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6f56c00498
Signed multiply overflow is undefined behaviour. If you run the CI tests with UBSAN enabled on a 32-bit platform, this is quite easy to hit. On 64-bit it's more difficult to hit though, but not impossible. Closes GH-10942.
73 lines
3.1 KiB
C
73 lines
3.1 KiB
C
/*
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+----------------------------------------------------------------------+
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| Copyright (c) The PHP Group |
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+----------------------------------------------------------------------+
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| This source file is subject to version 3.01 of the PHP license, |
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| that is bundled with this package in the file LICENSE, and is |
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| available through the world-wide-web at the following url: |
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| https://www.php.net/license/3_01.txt |
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| If you did not receive a copy of the PHP license and are unable to |
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| obtain it through the world-wide-web, please send a note to |
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| license@php.net so we can mail you a copy immediately. |
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+----------------------------------------------------------------------+
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| Authors: Rasmus Lerdorf <rasmus@php.net> |
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| Zeev Suraski <zeev@php.net> |
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| Pedro Melo <melo@ip.pt> |
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| Sterling Hughes <sterling@php.net> |
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| |
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| Based on code from: Shawn Cokus <Cokus@math.washington.edu> |
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+----------------------------------------------------------------------+
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*/
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#ifndef PHP_RAND_H
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#define PHP_RAND_H
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#include "php_lcg.h"
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#include "php_mt_rand.h"
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/* System Rand functions */
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#ifndef RAND_MAX
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#define RAND_MAX PHP_MT_RAND_MAX
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#endif
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#define PHP_RAND_MAX PHP_MT_RAND_MAX
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/*
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* A bit of tricky math here. We want to avoid using a modulus because
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* that simply tosses the high-order bits and might skew the distribution
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* of random values over the range. Instead we map the range directly.
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*
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* We need to map the range from 0...M evenly to the range a...b
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* Let n = the random number and n' = the mapped random number
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*
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* Then we have: n' = a + n(b-a)/M
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*
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* We have a problem here in that only n==M will get mapped to b which
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# means the chances of getting b is much much less than getting any of
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# the other values in the range. We can fix this by increasing our range
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# artificially and using:
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#
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# n' = a + n(b-a+1)/M
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*
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# Now we only have a problem if n==M which would cause us to produce a
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# number of b+1 which would be bad. So we bump M up by one to make sure
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# this will never happen, and the final algorithm looks like this:
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#
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# n' = a + n(b-a+1)/(M+1)
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*
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* -RL
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*/
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#define RAND_RANGE_BADSCALING(__n, __min, __max, __tmax) \
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(__n) = (__min) + (zend_long) ((double) ( (double) (__max) - (__min) + 1.0) * ((__n) / ((__tmax) + 1.0)))
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#ifdef PHP_WIN32
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#define GENERATE_SEED() (((zend_long) ((zend_ulong) time(NULL) * (zend_ulong) GetCurrentProcessId())) ^ ((zend_long) (1000000.0 * php_combined_lcg())))
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#else
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#define GENERATE_SEED() (((zend_long) ((zend_ulong) time(NULL) * (zend_ulong) getpid())) ^ ((zend_long) (1000000.0 * php_combined_lcg())))
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#endif
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PHPAPI void php_srand(zend_long seed);
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PHPAPI zend_long php_rand(void);
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#endif /* PHP_RAND_H */
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