mar 2004 16:50:50 +0100
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Subject: bug in zend_multiply.h
From: abies@php.net (Ard Biesheuvel)

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This code fails on 64-bit archs because it relies on the accuracy of a 
double to be sufficient to represent LONG_MAX. The patch adresses it by 
checking for overflow by reversing the calculation instead of casting to 
a double and back to long.


#include "build/php5-cvs/Zend/zend_multiply.h"

#define LONG_MIN (1L << (8*sizeof(long)-1))
#define LONG_MAX ~LONG_MIN

int main()
{
   long res = 0;
   double d = 0;
   int overflow;

   /* obviously (LONG_MAX-1) * 1 can be represented by a long */
   ZEND_SIGNED_MULTIPLY_LONG(LONG_MAX-1,1,res,d,overflow);

   printf("res: %ld/%.4f, %soverflow\n", result, d, overflow?"":"no ");
   return 0;
}



-- 
Ard

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--- Zend/zend_multiply.h	Sun Mar  7 13:59:35 2004
+++ Zend/zend_multiply.h.new	Wed Mar  3 09:14:04 2004
@@ -33,13 +33,13 @@
 #else
 
 #define ZEND_SIGNED_MULTIPLY_LONG(a, b, lval, dval, usedval) do {	\
-	double __tmpvar = (double) (a) * (double) (b);					\
+	long __tmpvar = (a) * (b);										\
 																	\
-	if (__tmpvar >= LONG_MAX || __tmpvar <= LONG_MIN) {				\
-		(dval) = __tmpvar;											\
+	if ((a) != 0 && __tmpvar / (a) != (b)) {						\
+		(dval) = (double)(a) * (double)(b);							\
 		(usedval) = 1;												\
 	} else {														\
-		(lval) = (a) * (b);											\
+		(lval) = __tmpvar;											\
 		(usedval) = 0;												\
 	}																\
 } while (0)

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