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PHP should preserve the least significant bits when casting from double to long. Zend.m4 contains this: AC_DEFINE([ZEND_DVAL_TO_LVAL_CAST_OK], 1, [Define if double cast to long preserves least significant bits]) If ZEND_DVAL_TO_LVAL_CAST_OK is not defined, zend_operators.h had an inline implementation of zend_dval_to_lval() that would do a cast to an int64_t (when sizeof(long) == 4), then a cast to unsigned long and finally the cast to long. While this works well for doubles inside the range of values of the type used in the first cast (int64_t in the 32-bit version and unsigned long in the 64-bit version), if outside the range, it is undefined behavior that WILL give varying and not particularly useful results. This commit uses fmod() to first put the double in a range that can safely be cast to unsigned long and then casts this unsigned long to long. This last cast is implementation defined, but it's very likely that this gives the expected result (i.e. the internal 2's complement representation is unchanged) on all platforms that PHP supports. In any case, the previous implementationa already had this assumption. This alternative code path is indeed significantly slower than simply casting the double (almost an order of magnitude), but that should not matter because casting doubles with a very high absolute value is a rare event.
30 lines
547 B
PHP
30 lines
547 B
PHP
--TEST--
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zend_dval_to_lval preserves low bits (64 bit long)
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--SKIPIF--
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<?php
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if (PHP_INT_SIZE != 8)
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die("skip for machines with 64-bit longs");
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?>
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--FILE--
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<?php
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/* test doubles around -4e21 */
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$values = [
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-4000000000000001048576.,
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-4000000000000000524288.,
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-4000000000000000000000.,
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-3999999999999999475712.,
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-3999999999999998951424.,
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];
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foreach ($values as $v) {
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var_dump((int)$v);
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}
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?>
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--EXPECT--
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int(2943463994971652096)
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int(2943463994972176384)
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int(2943463994972700672)
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int(2943463994973224960)
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int(2943463994973749248)
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