Description:
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I'm using PHP 5.4.17 (cli) (built: Aug 25 2013 02:03:38), the default shipped by Apple now.

See the test script. When a string-representation of a decimal is large enough, converting it to a float causes "Fatal error: Balloc() allocation exceeds list boundary in php shell code on line 1" and terminates the script. This is similar to Ruby's bug, publicized at https://www.ruby-lang.org/en/news/2013/11/22/heap-overflow-in-floating-point-parsing-cve-2013-4164/.

Ruby fixed this by avoiding the Bigint freelist in Balloc; perhaps PHP should do something better than having a hard cutoff for k in Balloc.

Test script:
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echo floatval("1.".str_repeat("1", 300000));

Expected result:
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1.1111111111111, which is the output of echo floatval("1.".str_repeat("1", 300));

Actual result:
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Fatal error: Balloc() allocation exceeds list boundary in php shell code on line 1